There are some moments when you think that Don Pettit has lost his damn mind, in the coolest way possible. One of those moments is in this video, in which he turns himself into a floating disembodied head. And he does it, using just some water and the International Space Station.
There is plenty of physics to be found in this video. First there's the fact that the water droplet, which looks to be the width of a human palm, can hold together in the first place. Each of the water molecules coheres to each of the other molecules. This cohesion of the molecules is the reason why water molecules stay together as a liquid here on Earth. Of course, they only do that in certain numbers if they have a little support — say in a glass or a pitcher. Tip the pitcher, and a little water goes over the edge.
The drops that fall from the pitcher, provided it is on Earth, are small, because on Earth gravity is pulling down on them. Just as a sheet of ultra-fine tissue paper will eventually tear under its own weight if you spool it out long enough, a drop of water can only reach a certain weight, before it tears itself free from a larger source. In an environment like the International Space Station, where there is no effective gravity, there is no force tearing drops away from the whole and the cohesion of the water molecules can form drops much much bigger than we see on Earth. The principle is demonstrated again near the end, when a squirt of water causes the entire sphere to form a bubble with walls so thick that they would fall apart on Earth — but the bubble can be sustained in space.
Then there are the puffs of air that he squirts at the water molecule. This will set off two sets of ripples. Some ripples will go through the main body of the water. Some will travel over the surface of the water. The combination of inner and outer waves will go into a different pattern each time.
But the stand-out here is the accompanying talk. Astronaut Don Pettit talks how he's going to use the water to make tea, so he can drink his own experiment. He puts his hand behind the drop to show that the optics are the same in space. He then puts a black curtain behind it, and, at 3:40, hangs upside down behind the water drop, so he can make himself into a disembodied head. It's that moment that you realize you really want to get a drink with this man.
Best quote: "I'm going to give it another puff, just because I'm in space and I can."
You do it for all of us, Don.