Transcript

[SIGHING]

HELEN:

So I may not be the best bicyclist in the whole world, but ever since I learned to ride, and probably when you learned to ride as well, we learnt that when we go around the corner on our bicycles, we have to lean into the corner so that we don't fall over. And that's all about balancing forces, something we do very naturally when riding our bikes. And this next practical is all about motion in a circle and learning about how we balance those forces and how those forces help us to maintain that motion in a circle.

So Tom and I are now back inside in the warm in the lab. And we've gathered together all the things we need to do the experiment about motion in a circle. First of all, we've got a jar of lentils, pasta, rice. Anything like that will do. Second, we've got some plastic cups. This one is a clear one. This one is a paper one. Either one is just as good. And what we need to do is we need to take the cup, and we need to make a small hole on either side of the cup.

Now, I happen to be using the point of a compass, but you could use scissors or actually a pencil. Either one will do. And what you need to do is thread some string through each side of the cup to make something like this, which Tom made earlier-- a piece of string with two knots on it that can hang equally from either side of the cup. And now what I'm going to do is I'm going to ask Tom to fill the cup as bravely as he feels like with some lentils from the jar. Can you do that, Tom?

TOM:

Thank you, Helen. Well, I'm going to take the jar of lentils. I'm going to place some of these into the cup. I think that should be enough.

HELEN:

OK, Tom. Why don't you go and give that cup a whirl around in a circle?

TOM:

I shall certainly try, Helen. Thank you.

HELEN:

Now, the important thing for Tom to do is not to spill any of the lentils. Let's see if it's possible.

[LAUGHTER]

Well done, Tom.

TOM:

Thank you, Helen.

[CLAPPING]

There we go, and not a single lentil lost.

HELEN:

Wow, Tom. That was amazing. But I'm really confused. At some points, the cup was clearly upside down. How did the lentils not all just fall out?

TOM:

And it's amazing when you look at that. The fact that the lentils don't fall out, the reason behind that is the forces are balanced. So as it's going round in circular motion, the forces are balanced so that the lentils stay in as it's going round in a circle, very similar to what happens in the International Space Station. Now, you need to look at the text now as we move again to talking about circular motion and the International Space Station, how it stays in orbit around the Earth.