Moving-average-model-in-r

Moving-average-model-in-r

Trading-system-c ++
I-stock-options-iso
Strategi-strategi hedging-pilihan


Pilihan-strategi-kupu-kupu Jak-czytac-wykresy-na-forex Trading-strategy-using-options Uk-binary-option-trading Online-trading-guide-for-pemula Pilihan nilai-nilai-pilihan-des-plus-values-stock

Pengantar ARIMA: model nonseasonal Persamaan peramalan ARIMA (p, d, q): Model ARIMA secara teori adalah kelas model paling umum untuk meramalkan deret waktu yang dapat dibuat dengan cara membedakan (jika perlu), mungkin Dalam hubungannya dengan transformasi nonlinier seperti logging atau deflating (jika perlu). Variabel acak yang merupakan deret waktu adalah stasioner jika sifat statistiknya konstan sepanjang waktu. Seri stasioner tidak memiliki tren, variasinya berkisar rata-rata memiliki amplitudo konstan, dan bergoyang secara konsisten. Yaitu pola waktu acak jangka pendeknya selalu terlihat sama dalam arti statistik. Kondisi terakhir ini berarti autokorelasinya (korelasi dengan penyimpangannya sendiri dari mean) tetap konstan dari waktu ke waktu, atau ekuivalen, bahwa spektrum kekuatannya tetap konstan seiring berjalannya waktu. Variabel acak dari bentuk ini dapat dilihat (seperti biasa) sebagai kombinasi sinyal dan noise, dan sinyal (jika ada) dapat menjadi pola reversi rata-rata yang cepat atau lambat, atau osilasi sinusoidal, atau alternasi cepat pada tanda , Dan itu juga bisa memiliki komponen musiman. Model ARIMA dapat dilihat sebagai filter 8220filter8221 yang mencoba memisahkan sinyal dari noise, dan sinyal tersebut kemudian diekstrapolasikan ke masa depan untuk mendapatkan perkiraan. Persamaan peramalan ARIMA untuk rangkaian waktu stasioner adalah persamaan linier (yaitu regresi-tipe) dimana prediktor terdiri dari kelambatan variabel dependen dan atau lag dari kesalahan perkiraan. Yaitu: Prediksi nilai Y adalah konstanta dan atau jumlah tertimbang dari satu atau lebih nilai Y dan satu angka tertimbang dari satu atau lebih nilai kesalahan terkini. Jika prediktor hanya terdiri dari nilai Y yang tertinggal, itu adalah model autoregresif murni (8220 self-regressed8221), yang hanyalah kasus khusus dari model regresi dan yang dapat dilengkapi dengan perangkat lunak regresi standar. Sebagai contoh, model autoregresif orde pertama (8220AR (1) 8221) untuk Y adalah model regresi sederhana dimana variabel independennya hanya Y yang tertinggal satu periode (LAG (Y, 1) dalam Statgrafik atau YLAG1 dalam RegresIt). Jika beberapa prediktor tertinggal dari kesalahan, model ARIMA TIDAK merupakan model regresi linier, karena tidak ada cara untuk menentukan error8221 8220last period8417s sebagai variabel independen: kesalahan harus dihitung berdasarkan periode-ke-periode Saat model dipasang pada data. Dari sudut pandang teknis, masalah dengan menggunakan kesalahan tertinggal sebagai prediktor adalah bahwa prediksi model8217 bukanlah fungsi linear dari koefisien. Meskipun mereka adalah fungsi linier dari data masa lalu. Jadi, koefisien pada model ARIMA yang mencakup kesalahan tertinggal harus diestimasi dengan metode optimasi nonlinier (8220 climb-climbing8221) daripada hanya dengan memecahkan sistem persamaan. Akronim ARIMA adalah singkatan Auto-Regressive Integrated Moving Average. Lags dari rangkaian stasioner dalam persamaan peramalan disebut istilah quotautoregressivequot, kelambatan kesalahan perkiraan disebut istilah kuotasi rata-rata quotmoving, dan deret waktu yang perlu dibedakan untuk dijadikan stasioner disebut versi seri integimental dari seri stasioner. Model random-walk dan random-trend, model autoregresif, dan model smoothing eksponensial adalah kasus khusus model ARIMA. Model ARIMA nonseasonal diklasifikasikan sebagai model quotARIMA (p, d, q) quot, di mana: p adalah jumlah istilah autoregresif, d adalah jumlah perbedaan nonseason yang diperlukan untuk stasioneritas, dan q adalah jumlah kesalahan perkiraan yang tertinggal dalam Persamaan prediksi Persamaan peramalan dibangun sebagai berikut. Pertama, izinkan y menunjukkan perbedaan D dari Y. yang berarti: Perhatikan bahwa perbedaan kedua Y (kasus d2) bukanlah selisih 2 periode yang lalu. Sebaliknya, ini adalah perbedaan pertama perbedaan dari perbedaan pertama. Yang merupakan analog diskrit dari derivatif kedua, yaitu percepatan lokal dari seri daripada tren lokalnya. Dalam hal y. Persamaan peramalan umum adalah: Di sini parameter rata-rata bergerak (9528217s) didefinisikan sehingga tanda-tanda mereka negatif dalam persamaan, mengikuti konvensi yang diperkenalkan oleh Box dan Jenkins. Beberapa penulis dan perangkat lunak (termasuk bahasa pemrograman R) mendefinisikannya sehingga mereka memiliki tanda plus. Bila nomor aktual dicolokkan ke dalam persamaan, tidak ada ambiguitas, tapi penting untuk mengetahui konvensi mana yang digunakan perangkat lunak Anda saat Anda membaca hasilnya. Seringkali parameter dilambangkan dengan AR (1), AR (2), 8230, dan MA (1), MA (2), 8230 dll. Untuk mengidentifikasi model ARIMA yang sesuai untuk Y. Anda memulai dengan menentukan urutan differencing (D) perlu membuat stasioner seri dan menghilangkan fitur musiman musiman, mungkin bersamaan dengan transformasi yang menstabilkan varians seperti penebangan atau pengapuran. Jika Anda berhenti pada titik ini dan meramalkan bahwa rangkaian yang dibedakan konstan, Anda hanya memiliki model berjalan acak atau acak acak. Namun, rangkaian stationarized masih memiliki kesalahan autokorelasi, menunjukkan bahwa beberapa jumlah istilah AR (p 8805 1) dan beberapa persyaratan MA (q 8805 1) juga diperlukan dalam persamaan peramalan. Proses penentuan nilai p, d, dan q yang terbaik untuk seri waktu tertentu akan dibahas di bagian catatan selanjutnya (yang tautannya ada di bagian atas halaman ini), namun pratinjau beberapa jenis Model ARIMA nonseasonal yang biasa ditemui diberikan di bawah ini. ARIMA (1,0,0) model autoregresif orde pertama: jika seri stasioner dan autokorelasi, mungkin dapat diprediksi sebagai kelipatan dari nilai sebelumnya, ditambah konstanta. Persamaan peramalan dalam kasus ini adalah 8230 yang Y regresi pada dirinya sendiri tertinggal oleh satu periode. Ini adalah model konstanta 8220ARIMA (1,0,0) constant8221. Jika mean Y adalah nol, maka istilah konstan tidak akan disertakan. Jika koefisien kemiringan 981 1 positif dan kurang dari 1 besarnya (harus kurang dari 1 jika Y adalah stasioner), model tersebut menggambarkan perilaku rata-rata pada nilai periode berikutnya yang diperkirakan akan menjadi 981 1 kali sebagai Jauh dari mean sebagai nilai periode ini. Jika 981 1 negatif, ia memprediksi perilaku rata-rata dengan bergantian tanda, yaitu juga memprediksi bahwa Y akan berada di bawah rata-rata periode berikutnya jika berada di atas rata-rata periode ini. Dalam model autoregresif orde kedua (ARIMA (2,0,0)), akan ada istilah Y t-2 di sebelah kanan juga, dan seterusnya. Bergantung pada tanda dan besaran koefisien, model ARIMA (2,0,0) bisa menggambarkan sistem yang pembalikan rata-rata terjadi dengan mode sinusoidal oscillating, seperti gerak massa pada pegas yang mengalami guncangan acak. . ARIMA (0,1,0) berjalan acak: Jika seri Y tidak stasioner, model yang paling sederhana untuk model ini adalah model jalan acak, yang dapat dianggap sebagai kasus pembatas model AR (1) dimana autoregresif Koefisien sama dengan 1, yaitu deret dengan reversi mean yang jauh lebih lambat. Persamaan prediksi untuk model ini dapat ditulis sebagai: di mana istilah konstan adalah perubahan periode-ke-periode rata-rata (yaitu drift jangka panjang) di Y. Model ini dapat dipasang sebagai model regresi yang tidak mencegat dimana Perbedaan pertama Y adalah variabel dependen. Karena hanya mencakup perbedaan nonseasonal dan istilah konstan, model ini diklasifikasikan sebagai model quotARIMA (0,1,0) dengan konstan. Model acak-berjalan-tanpa-undian akan menjadi ARIMA (0,1, 0) model tanpa ARIMA konstan (1,1,0) membedakan model autoregresif orde pertama: Jika kesalahan model jalan acak autokorelasi, mungkin masalahnya dapat diperbaiki dengan menambahkan satu lag variabel dependen ke persamaan prediksi- -yaitu Dengan mengundurkan diri dari perbedaan pertama Y pada dirinya sendiri yang tertinggal satu periode. Ini akan menghasilkan persamaan prediksi berikut: yang dapat diatur ulang ke Ini adalah model autoregresif orde pertama dengan satu urutan perbedaan nonseasonal dan istilah konstan - yaitu. Sebuah model ARIMA (1,1,0). ARIMA (0,1,1) tanpa perataan eksponensial sederhana: Strategi lain untuk memperbaiki kesalahan autokorelasi dalam model jalan acak disarankan oleh model pemulusan eksponensial sederhana. Ingatlah bahwa untuk beberapa rangkaian waktu nonstasioner (misalnya yang menunjukkan fluktuasi yang bising di sekitar rata-rata yang bervariasi secara perlahan), model jalan acak tidak berjalan sebaik rata-rata pergerakan nilai masa lalu. Dengan kata lain, daripada mengambil pengamatan terbaru sebagai perkiraan pengamatan berikutnya, lebih baik menggunakan rata-rata beberapa pengamatan terakhir untuk menyaring kebisingan dan memperkirakan secara lebih akurat mean lokal. Model pemulusan eksponensial sederhana menggunakan rata-rata pergerakan rata-rata tertimbang eksponensial untuk mencapai efek ini. Persamaan prediksi untuk model pemulusan eksponensial sederhana dapat ditulis dalam sejumlah bentuk ekuivalen matematis. Salah satunya adalah bentuk koreksi yang disebut 8220error correction8221, dimana ramalan sebelumnya disesuaikan dengan kesalahan yang dibuatnya: Karena e t-1 Y t-1 - 374 t-1 menurut definisinya, ini dapat ditulis ulang sebagai : Yang merupakan persamaan peramalan ARIMA (0,1,1) - tanpa perkiraan konstan dengan 952 1 1 - 945. Ini berarti bahwa Anda dapat menyesuaikan smoothing eksponensial sederhana dengan menentukannya sebagai model ARIMA (0,1,1) tanpa Konstan, dan perkiraan koefisien MA (1) sesuai dengan 1-minus-alpha dalam formula SES. Ingatlah bahwa dalam model SES, usia rata-rata data dalam prakiraan 1 periode adalah 1 945. yang berarti bahwa mereka cenderung tertinggal dari tren atau titik balik sekitar 1 945 periode. Dengan demikian, rata-rata usia data dalam prakiraan 1-periode-depan model ARIMA (0,1,1) - tanpa model konstan adalah 1 (1 - 952 1). Jadi, misalnya, jika 952 1 0,8, usia rata-rata adalah 5. Karena 952 1 mendekati 1, model ARIMA (0,1,1) -tanpa-konstan menjadi rata-rata bergerak jangka-panjang, dan sebagai 952 1 Pendekatan 0 menjadi model random-walk-without-drift. Apa cara terbaik untuk memperbaiki autokorelasi: menambahkan istilah AR atau menambahkan istilah MA Dalam dua model sebelumnya yang dibahas di atas, masalah kesalahan autokorelasi dalam model jalan acak diperbaiki dengan dua cara yang berbeda: dengan menambahkan nilai lag dari seri yang berbeda Ke persamaan atau menambahkan nilai tertinggal dari kesalahan perkiraan. Pendekatan mana yang terbaik Aturan praktis untuk situasi ini, yang akan dibahas lebih rinci nanti, adalah bahwa autokorelasi positif biasanya paling baik ditangani dengan menambahkan istilah AR pada model dan autokorelasi negatif biasanya paling baik ditangani dengan menambahkan MA istilah. Dalam deret waktu bisnis dan ekonomi, autokorelasi negatif sering muncul sebagai artefak perbedaan. (Secara umum, differencing mengurangi autokorelasi positif dan bahkan dapat menyebabkan perubahan dari autokorelasi positif ke negatif.) Jadi, model ARIMA (0,1,1), di mana perbedaannya disertai dengan istilah MA, lebih sering digunakan daripada Model ARIMA (1,1,0). ARIMA (0,1,1) dengan perataan eksponensial sederhana konstan dengan pertumbuhan: Dengan menerapkan model SES sebagai model ARIMA, Anda benar-benar mendapatkan fleksibilitas. Pertama-tama, perkiraan koefisien MA (1) dibiarkan negatif. Ini sesuai dengan faktor pemulusan yang lebih besar dari 1 dalam model SES, yang biasanya tidak diizinkan oleh prosedur pemasangan model SES. Kedua, Anda memiliki pilihan untuk menyertakan istilah konstan dalam model ARIMA jika Anda mau, untuk memperkirakan tren nol-rata-rata. Model ARIMA (0,1,1) dengan konstanta memiliki persamaan prediksi: Prakiraan satu periode dari model ini secara kualitatif serupa dengan model SES, kecuali bahwa lintasan perkiraan jangka panjang biasanya adalah Garis miring (kemiringannya sama dengan mu) dan bukan garis horizontal. ARIMA (0,2,1) atau (0,2,2) tanpa pemulusan eksponensial linier konstan: Model pemulusan eksponensial linier adalah model ARIMA yang menggunakan dua perbedaan nonseasonal dalam hubungannya dengan persyaratan MA. Perbedaan kedua dari seri Y bukan hanya perbedaan antara Y dan dirinya tertinggal dua periode, namun ini adalah perbedaan pertama dari perbedaan pertama - i. Perubahan perubahan Y pada periode t. Jadi, perbedaan kedua Y pada periode t sama dengan (Y t - Y t-1) - (Y t-1 - Y t-2) Y t - 2Y t-1 Y t-2. Perbedaan kedua dari fungsi diskrit sama dengan turunan kedua dari fungsi kontinu: ia mengukur kuotasi kuadrat atau quotcurvaturequot dalam fungsi pada suatu titik waktu tertentu. Model ARIMA (0,2,2) tanpa konstan memprediksi bahwa perbedaan kedua dari rangkaian sama dengan fungsi linier dari dua kesalahan perkiraan terakhir: yang dapat disusun ulang sebagai: di mana 952 1 dan 952 2 adalah MA (1) dan MA (2) koefisien. Ini adalah model pemulusan eksponensial linear umum. Dasarnya sama dengan model Holt8217s, dan model Brown8217s adalah kasus khusus. Ini menggunakan