Why doesn't the Earth collide with the Sun?

porky

I am in AP Physics and we just got done with Centripetal force and Universal Gravitation. I was wondering since for the planets to stay in motion they need to have the same force as the object they are orbiting around. Since a bigger mass means a bigger force, how does the Earth stay in motion around the Sun.

Doc Al

I'm not sure I understand your point. Consider a planet in circular orbit about the Sun. The force needed to maintain the orbit equals mv²/r (the "centripetal" force), so the more massive the planet the greater the force needed. But gravity is proportional to mass, so it works out just right.

Molydood

also, technically the sun and earth are both revolving around one another, which may be a helpful way of seeing the situation.
or not.

gutti

I wouldn't look at it like that, that just leads to confusion in my opinion.

Newtons first law states an object will remain still or continue at a constant velocity in a straight line unless acted on by an unbalanced force.

Think of the earth as originally moving in a straight line, the gravitational force of the sun acted on it, but not enough to pull it straight into it, it pulled it around in a curve, and the velocity stays great enough that it will keep going round and round.

Think of a hammer throw, the object is getting pulled but not enough to go straight to the center, only enough to move in a circle.

A.T.

Because it is not in the way.

Doc Al

That's the best answer so far!