# Question on gravity?

1. Jul 20, 2010

### Jorge610

What I've been trying to figure out recently is: I understand that all objects fall at the same rate but don't understand how this makes sense given that things weigh different amounts. For instance, if I were to have a large person sit on my chest they would press much harder against me because of gravity than a small child, leading me to believe that the more massive adult is displaying more gravitational "force", but they fall at the same rate? Why?

2. Jul 20, 2010

### DaveC426913

Because a more massive object takes more to accelerate it to the same speed as a less massive object.

The extra pull is exactly balanced by the extra inertia to not move.

Another way to look at it. Forget about gravity for a moment. Turn the experiment on its side. If you attached ropes to a small obejct and to a large object, and then pulled on them, would you expect the more massive object to leap towards you faster than the less massive object?

3. Jul 21, 2010

### Jcskehan

I think it's more like this

(GmM)/(r*r) = ma

cancel out the little m (say its the mas of the falling object)
and we have the gravitational constant times the mass of the earth, divided by the distance from its center, squared, as the acceleration of gravity. on most of earth, thats 9.81. :)

4. Jul 21, 2010

### ZapperZ

Staff Emeritus

Dave has given you a very good "intuitive" reason why this occurs. While a larger mass may have a larger weight, it also has a larger inertia. So the greater force it has just about cancels the larger force one needs to move a heavier object by the same rate.

Zz.