# HELP gravity?

1. Nov 28, 2005

### khizman

If two people - one weighing 10 stone and the other weighing 20 stone - both jump off a building who would hit the ground first?

I know they would land at the same time but why?

2. Nov 28, 2005

### Fermat

It all depends on the air resistence - if there is any.
If they jumped of a building on the moon, an airless environment, then they would both have the same acceleration and would hit the ground at the same time, regardless of their weights.

On the earth, where there is an atmosphere, then there would be air resistence, which would slow down the fall.

Air resistence would depend upon the profile, or outline shape of the falling bodies, as well as other factors. A grosser body would have a greater profile than a leaner body and so would have a greater amount of air resistence. The more resistence, the longer it would take to fall.

3. Nov 28, 2005

### Chi Meson

If air resistance is negligible (such as for a short jump) the acceleration due to gravity of all things is the same. This comes from comparing two formulas. One is the simple formula for calculating weight (force of gravity) near the earth's surface. The other formula is Newton's second law. Rearrange this second law formula to solve for acceleration.