One of the hardest things to get your head around when you are a kid (or even now as an adult I will admit) is that the time it takes objects to fall to the ground is the same even if they have different masses. It's just doesn't make sense that a lighter object falls at the same speed as a heavier one. After all the heavier one pulls on your hand more and your instinct tells you it is going to fall more quickly.

Well here is some excellent footage from the Apollo space mission where a hammer and a feather fall at the same rate toward the moon. The lack of atmosphere removes the effect of drag on the feather. It really does look fake... but it isn't.

Of course wikipedia has some excellent information on our long lost scientific friend including information on how he showed this to be true on earth.