Gravity

This is NASA's space power facility near Cleveland, Ohio, and it is the world's biggest vacuum chamber. It's used to test spacecraft in the conditions of outer space, and it does that by pumping out the 30 tons of air in this chamber until they're about two grams left. And it's kind of good in an eccentric construction, which is part of its history. It was built in the 1960s as a nuclear test facility to test nuclear propulsion systems and that meant that they built it out of aluminium to make the radiation easier to deal with. Aluminium is not the best thing. The strongest material to build a vacuum chamber itself. So they built out a concrete skin, which is part of radiation shielding and parts and external pressure vessel. So this thing can take the force that's present on the outside when it's pumped out to the conditions of outer space. Galileo's experiment was simple. He took a heavy object and the light one. And dropped them at the same time to see which fell fastest. Now in this case, the feathers fell to the ground at a slower rate than the bowling ball because of air resistance. So in order to see the true nature of gravity, we have to remove the air. It takes three hours to pump out the 800,000 cubic feet of air from the chamber. We drop 2 mL in the last 30 minutes, but once it's complete, there's a near perfect vacuum inside. 61 O four manual, 10% open, station one, go for drop. PCB 31, pressure set point of 240 psi. We are go for drop. Ten. 9. 8. 7. 6. 5. Four. Cameras on. Two, one, release. Yeah. Exactly. Look at that. They came down exactly the same. Wow. Exactly. Rebecca the silent look. Exactly the same. Feathers don't move nothing. Look at that. That's just brilliant. Isaac Newton would say that the ball and the feather fall because there's a force pulling them down. Gravity. But Einstein imagined the scene very differently. The happiest thought of his life was this. The reason the bowling ball and the feather falls together is because they're not falling. They're standing still. There is no force acting on them at all. He reasoned that if he couldn't see the background, there'd been no way of knowing that the ball and the feathers were being accelerated towards the earth. So he concluded they weren't.