You weigh less on the way down.

You weigh less on the way down.

Your mass is how much "stuff" you're made of. Your mass doesn't change. Your weight, as measured by a bathroom scale, is the force with which you push down on the scale. Weight = mass x g, where g is the acceleration due to gravity. If you are in an elevator, and it isn't moving, your weight is the force of gravity on you.  If the elevator is accelerating downwards, you push down on the scale with a force = mass x(g - a), where a is the acceleration of the elevator. Another way to think of this is that the scale, and the elevator, are scooting out of the way as you push down on them, so you can't push down as hard.