The gravitational force between the earth and you keeps you on the ground.

And that force is your weight.

The Renaissance scientist Galileo Galilei proved that this gravitational force causes objects, light or heavy, to have the same acceleration when they fall.

So does that mean that two people of different weights are equally fast?

Well, no.

And here's why: When you move through the air, you create drag-- a force that slows you down.

And the faster you go, the greater the drag.

When drag matches the gravitational force of your weight pulling you down the hill, you've hit your top speed.

To go faster, you can extend the wheel base so you can lie flat and reduce your drag, or you can add weight to the bike so there's more force pulling you down the hill to overcome the drag.

So, if you have two equally skilled riders, the one who's heavier should be faster.