The Equivalence Principle enunciated by Albert Einstein says that any two objects in a uniform gravity field will fall at the same rate if dropped from a height. Of course, if we drop a feather and a bowling ball, that is not what we see and we explain that by saying it is because the air resistance slows down the feather much more than it does the bowling ball. But if you could drop the two items in a vacuum, they should fall at the same rate.
The catch is that getting a vacuum in a large enough volume is not easy. Astronaut David Scott, when on the moon in 1971 as part of the Apollo 15 mission, ran a rough experiment using a hammer and a feather and showed that they both hit the ground at approximately the same time.
But here is a more spectacular demonstration using a bowling ball and feathers done on Earth with more precision and using high-speed cameras to capture the action. To do that, they used a facility near Cleveland consisting of a massive chamber that is capable of being evacuated to something approximating outer space, no mean feat when you consider the enormous pressure that the surrounding air exerts on a high-vacuum chamber. The resulting video is quite beautiful. What is interesting is how, even though we have so much confidence in the Equivalence Principle, demonstrating it still causes such surprise and pleasure.