# Boomerangs and Gyroscopes

## Introduction

Welcome to a day on which we'll be talking about gyroscopes and boomerangs. The reason we're going to talk about boomerangs is because I'm Australian! I grew up in Melbourne, which is about 11,0000 miles away. As we're recording it's a cold November
day in Cambridge, but in Melbourne it's a pleasant spring day of about 18 degrees. I think I know where I'd rather be! But I'm going to enjoy myself very much telling you about my favourite topic, which is gyroscopes and boomerangs.

When I was growing up in Australia I really knew nothing at all about boomerangs and nothing at all about gyroscopes. But I did have quite a fascination for moving toys, as lots of small boys do, and in particular I was rather fascinated by spinning objects. Now the cricket ball is a pretty important spinning object for Australians these days, and Shane Warne is a master spin bowler. I was
fascinated by the way that balls, when they are spinning and when they hit the ground, don't just bounce straight up but bounce sideways. So that's one aspect of spinning objects which I found quite fascinating.

But when I was at school my father showed me what could be called a "wobble" stone. It's made of wood, and is also called a "kelt" or a "rattleback". It has many names, and what's interesting about this object is that if I spin it clockwise, it wobbles about and comes back on itself. If I spin it anticlockwise however it's more or less happy to keep on spinning. So here's an object which won't
spin clockwise but will spin anticlockwise. Now I was really amazed by this, so I made one while I was at school.

It's a very carefully made, smooth-bottomed wooden object, but I've added a metal beam which can be turned around to change the weight distribution. I can spin it with the weight in one direction and it turns back twice - it doesn't like spinning in either direction. However if I spin it in the other direction, it wobbles about a different axis, comes back, wobbles faster, and comes back
again. If I change the weight distribution to the other direction, then everything is mirror image. If the weight is in the middle, it doesn't know what to do, whether to wobble around and come back, either direction is more or less alright, but it's very wobbly. I was fascinated by these.

You can buy these rattlebacks in shops, in the Science Museum or similar places, or you can make your own. If you get a telephone and persuade whoever owns it to let you take the back off it, the telephone has a curved surface like a rattleback. I've stuck a couple of 5p pieces in the telephone hand piece so that it's not balanced any more. If I then spin the telephone clockwise it wobbles
around and comes back. In fact it then turns round again. If I spin it anticlockwise it wobbles around about a different axis and doesn't really know what to do. You can really have fun and games with these sorts of things!

The thing that really fascinated me however was gyroscopes, and I really had a lot of fun collecting different types of gyroscopes and spinning tops in my travels. If there's a toyshop, I'll go into it and see if there is anything to be had. I found one for 50 cents in Melbourne a few Christmases ago. This is a spinning top which plays music [Fur Elise by Beethoven] and it's got
flashing lights as well. There are all sorts of spinning tops; I found another one in Melbourne which has a tooth belt, or pull belt, which you can pull to make it spin. It has flashing lights again, and a gyroscope inside the plastic case and you can really feel the gyroscopic effects. You can put it on the table and it stays up, spinning around, with the lights flashing. Well, it's all a bit of
a gimmick, the flashing lights, but it's good fun collecting these toys.

Today's talk is a serious look at some of these phenomena, the serious side of understanding how gyroscopes work and how various aspects of gyroscopic phenomena are of interest.

Next part of Hugh's talk