# Fundamental Force Question

1. Jul 31, 2009

### Stroodle

What's the minimum number of objects required for a force to be present?

I assume it's 2, because you'd need one object to be moved and the other to apply the force. Is this correct?

Thanks

2. Jul 31, 2009

### nickmai123

Umm... I take it you're enrolled your first physics class right now.

Anyways, when you talk about a physical system, take for example a person pushing a block, you don't count the person in the system itself. All that's there is just the block that's either moving at constant speed or undergoing uniform acceleration in the positive or negative direction. So I guess the answer to your question is 1...

3. Jul 31, 2009

### nickmai123

Do you know what a free body diagram is? If so, in that person pushing a block example, you just draw the block and a force vector coming out of it's center, pointed in the direction at which the force is applied.

4. Jul 31, 2009

### kuruman

You are correct. The number is 2. Newton's 3rd Law says that forces come in pairs, so if you have a single force acting on an object (as in a free body diagram), you can safely deduce that there is another object (somewhere in the Universe and outside your free body diagram) that experiences a force of equal magnitude but in the opposite direction.

Last edited: Aug 1, 2009
5. Jul 31, 2009

### Stroodle

Ahh. Awesome. Thanks for your help!