Science Centre: Gravity Defying Mug

Dave -  So, I've got a lovely little demo here.  I have a mug on a piece of string and on the other end of the piece of string is a little nut, of the metallic variety. So in fact, it's a M8 nut. The fact I know that from just looking at it, is slightly worrying. 

We're just going to run the string over the top of a mug and undo the knot in it otherwise, it's going to go horribly wrong....

Chris - So basically Dave, you've tied a mug, a china mug onto a lump of string and you got a little nut on the end of that 1-meter long bit of strong and a biro. You put the string over the biro.

Dave - The string is run over the biro. So, at the moment, I'm holding on to the nut. So, that's holding up the mug. And now, I'm going to let go of the nut.

Chris - It might go smash.

Dave - Okay, so 3, 2, 1...

Chris - Now, for the benefit of people that aren't actually able to see this because they're on the radio, Ginny, tell all.

Ginny - So, the mug looked like it was going to fall. Obviously, once Dave let go of the string, gravity was pulling it down and it fell quite a long way, but stopped about a foot from the floor. If we look closely, we can see what happened is that the nut has swung and wrapped itself around the biro several times and that's holding it in place. Why has that happened?

Dave - So, as the nut starts to fall, it starts to spin around the biro and as the string gets shorter and shorter, and shorter, it's a bit like climbing to the middle of a roundabout. As you climb to the middle of a roundabout, the roundabout gets faster and faster, and faster. So, the string spins around and round, faster and faster, and faster, until it's going fast enough to wrap around enough times that it doesn't fall out on the floor and smash.

Ginny - Probably not one to try with your mom's best china.