# Do planets lose energy?

1. Aug 11, 2005

### Nocturn888

Why do planets rotate around the sun? due to the gravitational field of the sun, which is obvious, but why do they not gradually crash into the sun, due to their motion and the loss of energy after a while ?

2. Aug 11, 2005

### KingOfTwilight

Planets don't lose energy. (Actually they absorb energy, that is, the radiation from the Sun.) Centripetal forces never do work. Can you find why that is?

Hint: W = F * s, find s. (If you know vectors then do $$\vec{F} \cdot \vec{s}$$.)

EDIT:

One more thing, you may find this useful.

Last edited: Aug 11, 2005
3. Aug 11, 2005

### Nocturn888

so planets get energy from the sun? why doesnt their orbit increase in size then...? i know that gravitation bends space (and time), and that lighter objects are caught in this dent and therefore they change their motion and circumnavigate the sun. i dont understand how it is that centripetal forces dont do work, is it because they would actually still be going in staright line, at a steady speed, if there would not be dent and hence are only affected in their direction the planet would move? im not making much sense i think-.- sorry

4. Aug 11, 2005

### Nocturn888

thanks, from the link you gave me its making more sense, so there is no friction and hence no loss in energy and without there being any energy used up there is also no work done....(there is obviously no air resistance in space)