There are two space ships in circular motion (under the same gravitation field/same speed). Suppose you can control the second space ship. You can click the button to change the velocity (in forward/backward/left/right) directions. Each click will change the same ammount of speed dv (dv can be change by slider). Default dv=2.5 and you can fire the button 10 times. If you double dv, then you can only fire 5 times. (If you reduced dv to half, then you can fire 20 times).

Virtual Physics laboratory Original URL

Fu-Kwun Hwang, Dept. Of Physics, National Taiwan Normal University.