The ancient Greek, Aristotle had said that heavy objects fall much faster than light ones. For almost two thousand years everyone had just believed his idea.
But Galileo had a different idea.
He said that weight didn't matter. Any two objects would fall at the same speed.
(Stop watching when you get to the equation!)
Things actually do fall the way Galileo said, not the way Aristotle said.
But, they don't fall at exactly at the same speed. That's because some falling things are more affected by air resistance.
If they were dropped where there was no air, say on the moon, they would fall at the same speed:
We did an experiment to investigate air resistance.
It involved dropping different-sized paper helicopters and seeing which ones fell the fastest. Can you spot helicopters in any of these pictures?