rata-rata pergerakan tertimbang eksponensial untuk memperkirakan tingkat lokal dan tren lokal dalam rangkaian. Perkiraan jangka panjang dari model ini menyatu dengan garis lurus yang kemiringannya bergantung pada tren rata-rata yang diamati menjelang akhir rangkaian. ARIMA (1,1,2) tanpa perataan eksponensial eksponensial yang terfragmentasi. Model ini diilustrasikan dalam slide yang menyertainya pada model ARIMA. Ini mengekstrapolasikan tren lokal di akhir seri namun meratakannya pada cakrawala perkiraan yang lebih panjang untuk memperkenalkan catatan konservatisme, sebuah praktik yang memiliki dukungan empiris. Lihat artikel di quotWhy the Damped Trend karyaquot oleh Gardner dan McKenzie dan artikel quotGolden Rulequot oleh Armstrong dkk. Untuk rinciannya Umumnya dianjurkan untuk berpegang pada model di mana setidaknya satu dari p dan q tidak lebih besar dari 1, yaitu jangan mencoba menyesuaikan model seperti ARIMA (2,1,2), karena hal ini cenderung menyebabkan overfitting. Dan isu-isu kuotom-faktorquot yang dibahas secara lebih rinci dalam catatan tentang struktur matematis model ARIMA. Implementasi Spreadsheet: Model ARIMA seperti yang dijelaskan di atas mudah diterapkan pada spreadsheet. Persamaan prediksi hanyalah persamaan linier yang mengacu pada nilai-nilai masa lalu dari rangkaian waktu asli dan nilai kesalahan masa lalu. Dengan demikian, Anda dapat membuat spreadsheet peramalan ARIMA dengan menyimpan data di kolom A, rumus peramalan pada kolom B, dan kesalahan (data minus prakiraan) di kolom C. Rumus peramalan pada sel biasa di kolom B hanya akan menjadi Sebuah ekspresi linier yang mengacu pada nilai-nilai pada baris-kolom sebelumnya dari kolom A dan C, dikalikan dengan koefisien AR atau MA yang sesuai yang disimpan di sel-sel di tempat lain pada spreadsheet.GASES, LIQUIDS dan aplikasi SOLIDS dari model partikel untuk tiga keadaan model partikel materi, Menjelaskan, menjelaskan sifat-sifat gas, cairan dan padatan Doc Browns Chemistry KS4 sains Catatan Revisi GCSEIGCSE Perbandingan sifatnya dari GASES, LIQUIDS and SOLIDS States of Matter catatan revisi gasliquidsolid Bagian 1 Model partikel kinetik dan menjelaskan dan menjelaskan sifat-sifat gas , Cairan dan padatan, perubahan dan solusi negara (bagian 1a sampai 3d) Anda harus tahu bahwa ketiga keadaan materi itu padat, cair dan gas. Peleburan dan pembekuan berlangsung pada titik leleh, mendidih dan kondensasi berlangsung pada titik didih. Ketiga keadaan materi dapat diwakili oleh model sederhana di mana partikel diwakili oleh bola padat kecil. Teori partikel dapat membantu menjelaskan pencairan, perebusan, pembekuan dan pengembunan. Jumlah energi yang diperlukan untuk mengubah keadaan dari padatan menjadi cair dan dari cair ke gas bergantung pada kekuatan kekuatan antara partikel substansi dan sifat partikel yang terlibat tergantung pada jenis ikatan dan struktur zat. Semakin kuat kekuatan antar partikel semakin tinggi titik leleh dan titik didih zat. Untuk rinciannya lihat struktur dan catatan ikatan. Keadaan fisik yang diadopsi material bergantung pada struktur, suhu dan tekanannya. Simbol negara yang digunakan dalam persamaan: (g) larutan cairan padat aqous (aq) berair (aq) larutan padat berarti sesuatu yang dilarutkan dalam air Sebagian besar diagram partikel pada halaman ini adalah representasi 2D dari struktur dan keadaannya CONTOH TIGA FISIK STATES OF MATTER GASES mis Campuran udara di sekitar kita (termasuk oksigen yang dibutuhkan untuk pembakaran) dan uap bertekanan tinggi pada boiler dan silinder lokomotif uap. Semua gas di udara tidak terlihat, tidak berwarna dan transparan. Perhatikan bahwa uap yang Anda lihat di luar ketel atau lokomotif uap sebenarnya adalah tetesan cairan air yang halus, terbentuk dari uap gas buang yang dikeluarkan saat memenuhi udara dingin perubahan gas ke cairan (efek yang sama pada kabut dan kabut) . LIQUIDS mis. Air adalah contoh yang paling umum, tapi begitu juga susu, mentega panas, bensin, minyak, merkuri atau alkohol dalam termometer. SOLIDS mis. Batu, semua logam pada suhu kamar (kecuali merkuri), karet sepatu boot dan sebagian besar benda fisik di sekitar Anda. Sebenarnya sebagian besar benda tidak berguna kecuali jika memiliki struktur padat. Pada halaman ini sifat fisik dasar gas, cairan dan padatan dijelaskan dalam bentuk struktur, gerakan partikel (teori partikel kinetik), efek perubahan suhu dan tekanan, dan model partikel. Digunakan untuk menjelaskan sifat dan karakteristik ini. Mudah-mudahan, teori dan fakta akan sesuai untuk memberi para siswa pemahaman yang jelas tentang dunia material di sekitar mereka dalam hal gas, cairan dan padatan yang disebut sebagai tiga keadaan fisik materi. Perubahan keadaan yang dikenal sebagai pencairan, peleburan, pendidihan, penguapan, pengembunan, pencairan, pembekuan, pemadatan, kristalisasi dijelaskan dan dijelaskan dengan gambar model partikel untuk membantu pemahaman. Ada juga penyebutan cairan yang mudah larut dan tidak bercampur dan menjelaskan persyaratan volatile dan volatilitas saat diterapkan pada cairan. Catatan revisi tentang keadaan materi ini seharusnya berguna untuk kursus sains kimia AQA, Edexcel dan OCR GCSE (91) yang baru. Subindex untuk bagian Bagian I (halaman ini): 1.1. The Three States of Matter, model teori partikel gasliquidsolid Tiga keadaan materi padat, cair dan gas. Baik pencairan dan pembekuan bisa terjadi pada titik leleh, sedangkan mendidih dan kondensasi berlangsung pada titik didih. Penguapan bisa terjadi pada suhu apapun dari permukaan cair. Anda bisa mewakili tiga keadaan materi dengan model partikel sederhana. Dalam modeldiagrams ini, partikel diwakili oleh bola padat kecil (struktur elektron diabaikan). Teori partikel kinetik dapat membantu menjelaskan perubahan keadaan seperti pencairan, pendinginan, pembekuan dan pengembunan. Jumlah energi yang dibutuhkan untuk mengubah keadaan dari padatan menjadi cair atau dari cair ke gas bergantung pada kekuatan kekuatan antara partikel substansi. Kekuatan ini mungkin merupakan kekuatan intermolekuler yang relatif lemah (ikatan antarmolekul) atau ikatan kimia kuat (ionik, kovalen atau logam). Sifat partikel yang terlibat tergantung pada jenis ikatan kimia dan struktur zat. Semakin kuat kekuatan tarik antara partikel semakin tinggi titik lebur dan titik didih zatnya APA ITU TIGA NEGARA MATERI Sebagian besar bahan dapat digambarkan sebagai gas, cair atau padat. MENGAPA MEREKA SEPERTI APA YANG MEREKA Saja mengetahui cukup, kita membutuhkan teori gas yang komprehensif, yang dapat menjelaskan perilaku mereka dan membuat prediksi tentang apa yang terjadi mis. Jika kita mengubah suhu atau tekanan. BAGAIMANA KITA MENJELASKAN BAGAIMANA MEREKA MEMILIKI Kita memerlukan model teoritis mis. Teori partikel yang didukung oleh bukti eksperimental. MODEL PARTIKEL YANG BISA MEMBANTU KAMI MEMAHAMI SIFAT DAN KARAKTERISTIK MEREKA MENGAPA SAYA PENTING UNTUK MENGETAHUI SIFAT-SIFATNYA GAS, LIQUIDS DAN SOLIDS Penting dalam industri kimia untuk mengetahui tentang perilaku gas, cairan dan padatan dalam proses kimia mis. Apa yang terjadi pada keadaan yang berbeda dengan perubahan suhu dan tekanan. Apa itu TEORI PARTIKEL KINETIKA, cairan dan padatan Teori partikel kinetik keadaan materi didasarkan pada gagasan semua bahan yang ada sebagai partikel sangat kecil yang mungkin merupakan atom atau molekul individu dan interaksinya satu sama lain. Oleh tabrakan dalam gas atau cairan atau oleh getaran dan ikatan kimia dalam padatan. DAPATKAN KAMI MEMBUAT PREDIKSI BERDASARKAN SIFAT-SIFAT KARAKTERISTIK Halaman ini memperkenalkan deskripsi fisik umum zat-zat di tingkat klasifikasi fisik (nonkritis) yang paling sederhana yaitu gas, cairan atau zat padat. NAMUN, halaman web ini juga memperkenalkan model partikel di mana lingkaran kecil mewakili sebuah atom atau molekul yaitu partikel tertentu atau satuan zat yang paling sederhana. Bagian ini cukup abstrak karena Anda berbicara tentang partikel yang tidak dapat Anda lihat secara terpisah, hanya material massal dan karakter fisik dan propertinya. Apakah ada LIMITASI pada model partikel Partikel diperlakukan sebagai bola inelastis sederhana dan hanya berperilaku seperti bola snooker menit yang terbang di sekitar, tidak sepenuhnya benar, tapi terbang melintas secara acak tanpa henti Meskipun partikel diasumsikan sebagai bola keras dan inelastis. , Pada kenyataannya mereka adalah segala bentuk dan putaran dan tekuk pada tumbukan dengan partikel lain dan ketika mereka bereaksi, mereka terbagi menjadi fragmen saat ikatan pecah. Model sederhana tidak mengasumsikan kekuatan di antara partikel-partikel itu, tidak benar, model ini memperhitungkan sedikit kekuatan di antara partikel-partikel, bahkan pada gas-gas yang Anda dapatkan dengan kekuatan antarmolekul sangat lemah. Model partikel tidak memperhitungkan ukuran sebenarnya partikel mis. Ionsmolekul dapat berukuran berbeda secara luas mis. Bandingkan molekul etena dengan molekul poli (etena) Ruang di antara partikel APA ITU NEGARA YANG BERKELANJUTAN APA YANG DAPAT DILARANG DARI GAS BAGAIMANA BERBAGAI PARTIKEL BERBEDA Bagaimana teori teori partikel kinetik menjelaskan sifat gas A gas Tidak memiliki bentuk atau volume tetap, tapi selalu menyebar untuk mengisi wadah - molekul gas akan berdifusi ke tempat yang tersedia. Hampir tidak ada kekuatan tarik-menarik antara partikel sehingga mereka benar-benar bebas satu sama lain. Partikel secara luas ditempatkan dan tersebar pada bergerak cepat secara acak ke seluruh wadah sehingga tidak ada ketertiban dalam sistem. Partikel bergerak secara linier dan cepat ke segala arah. Dan sering bertabrakan satu sama lain dan sisi wadah. Tumbukan partikel gas dengan permukaan wadah menyebabkan tekanan gas. Pada memantul dari permukaan mereka mengerahkan kekuatan dalam melakukannya. Dengan kenaikan suhu. Partikel bergerak lebih cepat saat mereka mendapatkan energi kinetik. Tingkat tumbukan antara partikel itu sendiri dan permukaan wadah meningkat dan ini meningkatkan tekanan gas misalnya di lokomotif uap atau volume wadah jika bisa meluas misalnya seperti balon. Gas memiliki kerapatan (cahaya) sangat rendah karena partikelnya begitu berjarak dalam wadah (density mass volume). Density order: gas cair gtgtgt gt gtgtgt Gas mengalir dengan bebas karena tidak ada kekuatan daya tarik yang efektif antara molekul partikel gas. Kemudahan urutan aliran. Cairan gtgtgt cair (tidak ada aliran nyata dalam padatan kecuali jika Anda mengaduknya) Karena gas dan cairan ini digambarkan sebagai cairan. Gas tidak memiliki permukaan. Dan tidak ada bentuk atau volume tetap. Dan karena kurangnya daya tarik partikel, mereka selalu menyebar dan mengisi wadah apapun (jadi volume volume gas kontainer). Gas mudah dikompres karena ruang kosong di antara partikel. Kemudahan kompresi order. Gas gas Bila gas dikurung dalam wadah, partikel akan menyebabkan dan menggunakan tekanan gas yang diukur di atmosfir (atm) atau Pascal (1,0 Pa 1,0 Nm 2), gas tidak mengandung zat terlarut. Tekanan adalah forcearea yaitu efek dari semua tumbukan pada permukaan wadah. Tekanan gas disebabkan oleh kekuatan yang diciptakan oleh jutaan dampak partikel gas kecil individu di sisi wadah. Misalnya, jika jumlah partikel gas dalam wadah berlipat ganda, tekanan gas dua kali lipat karena dua kali lipat jumlah molekul melipatgandakan jumlah dampak pada sisi wadah sehingga kekuatan benturan total per satuan luas juga berlipat ganda. Dua kali lipat dari dampak partikel menggandakan tekanan digambarkan dalam dua diagram di bawah ini. Jika volume wadah tertutup rapat dijaga konstan dan gas di dalamnya dipanaskan sampai suhu yang lebih tinggi, tekanan gas akan meningkat. Alasan untuk ini adalah bahwa saat partikel dipanaskan, mereka mendapatkan energi kinetik dan bergerak rata-rata lebih cepat. Karena itu mereka akan bertabrakan dengan sisi kontainer dengan kekuatan benturan yang lebih besar. Sehingga meningkatkan tekanan. Ada juga frekuensi tabrakan yang lebih besar dengan sisi wadah NAMUN ini merupakan faktor minor dibandingkan dengan efek peningkatan energi kinetik dan kenaikan rata-rata kekuatan benturan. Oleh karena itu jumlah gas yang tetap dalam wadah tertutup dengan volume konstan, semakin tinggi suhu semakin besar tekanan dan semakin rendah suhu, semakin rendah tekanannya. Untuk perhitungan gas pressuretemperature lihat Bagian 2 Hukum CharlessGayLussacs Jika volume wadah dapat berubah, gas mudah berkembang pada pemanasan karena kurangnya daya tarik partikel, dan siap berkontraksi pada pendinginan. Pada pemanasan, partikel gas mendapatkan energi kinetik. Bergerak lebih cepat dan tekan sisi wadah lebih sering. Dan secara signifikan, mereka memukul dengan kekuatan yang lebih besar. Bergantung pada situasi kontainer, salah satu atau kedua tekanan atau volume akan meningkat (terbalik pada pendinginan). Catatan: Ini adalah volume gas yang mengembang TIDAK molekulnya, mereka tetap berukuran sama Jika tidak ada batasan volume, ekspansi pada pemanasan jauh lebih besar untuk gas daripada cairan dan padatan karena tidak ada daya tarik yang signifikan antara partikel gas. Energi kinetik yang meningkat rata-rata akan membuat tekanan gas meningkat dan gas akan mencoba untuk memperluas volume jika diizinkan untuk mis. Balon di ruangan yang hangat secara signifikan lebih besar dari balon yang sama di ruangan yang dingin Untuk perhitungan