[ Intro ].

Squeaks and I are getting ready to visit the fair! There’s one around here every year, and there are all kinds of things to do — you can see lots of farm animals, eat some delicious food, and of course, there are plenty of rides!

My favorite ride is the roller coaster. But Squeaks was just asking me — and I thought it was a really good question — how roller coasters work. Because they’re not at all like the cars we drive on the street!

Instead, roller coasters have cars that run on a track. And the way they work is the same reason they’re so much fun: because of forces. You can think of a force as a push or a pull on something.

That’s how you make things move, or speed up or slow down! For example, bikes start moving when we put forces on the pedals with our legs, which turn the wheels. And things like cars, planes, and trains work because of the forces made by their motors.

But roller coaster cars don’t have motors, so the force that starts them moving has to come from somewhere else. Most of the time, the force comes from a strong chain attached to the tracks. The ride starts when the chain pulls the roller coaster cars up to the top of a big hill.

But when the cars start to go over the top of the hill, the chain lets go, and the ride keeps moving anyway, usually all the way to the end! That’s because a different force takes over. one you might have heard about before! It’s the same force that make a ball fall back down when you throw it into the air. [Squeaks squeaks].

Yup, Squeaks! The force that takes over is gravity. Gravity pulls everything on Earth down toward the ground.

And it’s gravity that pulls the roller coaster cars down over the hill and along the track. And once those cars get moving downhill…they can keep going! Roller coaster cars that have just gone down a big hill are going so fast that they can get up to the top of the next hill.

If they /didn’t/ have enough speed, they wouldn’t make it over the top, and they would just slide back down to the bottom and get stuck there. The people who design and build roller coasters know just how fast the cars are going to go… and whether they will be able to get over the next hill. And if they find out that the cars don’t have enough speed, they change the design to make sure the cars will be able to get over the top.

Or, they sometimes add another chain in the track to pull them to the top of the hill. Then, once the cars get to the top of that second hill… …gravity takes over again, and pulls them down and to whatever bend or hill comes next! But even though roller coaster rides can be really fun, they don’t last forever.

And that’s because of another kind of force. This force is called friction, and it pulls on things that are moving, slowing them down. Have you ever tried to slide along the floor in your socks?

If the floor is made of carpet, your socks scrape along it so roughly that there’s a ton of friction, and you probably won’t slide at all. If it’s made of something a little more slippery, like wood, you might slide a little. But eventually you stop because there’s friction when your socks scrape along the floor, slowing you down.

The same thing happens with the roller coaster cars. The tracks are slippery enough that the cars can slide along them for a while. But friction is still pulling on the cars, slowing them down, and eventually they stop.

So you can use the science of forces to make some awesome rides. But all good things must come to an end! In the meantime, though, we still have a fair to explore!

Are you ready to do this, Squeaks? Let’s go! Thanks for joining us!

If you want to keep learning and having fun with Squeaks and me, hit the subscribe button, and don’t forget to check us out on the YouTube Kids app. We’ll see you next time, here at the Fort! [ Outro ].