# Work in space

1. Sep 30, 2008

### MrPickle

Do you need energy to move things in space because;

Work = Force x Distance and the Force = Mass x Gravitational Field Strength but there's no gravity in space so the force will be always be 0?

2. Sep 30, 2008

### mgb_phys

Correct, if you are moving them in a uniform gravitational field. So either in deep space away from any objects or in an orbit at the same distance from an object.

It does take energy to move them from eg. low earth orbit to the moon. The Earth's gravity doesn't suddenly stop at the top of the atmosphere.

3. Sep 30, 2008

### rcgldr

Work doesn't required gravity. Work still equals force times distance, and the change in kinetic energy of an object will be equal to the work done. You do need a frame of reference in order to assign values to distance and velocity.

Rockets in space are a special case: since their engines only produce internal work, momentum is conserved. The sum of mass times velocity for spent fuel expelled by a rocket engine and the rest of the rockets remains a constant. The kinetic energy of both is increased, a conversion of potential chemical energy of the fuel into heat and kinetic energy.