volumetemperatur gas lihat Bagian 2 Hukum CharlessGayLussacs DIFUSI DALAM Gas: Gerakan cepat dan acak alami partikel ke segala arah berarti bahwa gas mudah menyebar atau menyebar. Pergerakan bersih gas tertentu akan berada di arah dari konsentrasi rendah ke konsentrasi yang lebih tinggi, turunkan gradien difusi socalled. Ffusi berlanjut sampai konsentrasi seragam di seluruh wadah gas, namun SEMUA partikel terus bergerak dengan energi kinetik yang pernah ada. Difusi lebih cepat terjadi pada gas daripada cairan dimana ada lebih banyak ruang untuk dipindahkan (percobaan diilustrasikan di bawah ini) dan difusi adalah Diabaikan dalam padatan karena pengepakan partikel yang dekat. Difusi bertanggung jawab atas penyebaran bau bahkan tanpa gangguan udara mis. Gunakan parfum, buka stoples kopi atau bau bensin di sekitar garasi. Laju difusi meningkat dengan kenaikan suhu saat partikel mendapatkan energi kinetik dan bergerak lebih cepat. Bukti lain untuk pergerakan partikel acak termasuk difusi. Ketika partikel asap dilihat di bawah mikroskop, mereka tampak menari saat diterangi sinar lampu pada suhu 90 o ke arah penayangan. Hal ini karena partikel asap muncul dengan memantulkan cahaya dan tarian karena jutaan hits acak dari molekul udara bergerak cepat. Ini disebut gerak Brown (lihat di bawah cairan). Pada saat tertentu, hitnya tidak akan genap, jadi partikel asapnya bisa menjadi pukulan yang lebih besar secara acak. Percobaan difusi dua molekul gas diilustrasikan di atas dan dijelaskan di bawah Sebuah tabung kaca panjang (diameter 24 cm) diisi di salah satu ujungnya dengan steker kapas yang direndam dalam conc. Asam klorida disegel dengan karet bung (untuk kesehatan dan keselamatan) dan tabung tetap terjaga diam, dijepit dalam posisi horizontal. Serangkaian conc yang serupa. Larutan amonia ditempatkan di ujung yang lain. Soket wol kapas yang dibasahi akan mengeluarkan asap HCl dan NH3 masing-masing, dan jika tabung dibiarkan tidak terganggu dan horizontal, meskipun tidak ada gerakan tabung, mis. Tidak bergetar untuk mencampur dan tidak adanya konveksi, awan putih terbentuk sekitar 1 3 rd sepanjang conc. Ujung tabung asam klorida. Penjelasan: Apa yang terjadi adalah gas tak berwarna, amonia dan hidrogen klorida, berdifusi ke tabung dan bereaksi membentuk kristal putih halus dari garam amonium klorida. Ammonia hidrogen klorida gt amonium klorida NH 3 (g) HCl (g) gt NH 4 Cl (s) Perhatikan aturannya: Semakin kecil massa molekulnya, semakin besar kecepatan rata-rata molekul (tetapi semua gas memiliki energi kinetik rata-rata yang sama Pada suhu yang sama). Oleh karena itu semakin kecil massa molekulnya, semakin cepat gas berdifusi. misalnya M r (NH 3) 14 1x3 17. Bergerak lebih cepat dari M r (HCl) 1 35,5 36,5 DAN itulah mengapa mereka bertemu di dekat ujung HCl dari tabung Jadi eksperimen tidak hanya merupakan bukti pergerakan molekul. Ini juga merupakan bukti bahwa molekul molekul yang berbeda bergerak dengan kecepatan berbeda. Untuk perawatan matematis lihat Grahams of the Difusion Sebuah gas berwarna, lebih berat dari pada udara (kepadatan lebih besar), dimasukkan ke dalam tabung gas bawah dan tabung gas kedua dari udara tanpa warna yang lebih rendah ditempatkan di atasnya dipisahkan dengan penutup kaca. Percobaan difusi harus tertutup pada suhu konstan untuk meminimalkan gangguan konveksi. Jika penutup kaca dilepaskan maka (i) gas udara tak berwarna berdifusi ke dalam gas coklat berwarna dan (ii) bromin berdifusi naik ke udara. Gerakan partikel acak yang mengarah ke pencampuran tidak dapat terjadi karena konveksi karena gas yang lebih padat mulai dari bawah. Tidak ada guncangan atau sarana pencampuran lainnya yang diperlukan. Gerakan acak kedua partikel cukup untuk memastikan bahwa kedua gas akhirnya menjadi benar-benar dicampur oleh difusi (menyebar satu sama lain). Ini adalah bukti yang jelas untuk difusi karena pergerakan kontinu acak dari semua partikel gas dan, pada awalnya, pergerakan bersih satu jenis partikel dari yang lebih tinggi ke konsentrasi yang lebih rendah (turunkan gradien difusi). Bila dicampur penuh, tidak ada perubahan distribusi warna lebih lanjut yang diamati. TAPI gerakan partikel acak terus berlanjut. Lihat juga bukti lain di bagian cairan setelah model partikel untuk diagram difusi di bawah ini. Sebuah model partikel difusi dalam gas. Bayangkan gradien difusi dari kiri ke kanan untuk partikel hijau ditambahkan ke partikel biru di sebelah kiri. Jadi, untuk partikel hijau, migrasi bersih dari kiri ke kanan dan akan berlanjut, dalam wadah tertutup, sampai semua partikel merata dalam wadah gas (seperti yang digambarkan). Difusi lebih cepat dalam gas dibandingkan dengan larutan cair karena ada lebih banyak ruang di antara partikel untuk partikel lain bergerak secara acak. Bila padat dipanaskan partikelnya bergetar lebih kuat saat mereka mendapatkan energi kinetik dan kekuatan tarik partikel melemah. Akhirnya, pada titik lebur. Kekuatan yang menarik terlalu lemah untuk menahan partikel dalam struktur secara teratur dan dengan demikian padatannya meleleh. Perhatikan bahwa kekuatan antarmolekul masih ada untuk menahan cairan curah bersama tapi efeknya tidak cukup kuat untuk membentuk kisi kristal yang dipesan dengan solid. Partikel menjadi bebas untuk bergerak dan kehilangan pengaturan tertata. Energi dibutuhkan untuk mengatasi daya tarik dan memberi partikel energi kinetik getaran yang meningkat. Jadi panas diambil dari sekitarnya dan mencair adalah proses endotermik (916H ve). Perubahan energi untuk perubahan keadaan fisik ini untuk berbagai zat ditangani di bagian Catatan Energetik. Dijelaskan menggunakan teori partikel kinetik cairan dan padatan Pada pendinginan, partikel cair kehilangan energi kinetik sehingga dapat menjadi lebih kuat tertarik satu sama lain. Bila suhunya cukup rendah, energi kinetik partikel tidak mencukupi untuk mencegah kekuatan menarik partikel yang menyebabkan padatan terbentuk. Akhirnya pada titik beku kekuatan daya tarik cukup untuk menghilangkan kebebasan bergerak yang tersisa (dalam hal satu tempat ke tempat lain) dan partikel berkumpul untuk membentuk susunan padat yang dipesan (walaupun partikelnya masih memiliki energi kinetik getaran. Harus dilepas ke sekitarnya, sangat aneh, pembekuan adalah proses eksotermik (916H) perubahan energi komparatif perubahan keadaan gas ltgt cair ltgt solid 2f (i) Kurva pendinginan Apa yang terjadi pada suhu suatu zat Jika didinginkan dari keadaan gas ke keadaan padat Perhatikan suhu tetap konstan selama perubahan keadaan kondensasi pada suhu Tc dan freezingsolidifying pada suhu Tf Hal ini karena semua energi panas dilepaskan pada pendinginan pada suhu ini (pemanasan laten Atau enthalpies of state change), memungkinkan penguatan kekuatan antarpartikel (ikatan antarmolekul) tanpa suhu turun. Kehilangan panas adalah kompensasi D oleh eksotermik meningkatkan daya tarik antarmolekul. Di antara bagian perubahan keadaan horizontal pada grafik, Anda dapat melihat penghilangan energi mengurangi energi kinetik partikel, menurunkan suhu zat. Lihat bagian 2. untuk penjelasan rinci tentang perubahan negara. Kurva pendinginan merangkum perubahan: Untuk setiap perubahan keadaan, energi harus dilepaskan. Dikenal sebagai panas laten. Nilai energi aktual untuk perubahan keadaan fisik ini untuk berbagai zat ditangani secara lebih rinci dalam Catatan Energi. 2f (ii) Kurva Pemanasan. Apa yang terjadi pada suhu suatu zat jika dipanaskan dari keadaan padat ke keadaan gas Perhatikan suhu tetap konstan selama perubahan keadaan pelelehan pada temperatur Tm dan mendidih pada suhu Tb. Hal ini karena semua energi yang diserap dalam pemanasan pada suhu ini (pemanasan laten atau enthalpies perubahan keadaan), berlanjut menjadi melemahnya kekuatan antarpartikel (ikatan antarmolekul) tanpa kenaikan suhu. Gain panas sama dengan energi diserap endothermicheat yang dibutuhkan untuk mengurangi kekuatan antarmolekul. . Di antara bagian perubahan keadaan horizontal pada grafik, Anda dapat melihat masukan energi meningkatkan energi kinetik partikel dan menaikkan suhu zat. Lihat bagian 2. untuk penjelasan rinci tentang perubahan negara. Kurva pemanasan merangkum perubahan: Untuk setiap perubahan keadaan, energi harus ditambahkan. Dikenal sebagai panas laten. Nilai energi aktual untuk perubahan keadaan fisik ini untuk berbagai zat ditangani secara lebih rinci dalam Catatan Energi. PANAS KHUSUS PANAS Panas laten untuk perubahan keadaan cairan padat ltgt disebut panas pelepasan fusi khusus (untuk pencairan atau pembekuan). Panas laten untuk negara mengubah gas ltgt cair disebut panas laten yang spesifik dari penguapan (untuk pengembunan, penguapan atau pendidihan) Untuk informasi lebih lanjut tentang panas laten, lihat catatan fisika saya tentang panas laten tertentu Dijelaskan dengan menggunakan teori partikel kinetik gas dan padatan Ini Adalah saat padatan, pada pemanasan, langsung berubah menjadi gas tanpa mencair, DAN gas pada pendinginan melakukan reformasi yang solid secara langsung tanpa terkondensasi pada cairan. Sublimasi biasanya hanya melibatkan perubahan fisik NAMUN tidak selalu sesederhana itu (lihat amonium klorida). Teori dalam hal partikel. Bila padat dipanaskan, partikel bergetar dengan kekuatan yang meningkat dari energi panas tambahan. Jika partikel memiliki cukup energi kinetik getaran untuk sebagian mengatasi kekuatan menarik particleparticle yang Anda harapkan akan meleleh. NAMUN, jika partikel pada titik ini memiliki energi yang cukup pada titik ini yang akan menyebabkan mendidih, cairan TIDAK terbentuk dan padatan berubah langsung menjadi gas. Secara keseluruhan perubahan endotermik. Energi diserap dan dibawa masuk ke sistem. Pada pendinginan, partikel bergerak lebih lambat dan memiliki energi kinetik yang kurang. Akhirnya, ketika energi kinetik partikel cukup rendah, akan memungkinkan kekuatan menarik particleparticle untuk menghasilkan cairan. NAMUN energi mungkin cukup rendah untuk memungkinkan pembentukan langsung dari padatan, yaitu partikel TIDAK memiliki cukup energi kinetik untuk mempertahankan keadaan cair Perubahan eksotermik keseluruhan. Energi dilepaskan dan diberikan ke sekitarnya. Bahkan pada botol suhu kamar kristal yodium padat terbentuk di bagian atas botol di atas padatan. Semakin hangat labanya, semakin banyak kristal terbentuk saat mendingin di malam hari. Jika Anda dengan lembut memanaskan iodium dalam tabung reaksi, Anda akan melihat yodium dengan mudah luhur dan rekristalisasi di permukaan yang lebih dingin di dekat bagian atas tabung reaksi. Pembentukan bentuk beku tertentu melibatkan pembekuan langsung uap air (gas). Frost juga bisa menguap langsung kembali ke uap air (gas) dan ini terjadi pada musim dingin yang kering dan sangat dingin di Gurun Gobi pada hari yang cerah. H 2 O (s) H 2 O (g) (hanya perubahan fisik) Karbon dioksida padat (es kering) terbentuk pada pendinginan gas sampai kurang dari 78 o C. Pada pemanasan, perubahannya langsung berubah menjadi gas yang sangat dingin. Mengembunkan uap air di udara ke kabut, maka penggunaannya dalam efek panggung. CO 2 (s) CO 2 (g) (hanya perubahan fisik) Pada pemanasan dengan kuat pada tabung reaksi, amonium klorida padat putih. Terurai menjadi campuran dua gas amonia tak berwarna dan hidrogen klorida. Pada pendinginan reaksi dibalik dan perbaikan amonium klorida padat di permukaan atas tabung uji yang lebih dingin. Amonium klorida energi panas amonia hidrogen klorida T ini melibatkan perubahan kimia dan fisik dan lebih rumit daripada contoh 1. sampai 3. Sebenarnya kristal amonium klorida ionik berubah menjadi gas amonia dan hidrogen klorida kovalen yang secara alami jauh lebih mudah menguap ( Zat kovalen umumnya memiliki titik leleh dan titik didih yang jauh lebih rendah daripada zat ionik). Gambar partikel cair tidak terlihat di sini, namun model lainnya sepenuhnya berlaku terlepas dari perubahan keadaan yang melibatkan pembentukan cairan. Model partikel GAS dan model partikel SOLID link. HARAP DIPERHATIKAN, Pada tingkat studi yang lebih tinggi. Anda perlu mempelajari diagram fase gls untuk air dan kurva tekanan uap es pada suhu tertentu. Misalnya, jika tekanan uap ambien kurang dari tekanan uap ekuilibrium pada suhu es, sublimasi dapat dengan mudah terjadi. Salju dan es di daerah dingin Gurun Gobi tidak meleleh di Matahari, mereka perlahan-lahan lenyap lenyap 2 h. Lebih lanjut mengenai perubahan panas dalam perubahan fisik negara Perubahan keadaan fisik yaitu gas ltgt cair juga disertai dengan perubahan energi. Untuk melelehkan zat padat, atau mendidih cairan, energi panas harus diserap atau diambil dari lingkungan sekitar, jadi ini adalah perubahan energi endotermik. Sistem dipanaskan untuk efek perubahan ini. Untuk mengembunkan gas, atau membekukan energi panas padat, harus dilepaskan atau diberikan ke sekitarnya, jadi ini adalah perubahan energi eksotermik. Sistem didinginkan untuk mempengaruhi perubahan ini. Secara umum, semakin besar kekuatan antar partikel, semakin besar energi yang dibutuhkan untuk mempengaruhi perubahan keadaan DAN semakin tinggi titik lebur dan titik didih. Perbandingan energi yang diperlukan untuk meleleh atau merebus berbagai jenis zat (Ini lebih untuk siswa tingkat lanjut) Perubahan energi panas yang terlibat dalam perubahan keadaan dapat dinyatakan dalam kJmol zat untuk perbandingan yang adil. Pada tabel di bawah ini 916H mencair adalah energi yang dibutuhkan untuk mencairkan 1 mol zat (rumus massa dalam g). 