Science at Home

You Spin Me Right Round, Baby!

This month we decided to get dizzy while we explore the conservation of angular momentum. Wait, what?! This sounds super science-y and maybe even a little intimidating, but if you have ever played in an office chair then it’s actually something you’re already familiar with.

Angular momentum basically describes how much ‘oomph’ an object has when it is moving in a circle. To figure out an object’s angular momentum you need to know its mass, velocity and distance from the center of the circle. But knowing these values doesn’t actually tell us a lot; it’s when we start to make changes that things start to happen! This is because angular momentum is conserved: doesn’t like to change. This means that when you change one thing, like the distance the mass is from the center of the circle, something else will change so that the total angular momentum stays the same.

Okay, this can be challenging to understand without seeing this effect in action, so lets get on with the experiment! Here is what you will need:

  • A spinning office chair
  • 2 objects about 5 pounds in weight
  • Someone to spin you!

Lets spin!

  1. Sit in the chair and hold the weights, one in each hand, with your arms out straight
  2. Have your friend spin you round in the chair as fast as you’re comfortable with
  3. Once they let go, bring your hands in close to your chest
  4. Stand up carefully and try not to fall over from dizziness!

So what did you observe? What happened when you pulled your arms in close to your chest? Did you spin any faster? This is what should have happened!

As you pull your arms in, you changed the distance of the mass from the center of the circle: you made it smaller. Because angular momentum doesn’t like to change, one of the other factors must also change to counteract the change in distance. In this case, we saw an increase in velocity as you spin faster.

Try some other variations! What happens if you start with your arms in and you put them out as you spin? Or if you just put one arm out? What about both your legs instead? Just make sure you don’t get too dizzy enjoying all this science! And next time someone catches you spinning in a chair, you can explain to them that you’re just conducting a science experiment – honest!


Developed by Hannah Weiss and Koren Smith