Orbits (Also seen in GCSE Physics 3)

For anything to stay in orbit it requires two things:

*A centripetal force, caused by the gravitational force acting between the object orbiting and the object being orbited

*To be moving at a high speed

We now know equations for calculating the centripetal force of an object moving in a circle of radius r AND for calculating the gravitational force between two masses separated by a distance of r.

Centripetal force at distance r: or or

Gravitational force at distance r:

These forces are equal to each other, since it is the force of gravity causing the centripetal force.

From these we can calculate many things about an orbiting object:

The speed needed for a given radius

The time of orbit for a given radius