916H vap adalah energi yang dibutuhkan untuk menguap dengan penguapan atau perebusan 1 mol zat (rumus massa dalam g). Untuk molekul kovalen kecil sederhana, energi yang diserap oleh material relatif kecil untuk meleleh atau menguapkan zat dan semakin besar molekul semakin besar kekuatan antarmolekul. Kekuatan ini lemah dibandingkan dengan ikatan kimia yang menahan atom bersama dalam molekul itu sendiri. Energi yang relatif rendah dibutuhkan untuk meleleh atau mengosongkannya. Zat ini memiliki titik leleh dan titik didih yang relatif rendah. Untuk jaringan 3D berikat kuat mis. (Iii) dan kisi logam ion dan elektron terluar bebas (ikatan eterik), strukturnya jauh lebih kuat secara kontinyu karena ikatan kimia kontinyu di seluruh struktur. Akibatnya, energi yang jauh lebih besar diperlukan untuk meleleh atau menguapkan bahan. Inilah sebabnya mengapa mereka memiliki titik leleh dan titik didih yang jauh lebih tinggi. Jenis ikatan, struktur dan kekuatan yang menarik yang beroperasi Titik lebur K (Kelvin) o C 273 Energi yang diperlukan untuk melelehkan zat Titik didih K (Kelvin) o C 273 Energi dibutuhkan untuk merebus zat 3a. APA YANG TERJADI PADA PARTIKEL KETIKA SOLID DISSOLVES DALAM SOLVEN LIQUID Apa kata-kata SOLVENT, SOLUTE and SOLUTION mean Bila zat padat (zat terlarut) larut dalam cairan (pelarut), campuran yang dihasilkan disebut solusinya. Secara umum: larutan pelarut terlarut Jadi, zat terlarut inilah yang larut dalam pelarut, pelarut adalah cairan yang melarutkan beberapa hal dan solusinya adalah hasil pelarutan sesuatu dalam pelarut. Padat kehilangan semua struktur regulernya dan partikel padat (molekul atau ion) masing-masing sekarang benar-benar bebas satu sama lain dan dicampur secara acak dengan partikel cair asli, dan semua partikel dapat bergerak secara acak. Ini menggambarkan garam larut dalam air, gula larut dalam teh atau lilin larut dalam pelarut hidrokarbon seperti roh putih. Biasanya tidak melibatkan reaksi kimiawi, jadi ini umumnya contoh perubahan fisik. Apapun perubahan volume cairan padat, dibandingkan dengan solusi akhir, UU Konservasi Misa masih berlaku. Ini berarti: massa massa zat terlarut padat dari massa larutan pelarut cair setelah dicampur dan dilarutkan. Anda tidak bisa menciptakan massa atau kehilangan massa. Tapi hanya mengubah massa zat menjadi bentuk lain. Jika pelarut diuapkan. Maka solidnya direformasi mis. Jika larutan garam ditinggalkan untuk waktu yang lama atau dipanaskan dengan lembut untuk mempercepatnya, pada akhirnya bentuk kristal garam, prosesnya disebut kristalisasi. 3b. APA YANG TERJADI TERHADAP PARTIKEL KETIKA DUA KALI SEGALA MIX DENGAN SETIAP APA YANG APA YANG KITA DIKETAHUI KATA BIASA Menggunakan model partikel untuk menjelaskan cairan yang dapat disembuhkan. Jika dua cairan benar-benar mencampur dalam bentuk partikelnya, mereka disebut cairan yang mudah larut karena keduanya larut dalam satu sama lain. Hal ini ditunjukkan pada diagram di bawah dimana partikel benar-benar bercampur dan bergerak secara acak. Prosesnya bisa dibalik dengan distilasi fraksional. 3c. APA YANG TERJADI TERHADAP PARTIKEL KETIKA DUA KALI TIDAK MIX DENGAN SETIAP APA YANG APA YANG DIMAKSUDKAN KATA BIJI MIMPI SENDIRI MENGAPA MATA TIDAK MIX Menggunakan model partikel untuk menjelaskan cairan yang tidak bercampur. Jika kedua cairan itu TIDAK bercampur. Mereka membentuk dua lapisan yang terpisah dan dikenal sebagai cairan tak bercampur, diilustrasikan pada diagram di bawah dimana cairan ungu bawah akan lebih padat daripada lapisan atas cairan hijau. Anda dapat memisahkan dua cairan ini dengan menggunakan corong pemisah. Alasan untuk ini adalah bahwa interaksi antara molekul salah satu cairan saja lebih kuat daripada interaksi antara dua molekul berbeda dari cairan yang berbeda. Misalnya, kekuatan daya tarik antara molekul air jauh lebih besar daripada molekul oiloil atau molekul air minyak, jadi dua lapisan terpisah terbentuk karena molekul air, dalam hal perubahan energi, disukai dengan tetap bertahan. 3d. Bagaimana corong pemisah digunakan 1. Campuran dimasukkan ke dalam corong pemisah dengan stopper dan keran ditutup dan lapisannya tertinggal. 2. Stopper dilepaskan, dan keran dibuka sehingga Anda dapat dengan hati-hati menjalankan lapisan bawah abu-abu terlebih dahulu ke dalam gelas kimia. 3. Ketukan kemudian ditutup kembali, tertinggal dari cairan lapisan atas kuning, sehingga memisahkan dua cairan yang tidak bercampur. Lampiran 1 beberapa gambar partikel sederhana dari ELEMEN, SENYAWA, DAN CAMPURAN GCSEIGCSE pilihan ganda QUIZ pada keadaan gas materi, cairan amp padat Beberapa latihan dasar yang mudah dari sains KS3 QCA 7G quot Model partikel padatan, cairan dan gas Beberapa Pertanyaan Pilihan untuk Revisi Ilmu pada gas , Cairan dan partikel padat, sifat, menjelaskan perbedaan di antara keduanya. Lihat juga untuk perhitungan gas gcse chemistry revisi catatan rinci rinci tentang keadaan materi untuk membantu merevisi catatan kimia kimia igcse igcse notes on states of matter O level chemical revision free detailed notes on states of matter untuk membantu merevisi catatan kimia bebas gcse pada negara bagian matter to help revise O level chemistry free online website to help revise states of matter for gcse chemistry free online website to help revise states of matter for igcse chemistry free online website to help revise O level states of matter chemistry how to succeed in questions on states of matter for gcse chemistry how to succeed at igcse chemistry how to succeed at O level chemistry a good website for free questions on states of matter to help to pass gcse chemistry questions on states of matter a good website for free help to pass igcse chemistry with revision notes on states of matter a good website for free help to pass O level chemistry what are the three states of matter draw a diagram of the particle model diagram of a gas, particle theory of a gas, draw a particle model diagram of a liquid, particle theory of a liquid, draw a particle model diagram of a solid, particle theory of a solid, what is diffusion why can you have diffusion in gases and liquids but not in solids what are the limitations of the particle model of a gas liquid or solid how to use the particle model to explain the properties of a gas, what causes gas pressure how to use the particle model to explain the properties of a solid, how to use the particle model to explain the properties of a solid, why is a gas easily compressed but difficult to compress a liquid or solid how do we use the particle model to explain changes of state explaining melting with the particle model, explaining boiling with the particle model, explaining evaporation using the particle model, explaining condensing using the particle model, explaining freezing with the particle model, how do you read a thermometer wor king out the state of a substance at a particular temperature given its melting point and boiling point, how to draw a cooling curve, how to draw a heating curve, how to explain heatingcooling curves in terms of state changes and latent heat, what is sublimation what substances sublime explaining endothermic and exothermic energy changes of state, using the particle model to explain miscible and immiscible liquids GASES, LIQUIDS, SOLIDS, States of Matter, particle models, theory of state changes, melting, boiling, evaporation, condensing, freezing, solidifying, cooling curves, 1.1 Three states of matter: 1.1a gases, 1.1b liquids, 1.1c solids 2. State changes: 2a evaporation and boiling, 2b condensation, 2c distillation, 2d melting, 2e freezing, 2f cooling and heating curves and relative energy changes, 2g sublimation 3. Dissolving, solutions. miscibleimmiscible liquids Boiling Boiling point Brownian motion Changes of state Condensing Cooling curve Diffusion Dissolving Evaporation Freezing Freezing point Gas particle picture Heating curve Liquid particle picture Melting Melting point miscibleimmiscible liquids Properties of gases Properties of liquids Properties of solids solutions sublimation Solid particle picture GCSEIGCSE multiple choice QUIZ on states of matter gases liquids solids practice revision questions Revision notes on particle models and properties of gases, liquids and solids KS4 Science GCSEIGCSEO level Chemistry Information on particle models and properties of gases, liquids and solids for revising for AQA GCSE Science, Edexcel Science chemistry IGCSE Chemistry notes on particle models and properties of gases, liquids and solids OCR 21st Century Science, OCR Gateway Science notes on particle models and properties of gases, liquids and solids WJEC gcse science chemistry notes on particl e models and properties of gases, liquids and solids CIE O Level chemistry CIE IGCSE chemistry notes on particle models and properties of gases, liquids and solids CCEACEA gcse science chemistry (revise courses equal to US grade 8, grade 9 grade 10) science chemistry courses revision guides explanation chemical equations for particle models and properties of gases, liquids and solids educational videos on particle models and properties of gases, liquids and solids guidebooks for revising particle models and properties of gases, liquids and solids textbooks on particle models and properties of gases, liquids and solids state changes amp particle model for AQA AS chemistry, state changes amp particle model for Edexcel A level AS chemistry, state changes amp particle model for A level OCR AS chemistry A, state changes amp particle model for OCR Salters AS chemistry B, state changes amp particle model for AQA A level chemistry, state changes amp particle model for A level Edexcel A level c hemistry, state changes amp particle model for OCR A level chemistry A, state changes amp particle model for A level OCR Salters A level chemistry B state changes amp particle model for US Honours grade 11 grade 12 state changes amp particle model for pre-university chemistry courses pre-university A level revision notes for state changes amp particle model A level guide notes on state changes amp particle model for schools colleges academies science course tutors images pictures diagrams for state changes amp particle model A level chemistry revision notes on state changes amp particle model for revising module topics notes to help on understanding of state changes amp particle model university courses in science careers in science jobs in the industry laboratory assistant apprenticeships technical internships USA US grade 11 grade 11 AQA A level chemistry notes on state changes amp particle model Edexcel A level chemistry notes on state changes amp particle model for OCR A level chem istry notes WJEC A level chemistry notes on state changes amp particle model CCEACEA A level chemistry notes on state changes amp particle model for university entrance examinations describe some limitations of the particle model for gases, liquids and solidsA follow-up study of children who began school at age 4 (referred to as Year 1 in this study) was conducted to examine the influence of three different preschool models on later school success. These children from an urban school district were studied again in Year 5 as they prepared to leave the primary grades and in Year 6 when they were scheduled to enter fourth grade if not previously retained. The study examined report card grades, retention rates, and special education placement of 160 children at the end of their fifth year in school and 183 children at the end of their sixth year in school. The sample was 96 African American and 54 female, with 75 of the children qualifying for subsidized school lunch and 73 living in single-parent families. Academically, girls surpassed boys at the end of Year 5, and this difference persisted into the next grade level. Children whose preschool experience was more academically directed had been retained less often than peers. No differences attributable to preschool model were found for special education placement. By the end of childrens fifth year in school, there were no significant differences in academic performance of children who had experienced three different preschool models. By the end of their sixth year in school, children whose preschool experiences had been academically directed earned significantly lower grades compared to children who had attended child-initiated preschool classes. Childrens later school success appears to have been enhanced by more active, child-initiated early learning experiences. Their progress may have been slowed by overly academic preschool experiences that introduced formalized learning experiences too early for most childrens developmental status. Introduction In the ongoing debate over education reform designed to improve academic performance of American children, preschools are under increasing pressure to offer instruction in basic academic skills. This trend is especially prevalent in programs that serve low-income children. Compensatory early childhood programs such as Head Start and state-sponsored pre-kindergarten for low-income families and preschoolers with special needs are designed to help children acquire skills needed for later school success. Although the goal of school