Let's make a solar system

                 黃色圓盤代表太陽,綠色圓盤代表月球,淺藍色圓盤代表行星(地球);連著圓盤淺紅色的直線代表速度的大小及方向;太陽,月球,行星三者以萬有引力相互吸引:     
1.首先按start,物體開始運動.   
2.若要觀察軌跡,按strobo(停止stop,重新設定reset)    
3.reset後,可以用指標改變速度的大小及方向.   
4.嘗試改變不一樣的大小及方向,並觀察其軌跡,想一想為什麼會這樣?    
5.什麼樣的速度(大小及方向)會有圓形的軌道(橢圓形,?物線的軌道)?  
6.什麼樣的速度(大小及方向)會造成行星?離軌道?    
7.什麼樣的速度(大小及方向)會使行星被太陽吸入?

How to play

The yellow disk is a sun in a solor system. The light blue disk is a planet and the green disk is a moon. The short pink lines starting at the each disks are the velocitys. The sun, the planet and the moon attract each other by universal gravitation.
First, click the start button. These disks start moving. If you drag the pointer near each disk, you can change the velocity and the position.
Next, click the Strobo button. You can see the orbit line of each disks. The orbit lines can erase by clicking Start button. If you click the Reset button, you can set the situation initial.

This simulation is calculated by 4th order Runge-Kutta method.
You can get the sorce code of the solar system here.

Copyright 1997 KATO Noriyoshi (norimari@mxb.mesh.ne.jp)

Chinese By 中文注釋:  莊  文  吉 Chuang,Wen-Jye

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