# Watch a Physicist Risk His Life to Prove a Law

When a figure skater spins, she can increase her speed by drawing her arms or legs in closer to her body because momentum is conserved. At least that’s the law the physicist above was trying to prove when he decided to drop himself 45 feet without a safety net.

In the video above, a physicist puts himself in free-fall to prove a point. Angular momentum, like energy, is a physical quantity that is conserved. It’s a product of rotational inertia, or a rotating object’s resistance to rotation, and velocity. When a figure skater draws in her arms to spin faster, she is decreasing her rotational inertia — it is harder to rotate something the further it is away from the rotational point. Since inertia and velocity are linked proportionally with momentum, if inertia goes down then velocity has to go up.

This increase in angular velocity is what the physicist was banking on. When the weight is dropped, it starts to spin. As he falls, his weight pulls the rope, in effect shortening the radius of that spin, like a skater pulling in her arms. Therefore the weight has to spin faster and faster around the poll, where at some point before he hits the ground the rope gets tangled enough for friction to save him.

And for any doubters out there, he also has the uncut version of the demonstration:

I’m sure of two things. First, even though I know the physics is sound, I wouldn’t try this without a backup plan. You know, like anything at all to stop your fall. Second, any teacher to try this for her physics students gets Teacher of the Year. Period.

IMAGES: NRK Viten