readiness is widely shared among early childhood educators, parents, and policy makers, the strategies for achieving this goal vary greatly. Fundamental philosophical and political differences in beliefs about the purpose of schooling, value orientations, and cultural priorities are central to the debate on how to best prepare young children for formal schooling (Kessler, 1991). Kindergarten retention rates have increased (e.g. Shepard amp Smith, 1988), perhaps due to the downward shift in curriculum that introduces formal reading and mathematics instruction much earlier. Escalating academic demands in kindergarten have clearly affected preschool programs for even younger children. Goffin (1994) noted a downward movement of the debate between developmental and academic orientations from elementary education to the preschool setting. When preschool was quotreconceptualized as an appropriate beginning for primary schooling (especially for low-income children),quot public school programs for 4-year-olds grew in number (Goffin, 1994, p. 120). Beginning in the 1980s, leading early childhood experts expressed concern about the wisdom of overly didactic, formal instructional practices for young children (e.g. Elkind, 1986 Zigler, 1987). They feared that short-term academic gains would be offset by long-term stifling of childrens motivation and self-initiated learning. Later research suggests that these early concerns were warranted. Compared to children whose kindergarten experience emphasized child-initiated learning, primary-grade teachers rated children from didactic, teacher-centered kindergartens lower in conduct and work-study habits, and perceived them to be more distractible, less willing to follow directions, and less prosocial (Hart, Charlesworth, Burts, amp DeWolf, 1993). Stipek, Feiler, Daniels, and Milburn (1995) also found motivational differences favoring a child-initiated view of early education compared to a more formalized, didactic approach. They cautioned that early academic gains in reading skills associated with didactic instruction of preschoolers quotcome with some costsquot that could have long-term negative effects on achievement. DeVries, Reese-Learned, and Morgan (1991) expressed similar concerns, arguing that temporary benefits of highly didactic approaches with young children cannot be justified in light of possible negative consequences for social development. Today, as Walsh (1989) predicted, the likelihood that children will experience a highly didactic, teacher-centered approach has increased as preschool is absorbed into public schools where a narrowly focused, externally imposed curriculum makes the preschool experience even more like elementary school. Although it was once believed that any well-implemented preschool program would achieve positive results (e.g. Lazar, Darlington, Murray, Royce, amp Snipper, 1982), a growing research base suggests otherwise (see Marcon, 1999, for a review of research on different preschool approaches). Of particular interest in the present study was sustainability of an earlier preschool approachs influence on academic performance. Several researchers have found that later school success declined when the intervention was discontinued. For example, Miller and Dyer (1975) found a drop in school achievement for children who entered a nondidactic program following a direct instruction preschool experience. Similarly, when the highly didactic Direct Instructional System for the Teaching of Arithmetic and Reading (DISTAR) was discontinued after third grade, childrens previously high achievement in reading and mathematics declined (Becker amp Gersten, 1982). Early academic success fostered by a child-initiated approach has been documented by a number of different researchers (e.g. Burts, Hart, Charlesworth, amp DeWolf, 1993 Marcon, 1993, 1999 Weikart, Epstein, Schweinhart, amp Bond, 1978). Some long-term benefits of this approach have been found for school achievement (e.g. Miller amp Bizzell, 1984) as well as for social behavior and general school competence (e.g. Schweinhart amp Weikart, 1997 Schweinhart, Weikart, amp Larner, 1986). Little is known, however, about the long-term effect of early intervention that combines didactic, teacher-centered strategies with child-initiated learning experiences. In the short term, this combination approach has varying outcomes, with some research favoring the strategy, especially for lower functioning children (e.g. Mills, Dale, Cole, amp Jenkins, 1995). A preponderance of the research evidence, however, has failed to support the combination approach (e.g. DeVries et al. 1991 Marcon, 1999 Pfannenstiel amp Schattgen, 1997 Rawl amp OTuel, 1982). Knowing how later school success of these children compares with that of children exposed to other preschool models would be useful in determining the effectiveness of a combination strategy. A second area of interest in the present study involved sex differences in later school success. Academically, studies of low-income children have found that girls did better than boys in pre-kindergarten (e.g. Marcon, 1999), kindergarten (e.g. Burts et al. 1993 Marcon, 1993), and in first grade (e.g. Reynolds, 1989). Boys do notably better in both the short and long term when their early learning experiences have been more child initiated rather than more didactic in nature (e.g. Marcon, 1993 Miller amp Bizzell, 1984). Successful transition between grade levels may also be moderated by sex. Parents and principals believe boys have more difficulty than girls in making the transition from third to fourth grade (Mayfield, 1983). Furthermore, differences in school competence (especially rates of nonpromotion) among African American children may be intensified by negative attitudes and behaviors toward school exhibited as early as fourth grade by African American boys (Rowan, 1989). Further examination of sex differences in later school success of low-income children and possible interaction with preschool model would add to our understanding of the often difficult transition from the primary to the later elementary school grades. The present study provides follow-up data for one cohort of low-income, minority children who had attended two years of school (preschool and kindergarten) prior to entering first grade. These children had experienced one of three different types of preschool: child-initiated, academically directed, or a quotcombinationquot approach. In this earlier quasi-experimental study, Marcon (1999) compared the three different approaches for their effect on childrens development and mastery of basic skills at the end of preschool. Findings indicated that children whose preschool experiences had been child-initiated demonstrated greater mastery of basic skills at the end of preschool than did children in programs where academics were emphasized and skills were directly taught. At the end of preschool, children in the quotcombinationquot model did significantly poorer on all measures except self-help and development of social coping skills compared to children in either the child-initiated or academically directed models. Preschool girls outperformed boys in all areas except gross motor development and playleisure skills. This follow-up study examines the transition from childrens fifth to sixth year in school (third to fourth grade for most of these children). Based on earlier findings for these children and results of other research studies (e.g. Miller amp Bizzell, 1984 Schweinhart amp Weikart, 1997 Schweinhart, Weikart, amp Larner, 1986), it was thought that any difference in later school success attributable to preschool model would favor the child-initiated early learning approach. Children who had experienced quotcombinationquot preschool curricula were expected to be least successful, whereas later school performance of those who had attended didactic, teacher-centered preschools was expected to be intermediary. Sex differences in school achievement favoring girls were expected to persist because boys, in general, do not perform as well in the early years of school (Richardson, Koller, amp Katz, 1986), and African American boys, unlike boys in general, do not typically show a rise in school achievement following the elementary school years (Pollard, 1993). The type of preschool experience was expected to have a greater effect on later school achievement of boys than on girls. Participants Children who began school at age 4 (referred to as Year 1 in this study) were studied again in Year 5 (when they were expected to be in third grade if not previously retained) and Year 6 (when they were expected to be in fourth grade if not previously retained) of their educational experience. This sample of urban students included 160 Year 5 children ( M age 107.6 months, SD 3.9) in 61 schools and 183 Year 6 children ( M age 119.8 months, SD 3.6) in 70 schools. The initial sample had been randomly selected proportional to enrollment of 4-year-olds in subdistricts within the school system. Each subdistrict was represented by at least one classroom for each of the three models studied. This stratified sample was geographically dispersed across the city and was representative of socioeconomic, administrative, and local variations within the school system (see Marcon, 1992, for a description of random selection and stratification procedures used in the original cohort study). This follow-up sample from the original cohort was 96 African American and 54 female. Most children (75) qualified for subsidized school lunch based on low family income, and 73 of the children lived in single-parent families. Data from both Years 5 and 6 were available for a subsample of the children ( n 139) in 64 schools. Subsample children did not differ significantly from the larger follow-up sample in any demographic characteristics. Recovery rate from preschool to fourth grade was 64 of the original sample. Although this attrition rate was high, it was not unexpected, and attrition was comparable across the preschool models, (2) 1.80, p .41. The recovered follow-up sample was not significantly different from the original preschool sample in terms of gender ( p .92), age ( p .82), parent involvement ( p .34), overall adaptive behavior ( p .16), social and work habits ( p .23), or physical development ( p .15) in preschool. Preschool grades of children in the recovered follow-up sample were, however, 3 lower than the original sample ( p .02). Compared to the original preschool sample, the recovered follow-up sample had more African American and fewer White children, (3) 15.34, p .01, who were poorer, (1) 12.60, p lt .001, and more likely to live in single-parent families, (1) 4.83, p .03. These differences were consistent with school districtwide changes in enrollment patterns following pre-kindergarten and kindergarten when children of many middle-class families leave the public school system. At age 4, all children had attended free, full-school-day preschool in the same urban school district, with approximately 84 of the sample having been enrolled in pre-kindergarten and 16 in Head Start. Eligibility for pre-kindergarten was based solely on age and residency, whereas Head Start eligibility had an additional federal requirement of low family income. All preschool teachers of children in this study, both pre-kindergarten and Head Start, held a bachelors degree or higher. Their median pre-kindergarten or Head Start teaching experience was approximately 10 years. As previously classified (see quotMeasures and Proceduresquot section for details), approximately 33 of children in this follow-up sample had attended preschool classes that followed a child-initiated approach, 35 attended academically directed preschool classes, and the remaining 32 had been enrolled in middle-of-the-road preschool classes that combined the other two preschool approaches. No Head Start classes in this school district used an academically directed approach. Kindergarten in this school district was predominantly academic in focus, with all but a handful of teachers indicating a strong belief that academic preparation was a more important goal of kindergarten than childrens socioemotional growth (Marcon, 1990, 1993). All first-grade teachers in this school district emphasized academics, with approximately two-thirds using a highly didactic, academically directed approach (Marcon, 1990). Measures and Procedures Preschool Model. The Pre-K Survey of Beliefs and Practices (see Marcon, 1999, for instrument and details) was used to classify childrens early learning experiences based on five theoretical differences between early childhood models: (1) scope of developmental goals, (2) conception of how children learn, (3) amount of autonomy given to the child, (4) conception of teachers role, and (5) provision of possibilities for learning from peers. Three groupings identified through cluster analysis using Wards method were selected as examples of the divergent preschool models operating in this urban school system. One group was composed of child development-oriented teachers who facilitated learning by allowing children to actively direct the focus of their learning. These child-initiated preschool