Ładowanie

The physics of skydiving

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[MUSIC PLAYING] The MIT Skydiving Club just jumped out of an airplane. It might seem like a wild adrenalin rush, but actually, there's a lot more to skydiving than just jumping out of a plane and pulling a ripcord. Skydivers can control their falls. They can sit, track, flip, fly head-down, make crazy hybrids, and even fly over to each other to dock. When you're just falling a few feet, there's not much you can do on the way down. So how is falling thousands of feet through the sky any different? You learn in school that things accelerate towards the ground because of gravity. But when things like skydivers fall for thousands of feet, another force becomes important. Drag. Gravity pulls skydivers toward the Earth. But as we fall, tiny air molecules bump into us. Each tiny bump causes a little bit of force against our bodies. The hit from one air molecule may not seem like a lot. But when you add all those tiny forces up, you get a big force called drag, which pushes up opposite to gravity. You can feel drag when you stick your hand out of a moving car window. When the jumpers first leave the plane, there's not much drag acting against gravity, so they accelerate towards the Earth. As skydivers fall and speed up, the drag force grows, and the skydivers feel the force of more and more air molecules. But with this comes control. And by positioning our bodies, we can stop flipping by pushing against the air. So what if Banks and I want to jump together? Can we fall at the same speed? Swati has a lot less surface area than me, so you'd think that she'd fall faster. But actually, she's so much lighter than me that she has a tendency to fall slower. But by reducing how much surface area is exposed to the air molecules, I can reduce drag and keep up with Banks. Drag can be used for more than just speeding up or slowing down. With your arms at the side and legs out generates extra airflow at your feet, which pushes your body in the direction it's facing. This is called tracking. To really use drag, air needs to push you hard enough, which can only happen if you're going fast enough. And that's why you can't track when you jump off of a high dive at a swimming pool. Skydivers can also do things like turn in place to create formations with each other. Other positions, like sitting, standing, and head-down, change the surface area as the jumper is exposed to the wind. Since fewer air molecules hit their bodies in these positions, skydivers can reach speeds up to 200 miles an hour. Skydivers would prefer, though, to not hit the ground at 200 miles an hour. Because they can't change the pull of gravity, they need to have as much drag as possible. So they open a parachute. The large surface area of the parachute helps us to slow down so we can land safely. Skydiving may seem like it defies the laws of physics. But in the end, it's just playing with the wind. [MUSIC PLAYING]