How Does The Earth Spin?
[Music] If I, uh, apply a force to the globe, I can actually get it spinning in roughly the same way that the Earth spins. But it is tricky. There's very little friction on the bottom because of it being supported on this thin layer of water. You can see the more force I apply to it, the more it accelerates.
Ooh, so we're getting it speeding up here. When you push that, like, it's not too easy to get it going. Why is that? Friction, probably. So why is it not really easy to push? What is it about this giant sphere that makes it a challenge to push?
The weight, the resistance. We're gravity. Gravity, it's really heavy too, so I'm pretty sure the weight of it sitting down is making it tough too. You don't think its weight is supported by that water? Well, I know it's supported, but even though it's supported, moving it is still like—if the center of gravity is here, we still have to push the weight coming out from here, so it's pretty heavy.
I'm pretty sure most people will say if you just apply force to it, it starts moving. That's not really the point I want to make. The point I want to make is the more force you apply to it, the more it speeds up—more gets going faster and faster and faster. But it's got 2 and 1 half tons of inertia, so you can really feel that you have to push hard to accelerate it.
What do you feel when you push on it? It just moves. When you push something, it moves. Does it do something more than move? Spinning? Its rotation? Velocity? Speed?
There's some word you're looking for. There is a word I'm looking for. What do you feel? Is that hard? Uh, not really. It's easy. Easy? It's not going very fast though. It's not like hard to push, but it's sort of hard to get going fast.
It's too big to make it fast. Is it hard to make it fast? Yeah. Why is it hard to make it fast? Can we try? Yeah, let's try. Let's get it going really fast.
How is that rotating sphere so close-moving? How do you make it go faster? Um, we only need to push hard, hard, hard, and more harder than that. You put a force on an object, a net force, an unbalanced force, and it—come on, goes!
Go the least scientific! Whatever! It goes. You studied physics, right? Yeah, which means I'm probably looking a little bit like a fool here. It's easy to push, but like, if you try to go fast, then it just sort of stays the same speed. But could you bring it to a stop? Probably not. Definitely not. Can you give it a shot?
It's off the water. Well, other than cheating? Yeah! What do you think? Not going to happen, really? Come on, come on, come on! Put your back into it! You can do it!
I don't think it's going to work, but we can give it a shot. Kind of. What do you see? There, it stopped! But I—it's only stopped 'cause it's on like a very soft thing of water, pretty much, I'm pretty sure. So it's not going to stay stopped, or what?
[Music] Shouldn't, huh? All right, are you applying a force to this sphere here? Yes. What happens when you apply a force to the sphere? Then it changes like speed.
That's a pretty awesome observation you've just made! Yeah, do you know that? I guess so. We could generalize; we could say force causes change speed. Man, you were nailing this!
Can you give me a high five? Boom! What do you think physics is? Um, like how things work, I guess. And you want to know how things work? Yeah. How old are you? Eleven. You seem pretty smart for being eleven.
Okay, do people tell you that you're smart? No. Do you think you're smart? No, I think you're smart. Okay, you take my word for it? Okay, really? Yeah, I guess.