classrooms were referred to as Model CI. Another group represented more academically oriented teachers who preferred more direct instruction and teacher-directed learning experiences for preschoolers. These academically directed preschool classrooms were referred to as Model AD. The third group represented teachers whose beliefs and practices fell in between the other two opposing models by endorsing a combination approach. These middle-of-the-road preschool classrooms were referred to as Model M. In the original study, accuracy of model classification based upon survey response was affirmed by independent classroom observers, and findings were congruous with other research demonstrating strong consistency between outside raters observations of early childhood instructional activities and teachers self-reported beliefs and practices (e.g. Charlesworth, Hart, Burts, Mosley, amp Fleege, 1993 Hyson, Hirsch-Pasek, amp Rescorla,1990 Kagan amp Smith, 1988 Vartuli, 1999). In the original study, Model CI and Model AD classifications were easily verified by independent classroom observers, but these same observers had some difficulty categorizing Model M practices in several classrooms. Model M teachers appeared to be closer to Model CI in goals but more like Model AD in teacher initiation of activities. Compared to Model CI teachers, the Model M teacher was notably more engaged in leading groups of children in less-individualized activities for longer periods of time. Compared to Model AD teachers, the Model M teacher allowed children greater access to classroom materials, encouraged more peer interaction, and initiated fewer teacher-directed cognitive activities that were not well integrated with other developmental domains. These Model M teachers were not, however, using a Vygotskian approach to foster childrens early learning and development. Model M teachers were best described as professionals who sought to blend notions of child development with their school systems competency-based curriculum. Their basis for doing so was most likely pragmatic. Report Cards. Data were collected from teachers and school records at the end of Year 5 and Year 6. The school districts Elementary School Progress Report (report card) was used to compare childrens classroom performance with the districts expectations for skills mastery. Like many urban school districts, a competency-based curriculum (CBC) was in place throughout most of the school system, and children were expected to demonstrate mastery of specific reading and arithmetic skills before advancing to the next grade level. CBC defined a skill as being mastered when a child could perform it upon request and provided teachers with three mastery assessment tasks for each reading and arithmetic objective (see McClure amp Leigh, 1981, for details of this school systems CBC). For research purposes, Progress Report grades were converted to the standard 5-point numeric scale: 0 F, 1 D, 2 C, 3 B, and 4 A. Each childs overall grade point average (GPA) was calculated. Grades in each of 11 subject areas were also converted to numeric scores: arithmetic, reading, language, spelling, handwriting, social studies, science, art, music, healthphysical education (PE), and citizenship. Citizenship grades provided a global assessment of a childs deportment while attending school. School records and teacher report provided information on the childs eligibility for subsidized school lunch and the number of parents or guardians living at home with the child (scored as 1 or 2). School Competence: Special Education Placement and Retention Year 5. During the primary grades (first, second, and third grades), this school district was more inclined to use retention in grade rather than special education services for children who experienced academic difficulties. By Year 5, less than 1 of this random sample had received special education services, whereas 20 had been retained in grade. No significant differences in special education placement were found for preschool model or sex. Special education placement during the primary grades was not related to family income as measured by eligibility for subsidized school lunch ( p .44) or to the childs living in a single-parent family ( p .43). Boys were more likely to have been retained prior to Year 5 (34) than were girls (10), (1, N 161) 13.97, p lt .001. Similarly, teachers were likely to recommend more boys (23) than girls (11) for retention at the end of Year 5, (1, N 165) 4.28, p .04. Although no significant difference in retention rate attributable to preschool model was found for girls ( p .41), Model AD boys had a significantly lower rate of retention prior to third grade than did boys who had attended other types of preschool, (2, n 71) 7.20, p .03. Overall, fewer children who had attended Model AD preschools had been retained prior to third grade (10), (2, N 161) 5.50, p .06, compared to retention rates of 24 and 26 for Models CI and M, respectively. There were no significant differences attributable to preschool model in teachers recommendations for retention at the end of Year 5 ( p .75). Other demographic factors (family income, single-parent families) that could contribute to retention in grade were examined. Lower-income children were more likely than higher-income children to have been retained prior to third grade, (1, N 160) 7.02, p .01. Although no significant difference in retention rate at the end of Year 5 was found between children who did or did not qualify for subsidized lunch ( p .14), teachers recommended far fewer children who did not qualify for subsidized lunch for retention than was expected statistically. Children who lived in single-parent versus two-parent families did not differ in retention rates prior to Year 5 ( p .18). At the end of Year 5, however, teachers were somewhat less likely to recommend retention for children who were growing up in two-parent families, (1, N 133) 2.44, p .12. Year 6. Because children were of the age to be leaving the primary grades, this school district was now more inclined to recommend special education services for children who experienced academic difficulties, (1, N 139) 5.16, p .02. In Year 6, the number of children who received special education services increased to 8 of the sample. No significant differences in special education placement were found for preschool model or sex. Special education placement following the primary grades was somewhat related to family income, (1, N 166) 2.52, p .11. Only half as many children who did not qualify for subsidized lunch as expected statistically were receiving special education services. Special education placement in Year 6 was not related to growing up in a single-parent family ( p .31). Possibly due to increases in special education placement, teachers recommendations for retention at the end of Year 6 (10) decreased in comparison with retention recommendations made at the end of Year 5 (16). No significant differences were found in recommended retention at the end of Year 6 for preschool model, sex, or family income. Teachers were more likely to recommend children from single-parent families for retention at the end of Year 6 than children living in two-parent families, (1, N 149) 4.25, p .04. Year 5 Report Cards A 3 x 2 (Preschool Model x Sex) analysis of covariance (ANCOVA) was used to test for differential effects of preschool model on childrens grades, sex differences, and possible Preschool Model x Sex interactions at the end of Year 5 in school. The covariate used to control for possible economic differences between children was eligibility for subsidized school lunch (based on family income and size). Although a direct measure of family income would have been a more desirable covariate, it was not available. Eligibility for subsidized school lunch should be highly correlated with family income and is a widely used estimate of family income in public school evaluation research. All reported means have been adjusted for the covariate. Missing scores were not imputed. The academic performance of children who were quoton schedulequot at the end of Year 5 (third grade), as well as performance of children who had been retained prior to third grade, was examined in this follow-up study. Preschool Model. No significant main effect for preschool model was found in Year 5 overall GPA or any specific subject area for either quoton schedulequot or quotretainedquot children. A statistical trend toward significant differences between preschool models was found for Year 5 citizenship grades, F (2, 153) 2.66, p .07. Overall, Model AD children received citizenship grades that were 6 and 19 lower than Model CI and Model M children, respectively. Citizenship grades reflect childrens deportment in school. At the end of Year 5, children from the three different preschool models were performing academically at a comparable level. Teachers did, however, see the school behavior of children who had attended academically directed preschools as being notably poorer than that of peers. Sex Differences. A significant sex difference was found in overall Year 5 GPA, F (1, 153) 4.05, p .05, with girls earning a 10 higher GPA than boys. Effect size for this difference was moderate (.34). As seen in Figure 1, girls earned higher grades in each of the 11 subject areas. A significant difference was found for citizenship grades, F (1, 153) 12.26, p .001, with teachers rating girls school behavior 24 quotbetterquot than that of boys. Effect size for the difference in citizenship grades was large (.58). At the end of Year 5, girls were outperforming boys in school. Interactions. No significant Preschool Model x Sex interactions were found for overall GPA or any of the 11 subject areas for either quoton schedulequot or quotretainedquot children. No statistical trends toward significant group differences were found. The smallest gap between performance of boys and girls appeared for Model M children (boys GPA was only 2 lower than girls GPA). In four subject areas (language, spelling, art, and music), Model M boys received somewhat higher grades than did Model M girls. A similar pattern was not present in the other two preschool models. Year 5 Summary. For children who had attended preschool and kindergarten prior to entering first grade, there was no significant difference in academic performance attributable to preschool model at the end of childrens fifth year in school. Girls outperformed boys in school, but this difference was less noticeable among children who had attended quotcombinationquot preschool classes. Teachers rated boys school behavior lower than girls behavior. Compared to peers, children who had attended academically directed preschool classes also were rated lower in behavior compared to peers at the end of their fifth year in school. Year 6 Report Cards Preschool Models. As shown in Table 1 and Figure 2, a trend towards statistical significance between preschool models was found in Year 6 overall GPA ( p .07). GPA for Model CI was 4 higher than Model M and 14 higher than Model AD. The difference between Models CI and AD was moderate (effect size .38). In all subject areas except music, Model AD children displayed the lowest grades of the three preschool models. In all but three subject areas (language, social studies, and music), Model CI had the highest grades compared to peers who had other types of preschool experiences. Science grades of Model M children equaled those of Model CI. Post hoc Tukeys HSD ( p lt .01) indicated that Models CI and M earned significantly higher healthPE grades than did Model AD. By the end of Year 6, academic performance of children who had attended academically directed preschool classes was beginning to decline. Although not statistically significant, their school behavior continued to be rated somewhat lower than that of peers Model AD citizenship grades were 14 and 9 lower than Models CI and M, respectively. Table 1 Year 6 Report Cards: Preschool Model (PM) and Sex Differences (GB) Note: Means adjusted for family income (eligibility for subsidized lunch) covariate. Sex Differences. As shown in Table 1 and Figure 3, a significant sex difference was found in overall GPA ( p .003), with girls receiving 13 higher grades than boys. Effect size for this difference was moderate (.44). Girls earned higher grades in all of the 11 subject areas except art. These differences were statistically significant for reading, spelling, social studies, and citizenship. Effect sizes for sex differences were moderate to large, with the greatest effect size seen in citizenship grades (.76). A trend toward statistically significant differences between girls and boys was found in four other subject areas: arithmetic, language, science, and healthPE. At the end of Year 6, girls continued to outperform boys in school. Interactions. No significant Preschool Model x Sex interactions were found for overall GPA or any of the 11 subject areas in Year 6. A possible interaction between preschool model and sex was found for Year 6 music grades, F (2, 153) 2.59, p .08. Unlike other boys, Model AD boys earned somewhat higher grades in music (6) than did Model AD girls. However, at the end of childrens sixth