A. Materi

Gaya Sentripetal

Sebuah gaya yang menyebabkan gerak di jalur yang melengkung disebut gaya sentripetal. Gerak melingkar beraturan adalah contoh dari gaya sentripetal. Hal ini dapat dilihat dalam orbit bulan mengelilingi bumi, tegangan pada tali dalam permainan tali bola, atau roller coaster. Dituliskan dengan persamaan :

F s=m .v2

R (1)

Dengan : Fs = Gaya Sentripetal (N)

m= massa bumi/planet (Kg)

R = Jari-jari lintasan gerak (m)

v = Kecepatan (m/s)

Menentukan Massa Bumi

Massa Bumi dapat ditentukan berdasarkan persamaan (2.2). Mengingat percepatan gravitasi di permukaan bumi g= 9,8 m/s2, jari-jari bumi R= 6,38x106 m dan konstanta gravitasi G= 6,67u10-11Nm2/kg2, maka:

g=G Mr2 , maka :

M= gr2

G(2)

Dengan : g = Percepatan Gravitasi (m/s2)

M= massa bumi/planet (Kg)

r = Jarak antara pusat bumi dengan titik yang ditentukan (m)

G = Konstanta Gravitasi (N.m2Kg-2)

Orbit Satelit Bumi

Suatu benda yang bergerak mengelilingi benda lain yang bermassa lebih besar dinamakan satelit, misalnya bulan adalah satelit bumi. Sekarang banyak satelit buatan diluncurkan untuk keperluan komunikasi, militer, dan riset teknologi. Satelit-satelit yang bergerak dengan orbit melingkar (hampir berupa lingkaran) dan berada pada jarak r dari pusat bumi, maka kelajuan satelit saat mengorbit Bumi dapat dihitung dengan menyamakan gaya gravitasi dan gaya sentripetalnya. Untuk menghitung kecepatan satelit dapat digunakan dua cara, yaitu :

a. Menghitung kecepatan satelit menggunakan hukum gravitasi

LEMBAR KERJA SISWA

LKS-02/X-2/GP/Kecepatangeraksatelit

b. Menghitung kecepatan satelit menggunakan gaya sentrifugal

B. Tujuan Penyelidikan :

1. Mengamati fenomena dengan menggunakan indera.2. Menanya/merumuskan masalah berdasarkan fenomena yang diberikan.3. Mencoba mencari materi pada sumber belajar (buku/internet). Mencoba mendiskusikan & mengeksplorasi

data dan informasi tentang satelit geostasioner (kegunaan, kemanpuan, kedudukan, dan kecepatan geraknya) secara berkelompok

4. Menalar/menghubungkan kedudukan, kemampuan, dan kecepatan gerak satelit berdasarkan data dan in-formasi hasil eksplorasi dengan menerapkan hukum Newton.

5. Menyimpulkan pneyelidikan berdasarkan fenomena dan materi yang didapat.6. Mengaitkan materi ajar dengan lingkungan kehidupan sehari – hari.

C. Prosedur Penyelidikan:

1. Amati fenomena fisika yang didemonstrasikan (video), tulislah apa yang Anda amati !Hal yang Anda amati:................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

2. Rumuskan pertanyaan berdasarkan fenomena yang Anda lihat !Pertanyaan : ................................................................................................................................................................................................................................................................................................Hipotesis / Jawaban Sementara berdasarkan pertanyaan yang kalian berikan : ................................................................................................................................................................................................................................................................................................................................................................................................................................................

3. Mencoba mendiskusikan secara berkelompok & mengeksplorasi data dan informasi melalui sumber belajar

tentang :-revolusi tiap planet di tata surya- perbedaan laju planet & laju satelit- Satelit Geostasioner (kegunaan, kedudukan, dan kecepatan geraknya)

Jawaban :........................................................................................................................................

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4. Hubungkan kedudukan, kemampuan, dan kecepatan gerak satelit berdasarkan data dan informasi hasil eksplorasi dengan menerapkan hukum Newton ! (menurunkan persamaan kecepatan gerak satelit berdasarkan hukum Newton) Jawaban :

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5. Menarik kesimpulan berdasarkan hubungan tersebut !

Kesimpulan :................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

6. Soal : a. Apabila satelit 2 memiliki jarak 16.000.000 dan satelit 1 memiliki jarak 4.000.000 meter dari

Bumi, berapakah perbandingan antara kecepaatan satelit 1 dan 2? b. Massa suatu planet adalah 100.000.000.000 Kg. Jika satelit diletakkan pada jarak 1.000.000 meter dari

planet tersebut. Hitunglah Kelajuan satelit tersebut ! c. Massa suatu planet adalah 500.000.000.000 Kg. Jika satelit diletakkan pada jarak 5.000.000 meter dari

planet tersebut. Hitunglah Kelajuan satelit tersebut !Penyelesaian :1. ........................................................................................................................................................................................................................................................................................................................................................................................................................................

Yg Anda Amati Materi

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3. ........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

7. Mengaitkan materi dengan kehidupan sehari-hariKaitan Materi Ajar dengan Kehidupan Sehari-hari :................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

8. Tuliskan pesan/kesan nilai karakter yang Anda peroleh pada pembelajaran ini:................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................