(Intro)

We've been out looking for rocks to add to our rock collection, and, as you can see, Squeaks and I have found a ton of awesome rocks. We've just been putting them in a box, and we're ready to take them back to the fort so we can learn more about them. But, it looks like we might have collected a few too many. This box is really heavy, too heavy to carry. So, I wonder if we can pull the box back to the fort. Squeaks, do you want to give it a try? [Squeaking] Rats! Oh, sorry Squeaks, I mean, oh, man. That was a really good try, but we're going to have to think of something else.

If you've spent some time with us recently, you probably know that we can use simple machines to help us do work. In the past, we've used levers, ramps, and pulleys to help us move big heavy things, but none of those are quite the right machine for this problem. However, there's another simple machine that I think will do the trick. This simple machine is called a wheel and an axle. You already know what a wheel is, and an axle is the bar that goes into the middle of a wheel. In order for a wheel to work, it has to spin, and a wheel spins on an axle.

I bet you can think of lots of things that use wheels and axles, like cars and trucks, bicycles, roller-skates, roller-blades, and our wagon. Of course! We can put the box in our wagon, and then pull it back to the fort. Great idea, as usual. Thanks Squeaks. Our wagon has two axles and two wheels on each axle. So, we'll just put the box inside the wagon. OK, Squeaks, pull on the handle, and the box is on the move. We solved the problem!

But, how do wheels and axles help us to do work? It all comes down to how much force we need to move the box. We've talked about forces before, they're the pushes and pulls things put on each other. In this case, the force we're concerned with is the one we use to pull on the box. When the box was on the ground, Squeaks tried to put a big force on the box to pull it, but, even though he pulled really hard, he could only move it a little bit. But, when the box was in the wagon, Squeaks was able to pull it all by himself easily. So, it took less force to move the box, and that's what this simple machine does. A wheel and axle changes how much force we need to move something. Instead of a big push or pull, we can use a much smaller one, and smaller pushes and pulls means less work for us.

Because it takes less force to move heavy things, wheels and axles make it easier to move something a long way. That's why they are a part of so many things that help us stay on the go, and that's why you'll see wheels and axles on buses, scooters, wheelchairs, and [Squeaking] even robot rats. But, Squeaks is one robot rat that's earned a break. Hop in, Squeaks! I'll give you a ride back to the fort.

Thanks for joining us! If you have questions for us about machines or forces or anything at all, just grab a grownup, and let us know in the comments below or send us an email to kids@thescishow.com and we'll see you next time.