year in school, the smallest gap between school performance of boys and girls appeared for Model CI children. The GPA of Model CI boys was only 9 lower than that of girls, whereas a 16 and 14 difference between girls and boys GPA was found for Models M and AD, respectively. Year 6 Summary. School performance of those who had attended academically directed preschool classes was beginning to decline by the end of childrens sixth year in school. Girls still outperformed boys in school, but this difference was now less noticeable among children who had attended child-initiated preschool classes. Teachers continued to rate school behavior of boys lower than that of girls. Although no significant differences attributable to preschool approach were found in behavior at the end of the sixth year in school, teachers continued to rate behavior of children with academically directed preschool experiences somewhat lower than their peers. Transition from Year 5 to Year 6 A 3 x 2 x 2 (Preschool Model x Sex x Year) repeated measures multiple analysis of covariance (MANCOVA) with year as the repeated variable was used to test for differential effects of preschool model on childrens grades, sex differences, and possible Preschool Model x Sex interactions across time (Year 5 to Year 6). As with previous analyses, the covariate used to control for possible influence of economic differences between children was eligibility for subsidized school lunch. Missing scores were not imputed. Main Effect for Year. Although childrens grades generally dropped as they left the primary grades and entered the later elementary school grades, no significant main effect for year was found in the subsamples overall GPA, F (1, 132) .88, p .35. Analyses of each subject area yielded only one significant main effect for year subsample childrens grades in language decreased 8 from Year 5 to Year 6, F (1, 131) 4.78, p .03. Effect size for this difference was small (.16). Interactions across Years. Of greater interest in childrens transition from the primary to the later elementary school grades was how an earlier preschool model or childrens sex or both might differentially affect school performance across years. Therefore, two-way interactions (Preschool Model x Year Sex x Year) and the possibility of a three-way interaction (Preschool Model x Sex x Year) were examined more closely. As shown in Table 2 and Figure 4, there was a significant interaction between preschool model and year for GPA ( p .02). The GPA of Model CI children increased 6, while GPA decreased 4 and 8 for Models M and AD, respectively. A similar pattern of Model CI increases and Models M and AD decreases was found in 6 of the 11 subject areas: reading, language, spelling, science, healthPE, and citizenship. In an additional three subject areas (arithmetic, art, and handwriting), Model CI grades either remained constant or increased. Model M grades increased in only one subject area, music. Model AD grades increased in only one subject area, handwriting. Finally, all three preschool models showed a drop in childrens social studies grades from Year 5 to Year 6. Table 2 ANCOVA Interactions for Preschool Model and Sex: Year 5 to Year 6 As shown in Table 2, four subject area Preschool Model x Year interactions were significant: arithmetic, reading, spelling, and healthPE. Statistical trends toward significant interactions were found for language and citizenship. Only one Sex x Year interaction was found to be significant. Girls grades in spelling increased 3, and boys grades decreased. A somewhat similar pattern was found for healthPE grades ( p .07), with boys grades decreasing 6 and girls grades remaining constant in healthPE. This Sex x Year interaction pattern, however, was not typical of other subject areas. Figure 5 shows increases or decreases in boys and girls grades across years for each preschool model. As seen in Table 2, citizenship was the only subject area to show a significant three-way interaction between preschool model, childrens sex, and year ( p .05). Model CI boys and girls had similar increases in citizenship grades across years (8 and 6, respectively). The overall decrease in Model M citizenship grades was due primarily to a 19 drop in boys grades Model M girls decreased only slightly (2). Citizenship grades of Model AD boys increased 26, while girls citizenship grades decreased 7. The source of boys improvement was due primarily to fewer failing Year 6 citizenship grades among boys whose school deportment had been previously unacceptable. Even with this improvement, however, Model AD boys remained 11 behind Model CI boys in Year 6 citizenship grades. And, although improved, these Year 6 citizenship grades for Model AD boys still remained lower than citizenship grades of girls (33, 32, and 18 lower compared to Models CI, M, and AD girls, respectively). Discussion As predicted, preschool model did have an influence on childrens later school achievement. Children whose preschool experience was child initiated faired better than peers in the transition from the primary to the later elementary school grades. Not only were their overall grades following the transition significantly higher, their school performance improved or held constant in all but two subject areas (music, social studies) despite increased academic demands of the next grade level. Contrary to predictions, children from preschool classes where teachers had attempted to combine distinctive approaches were performing better in school than expected. By the end of their fifth year in school, they had quotcaught upquot to classmates from other preschool models. Relative to peers, the position of children with combination approach preschool experiences was intermediary following the transition. Findings regarding later school success were somewhat mixed for children who had more didactic, academically directed preschool experiences. Although fewer of these children had been retained during the primary grades, children from this preschool model were least successful in making the transition to the later elementary school grades. Grades of children from academically directed preschool classrooms declined in all but one subject area (handwriting) following the Year 6 transition. What contributed to the lower rates of retention prior to third grade among children whose earlier preschool experiences had been academically directed One possibility is greater continuity between the preschool experience and what children encountered in this public schools kindergartens and primary grades. After preschool, these children were likely to enter a moderately academic kindergarten with more formal instruction practices in reading and arithmetic (Marcon, 1993). In fact, only 20 would have experienced a more socioemotional-oriented kindergarten in this school district, and virtually none of the first-grade classrooms that children entered would have resembled less academically focused preschools. Model AD children most likely had an easier transition to the primary grades. A second possibility involves family-related influences on early grade retention. Lower-income children in this follow-up study were more likely to have been retained prior to third grade. Children eligible for Head Start came from the lowest-income homes and in the setting of this study were likely to be growing up in single-parent families. No children eligible for Head Start in this study were enrolled in Model AD classes. Thus, lower retention of Model AD children could be more related to family income factors than to type of preschool experience. A third possibility is that grade-level placements may not fully reflect academic performance in a competency-based system of promotion that emphasizes basic reading and arithmetic skills. If mastery of critical skills in these two subjects was not demonstrated, children were automatically retained regardless of their performance in other subject areas. Likewise, children who demonstrated mastery of critical reading and arithmetic objectives were able to advance regardless of performance in other subject areas. Meeting basic competency requirements of the primary grades may not be sufficient to sustain later academic performance when quotpulling it all togetherquot requires more than just quotadding up the piecesquot children have acquired along the way. Children with academically directed preschool experiences may have missed out on the more integrative experiences of peers in other preschool models. Future research to investigate each of these possibilities is needed. By the end of the primary grades, there was little difference in the academic performance of children who had experienced three different preschool models. This finding was consistent with the developmental assumption that, by the end of third grade, most children will have attained the basic academic skills. Earlier limitations associated with a combination approach had been overcome, and children were generally academically comparable and on quoteven footingquot when they entered the transition to the later elementary school grades. What happened on the other side of this transition Why did academic performance of children from academically directed preschool classes begin to decline The difference between their school grades and those of children from child-initiated preschools was not just statistically significant151the 14 difference in grades was of practical significance with children differing by more than a third of a standard deviation in overall grades. Perhaps the answer can be found in new demands characteristic of the later elementary school grades. Through the primary grades, children are learning to read. An academically directed approach typically emphasizes the act of reading over comprehension. Beginning in fourth grade, children are reading to learn comprehension is critical. In fourth grade, they encounter more abstract concepts that do not necessarily match up with their everyday experiences. Additionally, fourth-grade teachers expect children to be more independent in the learning process, to assume more responsibility for their learning, and to show greater initiative. Perhaps teachers foster this independence by stepping back somewhat and shifting their instructional approach to be less didactic. It is at this point that motivation and self-initiated learning become crucial for childrens later school success. This is the point at which Elkind (1986) and Zigler (1987) worried that short-term academic gains produced by overly didactic, formal instructional practices for young children would be offset by long-term stifling of childrens motivation. Important lessons about independence and self-initiative are being learned in the early childhood years. Overly teacher-directed approaches that tell young children what to do, when to do it, and how to do it most likely curtail development of initiative during the preschool years. According to developmentalist Constance Kamii (1975, 1984), such an approach produces passive students who wait to be told what to think next. Therefore, it is not really surprising that children whose preschool experience may have curtailed initiative would find the transition to the later elementary school grades more difficult. The foundation of critical thinking may be found in early childhood experiences that foster curiosity, initiative, independence, and effective choice. As predicted, earlier sex differences in school achievement favoring girls persisted both at the end of the primary grades and following the transition to the later elementary school years. Going into the transition, the smallest gap between boys and girls academic performance was seen among children who had attended preschool classes where teachers used a quotcombinationquot approach. On the other side of the transition, the smallest gap between the sexes was seen in children who had child-initiated preschool experiences. When academic demands increased, boys whose earliest school experiences involved active, self-initiated learning appeared to be better able to meet these new demands. Although sex differences did not, as predicted, moderate the effect of preschool model across time, the closing of the academic gap between boys and girls following the primary grades was interesting. African American boys do not typically follow the academic pattern of boys in general by surpassing girls following the elementary school years. Might the boys in this predominantly African American sample whose preschool experience was active and child initiated break the pattern and pull ahead of girls, or at least stay close to girls, at the next major educational transition Miller and Bizzells findings (1984) suggest that this outcome is a distinct possibility. And, if so, what is the underlying mechanism by which to account for such a possibility How do cultural factors interact with and moderate the influence of various preschool models The passivity required of children in an overly academically directed approach may be especially difficult for young African American boys. In the preschool years, girls earlier maturation may have allowed them to better process the verbal instruction typical