(Intro)

Have you ever played on a backyard water slide? It's one of our favorite kinds of summertime fun. You just lay a piece of plastic on the lawn, spray some water on it from a hose or sprinkler, get a running start, and then, you can guess what happens next, you slip and you slide. It's so much fun, but, even when it comes to fun, we here at SciShow Kids love to ask our favorite question: Why? So, let's stop to think about why this little bit of summer fun is possible.

First, let's think about all of the things that you need to make a water slide work. You need a long piece of plastic, and you need water, and then you need, well, you. So, somehow the plastic, water, and you work together to create slipperiness. How do they do that? Well for one thing, you can only tell if something is slippery or not if you're touching it, right? For example, a wet bar of soap can only slip out of your hand if you pick it up, and, in the same way, a water slide will only work if you jump onto it. So, slipperiness happens when two things touch, and when two things touch, they rub against each other. Sometimes, those things will slide around against one other, like the wet bar of soap against your hand or your body on the water slide. But, other times they don't.

Sometimes two things that are touching actually keep each other from sliding. Can you think of some things that aren't slippery? Well, Squeaks can drive up his ramp without sliding back down, and I can sit on my chair without falling out. What makes these things not slippery? It's called friction. Friction is a force between two surfaces that are trying to slide against each other. The more friction there is, the harder it is to get those two surfaces to move across each other. Take a book and push it across a tabletop. It's not hard to move is it? What if you took that same book outside, and pushed it on the sidewalk? Would it move as easily? Probably not. That's because the sidewalk is rougher than the tabletop, and that rough surface creates more friction when the book moves across it. So, how much friction there is between two things depends on what kinds of surfaces they have. Here's another example, think about when you're just walking around. Normally, you're not slipping and sliding all over the place when you walk down the street. That's because there's lots of friction between the bottoms of your shoes, and the sidewalk. That friction keeps you from sliding, but have you ever stepped on a patch of ice? It can be really slippery. That's because the ice is super smooth, so it creates less friction than the regular, dry pavement does.

So, what does all of this tell us? It tells us that things are more slippery when there's less friction. Let's see if that helps us understand how our backyard water slide works. What do you think would happen if you tried to go down the slide without any water? I don't think you'd be able to slide at all. And, what do you think would happen if we had water on the grass, but no plastic? I don't think you'd be slipping either.

The plastic slide gives you a smoother surface to play on than the grass. So, that help makes it more slippery, but you wouldn't get very far if you tried to slide just by throwing yourself on the plastic. So, the secret here must be the water. The water makes it so there's very little friction. The water comes between the two surfaces that are touching, that is between the plastic and you, to make a slippery layer that let's you go shooting down the slide.

Do you want to see some friction in action in other places? You can do experiments right at home if you're careful. You probably noticed that you can walk around on smooth floors, like ones made of wood or tile, in your sneakers and not slip, but if you're only wearing socks, you can slide across the floor. Why do you think that is? And, try pushing the book across the table again, but using different surfaces. Does it make a difference if you try to push the book across, say, a bath towel? What if you tried to slide it across a metal baking sheet?

Keep experimenting, and let us know what you discover. And, thanks for joining us! If you have any question about water slides or bikes or flowers or anything at all, just grab a grown up and let us know in the comments below. Or, send us an email to kids@thescishow.com, and we'll see you next time.