Calculating the Force Opposing Gravity in Orbital Simulations

[bkelly]

I am writing a program to do some orbital simulations. For ease of conversation, let's start with the sun and the earth. If the Earth were standing still, the sun would pull it in quite rapidly. As the Earth is moving at about 1.47 kilometers per second, that movement creates a force opposing the suns gravity. How do I calculate that force?

 

[atom888]

v^2/r ?

 

[LURCH]

Quick and dirty way: look up the Sun's gravitational force on the Earth (the two forces are in equilibrium, so they are roughly the same amount of "force").