of didactic, academically directed instruction, whereas boys generally slower rate of neurological development may have required a more active, quothands onquot approach found in nondidactic, child-initiated early learning experiences. Lessons learned in the preschool years assuredly carry over into childrens later school careers. The next academic transition, when children leave elementary school, will be especially interesting for understanding sex differences in academic performance of these low-income children. Caution is warranted when interpreting this studys findings. First, and foremost, it is important to remember that the quasi-experimental design used in this research does not establish causality. Although parents did not choose their childs teacher or preschool model, neither did the researcher randomly assign children to preschool model at the beginning of this longitudinal study. This was a field study reflecting typical educational practices where children attend their neighborhood school. Second, because the research design is correlational, other intervening variables between preschool and fourth grade most likely contribute to these findings. For example, schools attended, as well as teachers and classmates, undoubtedly affect childrens later school achievement. Additionally, the influence of family characteristics shown to positively affect educational outcomes of African American children (Luster amp McAdoo, 1996) were not adequately examined in this study of intact groups. Only effects of family income and number of parents were investigated. Future research would be strengthened by greater attention to other family characteristics, such as parental beliefs, that are known to influence childrens development (Sigel, 1985). Third, the follow-up sample did differ somewhat from the original in that it consisted of more minority children who were poorer and more likely to live in single-parent families than the sample originally studied. This difference, along with high attrition, was expected in a city where middle-class children often leave the public school system after kindergarten and children from highly mobile, lower-income families often relocate to a neighboring state. Because policy makers were interested in action research that could benefit children enrolled in their own school district, children who left this school system were not followed. Data from those who left the public schools would be interesting to examine. However, it is unlikely that these new data would have altered findings regarding the influence of preschool model because approximately equal numbers of children from each model were lost. Finally, use of individual children as the statistical unit of analysis, rather than school or classroom means, could limit generalizability of findings due to potential interdependence of grades for children in the same classroom. Unfortunately, even nested analysis of potentially nonindependent observations does not guarantee that statistical assumptions of independence of error will be met (Hopkins, 1982). The large number of schools (and hence of teachers) in this follow-up study reduces the possible effect of any particular teachers grading practices on these findings. Concern about interdependence of grades assigned to children in the same classroom is also somewhat reduced by the competency-based grading system used in this school district. It is important to remember that the large number of schools and teachers sampled in this study enhances, but does not guarantee, generalizability of this studys findings. Childrens later school success appears to be enhanced by more active, child-initiated learning experiences. Their long-term progress may be slowed by overly academic preschool experiences that introduce formalized learning experiences too early for most childrens developmental status. Pushing children too soon may actually backfire when children move into the later elementary school grades and are required to think more independently and take on greater responsibility for their own learning process. References Becker, Wesley C. amp Gersten, Russell. (1982). A follow-up of follow through: The later effects of the direct instruction model on children in fifth and sixth grades. American Educational Research Journal, 19 (1), 75-92. EJ 271 993 . Burts, Diane C. Hart, Craig, H. Charlesworth, Rosalind amp DeWolf, Michele. (1993). Developmental appropriateness of kindergarten programs and academic outcomes in first grade. Journal of Research in Childhood Education, 8 (1), 23-31. EJ 493 673 . Charlesworth, Rosalind Hart, Craig H. Burts, Diane C. Mosley, Jean amp Fleege, Pamela O. (1993). Measuring the developmental appropriateness of kindergarten teachers beliefs and practices. Early Childhood Research Quarterly, 8 (3), 255-276. EJ 474 784. DeVries, Rheta Reese-Learned, Halcyon amp Morgan, Pamela. (1991). Sociomoral development in direct-instruction, eclectic, and constructivist kindergartens: A study of childrens enacted interpersonal understanding. Early Childhood Research Quarterly, 6 (4), 473-517. EJ 441 873 . Elkind, David. (1986). Formal education and early childhood education: An essential difference. Phi Delta Kappan, 67 (9), 631-636. EJ 337 505 . Goffin, Stacie G. (1994). Curriculum models and early childhood education: Appraising the relationship. New York: Merrill. Hart, Craig H. Charlesworth, Rosalind Burts, Diane C. amp DeWolf, Michele. (1993, March). The relationship of attendance in developmentally appropriate or inappropriate kindergarten classrooms to first and second grade behavior. Poster session presented at the biennial meeting of the Society for Research in Child Development, New Orleans, LA. Hopkins, Kenneth D. (1982). The unit of analysis: Group means versus individual observations. American Educational Research Journal, 19 (1), 5-18. EJ 271 990 . Hyson, Marion C. Hirsch-Pasek, Kathy amp Rescorla, Leslie. (1990). The classroom practices inventory: An observational instrument based on NAEYCs guidelines for developmentally appropriate practices for 4- and 5-year-old children. Early Childhood Research Quarterly, 5 (4), 475-494. EJ 423 540 . Kagan, Dona M. amp Smith, Kenneth. (1988). Beliefs and behaviours of kindergarten teachers. Educational Research, 30 (1), 26-35. Kamii, Constance. (1975). One intelligence indivisible. Young Children, 30 (4), 228-238. EJ 121 221 . Kamii, Constance. (1984). Autonomy: The aim of education envisioned by Piaget. Phi Delta Kappan, 65 (6), 410-415. EJ 293 135 . Kessler, Shirley A. (1991). Alternative perspectives on early childhood education. Early Childhood Research Quarterly, 6 (2), 183-197. EJ 431 699 . Lazar, Irving Darlington, Richard Murray, Harry Royce, Jacqueline amp Snipper, Ann. (1982). Lasting effects of early education: A report from the Consortium for Longitudinal Studies. Monographs of the Society for Research in Child Development, 47 (2-3, Serial No. 195). EJ 266 057 . Luster, Tom, amp McAdoo, Harriette. (1996). Family and child influences on educational attainment: A secondary analysis of the HighScope Perry Preschool data. Developmental Psychology, 32 (1), 26-39. EJ 524 920. Marcon, Rebecca. (1990). Early learning and early identification: Final report of the three year longitudinal study. Washington, DC: District of Columbia Public Schools. ED 331 934 . Marcon, Rebecca. (1992). Differential effects of three preschool models on inner-city 4-year-olds. Early Childhood Research Quarterly, 7 (4), 517-530. EJ 458 104 . Marcon, Rebecca. (1993). Socioemotional versus academic emphasis: Impact on kindergartners development and achievement. Early Child Development and Care, 96, 81-91. EJ 478 144 . Marcon, Rebecca. (1999). Differential impact of preschool models on development and early learning of inner-city children: A three cohort study. Developmental Psychology, 35 (2), 358-375. EJ 582 451 . Mayfield, Margie I. (1983). Orientation to school and transitions of children between primary grades. Alberta Journal of Educational Research, 29 (4), 272-284. EJ 292 101 . McClure, Larry, amp Leigh, J. (1981). A sampler of competency-based education at its best. In Ruth S. Nickse amp Larry McClure (Eds.), Competency-based education: Beyond minimum competency testing (pp. 89-94). New York: Teachers College Press. ED 206 675 . Miller, Louise B. amp Bizzell, Rondeall P. (1984). Long-term effects of four preschool programs: Ninth- and tenth-grade results. Child Development, 55 (4), 1570-1587. EJ 305 776 . Miller, Louise B. amp Dyer, Jean L. (1975). Four preschool programs: Their dimensions and effects. Monographs of the Society for Research in Child Development, 40 (5-6, Serial No. 162). EJ 138 519 . Mills, Paulette E. Dale, Philip S. Cole, Kevin N. amp Jenkins, Joseph R. (1995). Follow-up of children from academic and cognitive preschool curricula at age 9. Exceptional Children, 61 (4), 378-393. EJ 497 634 . Pfannenstiel, Judy, amp Schattgen, Sharon F. (1997, March). Evaluating the effects of pedagogy informed by constructivism: A comparison of student achievement across constructivist and traditional classrooms. Paper presented at the annual meeting of the American Educational Research Association, Chicago. Pollard, Diane S. (1993). Gender, achievement, and African-American students perceptions of their school experience. Educational Psychologist, 28 (4), 341-356. Rawl, Ruth K. amp OTuel, Frances S. (1982). A comparison of three prereading approaches for kindergarten students. Reading Improvement, 19 (3), 205-211. EJ 269 746 . Reynolds, Arthur J. (1989). A structural model of first-grade outcomes for an urban, low socioeconomic status, minority population. Journal of Educational Psychology, 81 (4), 594-603. EJ 404 602 . Richardson, Stephen A. Koller, Helene amp Katz, Mindy. (1986). Factors leading to differences in the school performance of boys and girls. Journal of Developmental and Behavioral Pediatrics, 7 (1), 49-55. Rowan, Joseph L. (1989). The effect of gender on non-promotion of Black males. Unpublished manuscript. ED 313 456 . Schweinhart, Lawrence J. amp Weikart, David P. (1997). The HighScope preschool curriculum comparison study through age 23. Early Childhood Research Quarterly, 12 (2), 117-143. EJ 554 350 . Schweinhart, Lawrence J. Weikart, David P. amp Larner, Mary B. (1986). Consequences of three preschool curriculum models through age 15. Early Childhood Research Quarterly, 1 (1), 15-45. EJ 334 891 . Shepard, Lorrie A. amp Smith, Mary Lee. (1988). Escalating academic demand in kindergarten: Counterproductive policies. Elementary School Journal, 89 (2), 135-145. EJ 382 617 . Sigel, Irving E. (1985). Parental belief systems: The psychological consequences for children. Hillsdale, NJ: Erlbaum. Stipek, Deborah Feiler, Rachelle Daniels, Denise amp Milburn, Sharon. (1995). Effects of different instructional approaches on young childrens achievement and motivation. Child Development, 66 (1), 209-223. EJ 501 879 . Vartuli, Sue. (1999). How early childhood teacher beliefs vary across grade level. Early Childhood Research Quarterly, 14 (4), 489-514. EJ 631 458 . Walsh, Daniel J. (1989). Changes in kindergarten: Why here Why now Early Childhood Research Quarterly, 4 (3), 377-391. EJ 402 845 . Weikart, David P. Epstein, Ann S. Schweinhart, Lawrence J. amp Bond, James T. (1978). The Ypsilanti preschool curriculum demonstration project: Preschool years and longitudinal results (Monographs of the HighScope Educational Research Foundation, 4). Ypsilanti, MI: HighScope Press. ED 156 756 . Zigler, Edward. (1987). Formal schooling for four-year-olds No. American Psychologist, 42 (3), 254-260. EJ 355 124. Author Information Rebecca A. Marcon, Ph.D. is a developmental psychologist and a professor of psychology at the University of North Florida. She received her B.A. in psychology from California State University-Fullerton and her M.A. from the University of California, Los Angeles. After working as a school psychologist in the barrios of east Los Angeles, she left California to pursue her Ph.D. in developmental psychology at Louisiana State University. Since completing her Ph.D. she has been a faculty member in the Departments of Psychology at Clemson University, Davidson College, and the University of North Florida. She was also a senior research associate in the District of Columbia Public Schools where she initiated an ongoing longitudinal study of early childhood educational practices. Her research interests include social and language development, early intervention, and public policy. She continues to serve young children and families in the District of Columbia Public Schools as a researcher and consultant. Dr. Marcon also is actively involved with Head Start programs serving young children in northeast Florida. She is a member of the Early Childhood Research Quarterly Editorial Board and serves as a Research in Review Editor for Young Children. Rebecca A. Marcon, Ph.D. Department of Psychology University of North Florida 4567 St. Johns Bluff Road, South Jacksonville, FL 32224-2673 Office Bldg. 39-4072 Telephone: 904-620-2807 Fax: 904-620-3814 Email: rmarconunf.edu This article has been accessed 71,587 times through June 1, 2007.
Mql4-forex-factory
Bergerak-rata-rata-manajemen risiko