Equilibrium

Alright, Philip. Whoever knocks over most cones buys ice cream. -Okay, let’s go!! -Woohoo! Ice cream for me. Nice. -But!? How did that happen?

You also touched all the cones, I saw that. -Yes, but all my cones were in stable equilibrium. -What do you mean? -What does Kim mean? To grasp this we should begin with looking at a block. Every object has a centre of gravity. This is a point where we imagine all its weight is centred. This block’s centre of gravity is right there!

And the block has a supporting base. The area that it rests upon. As long as the centre of gravity is above the supporting base, the object won’t fall over, but watch: We tilt the block and -- now the block falls over. Let’s go back to the cones again. If the cone stands like this ...

As in Kim’s course. The supporting area is large. If you just tilt it slightly, it won’t fall over. But if the cone is up-side-down … as in Philip’s course. The supporting base is small, and it only takes a slight nudge for the centre of gravity to go beyond the supporting base.

And the cone falls over. Kim knew that would happen. We call the different types of equilibrium stable and unstable respectively. But what about that cone that’s lying down? What kind of equilibrium is that?

Let's look closer look at the cones. See that the centres of gravity are marked? If we tilt this cone the centre of gravity moves upwards. So the equilibrium is stable. But if we tilt that cone, the centre of gravity moves down, and so its equilibrium is unstable.

And finally: What if you push the cone that is lying down? The centre of gravity stays at the same level. This is when we say that the equilibrium is neutral. - Oh, here’s a replay of the race! Watch! - When I knocked these cones they tilted slightly, but then they returned to their initial position. They were in stable equilibrium. - And I only had to nudge those to make them fall over.

Those cones were in unstable equilibrium. - So there are three types of equilibrium. Stable, unstable, and neutral equilibrium. - What do you think, Philip: Can we find more examples? There are things in equilibrium everywhere. - Hmm -- a lamp hanging on one wire. That must be -- stable equilibrium. Because when I push it, it returns to the initial position at once. - Nice!

But if I … hmmm … cut off a tree. I only have to touch it slightly to make it fall. The tree is in unstable equilibrium. - But are there any more examples of neutral equilibrium? - I know! I know! Seamus’ ‘Status Wheel’!! - I wish I’d thought of that! - It hangs on his cabin, to show if he’s in or out, or whatever..

It’s attached in the centre of gravity so if Seamus turns it, it neither turns back nor keeps turning! It’s absolutely brilliant! - Yes. -- It’s in neutral equilibrium. - And there we have the three kinds of equilibrium. Stable, unstable and neutral. - But wasn’t there something else that we agreed upon? - Yeah, yeah ... I know.