NewsScience Sundays

Actions

Science Sundays: The Science of Spinning

Posted at 6:00 AM, May 15, 2022
and last updated 2022-05-15 09:00:21-04

BAKERSFIELD, Calif. (KERO) — If you've ever found yourself in an office chair you know it can be tough to resist the urge to spin around! In this edition of Science Sunday we'll give you an excuse to spin around in your chair and, in addition to making you a bit dizzy, teach you a little more about the science behind spinning.

Items needed:

  • An office chair
  • Two small dumbbells or other light weights

Procedure:

Sit in the chair holding a weight in each arm with your arms extended and spin. As you're spinning, pull your arms in toward your body and note the change!

How it works:

As you pull your arms in you'll notice you start spinning faster! This is due to something called conservation of angular momentum. Conservation of angular momentum is a little bit tricky to define. Essentially it says that something that's spinning wants to stay spinning, with the same amount of spin. The easiest way to understand it is with a bit of math!

The formula for conservation of angular momentum is M x V x R, where M is mass, or how heavy something is, V is velocity, or how fast something is spinning, and R is the radius, which is how far something is from the point it's spinning around. To say that angular momentum is conserved is to say that the value of angular momentum doesn't change unless it's acted upon by an outside force.

Let's use an easy example and say each of those values is set to 2.

So (M x V x R) is (2 x 2 x 2) = 8.

Now, let's reduce the radius to 1. So if nothing else changes we have (2 x 2 x 1) = 4

That can't be right though, because angular momentum is conserved and can't change, so it has to equal 8. That means one of the other numbers, either the mass or the velocity has to change, and since the object can't get heavier, the velocity has to increase!

So our velocity doubles to 4, making the equation (2 x 4 x 1) = 8

In our demonstration, we reduce the radius by bringing our arms closer to our body, and as result our velocity, or how fast we're spinning, gets faster!

Real-world applications:

Athletes take advantage of the conservation of angular momentum all the time! This is especially true for Olympic sports like gymnastics, figure skating, and diving. Those athletes have to be able to quickly rotate their bodies and still manage to land safely on target. If you watch them, they almost always tuck their arms in to spin faster, and extend their arms to slow down and land.