(
Race cars move super fast and drive hundreds of miles in every single race. They’re made of a ton of moving parts that are constantly moving and rubbing against others while their tires are constantly moving against the ground. When things touch and move past each other, it creates a force called friction, and friction is important to how race cars move.
This Slip Sliding activity will explore friction from a different point of view.
Materials:
- Toy cars
- A cookie sheet
- Water
Process:
- Fill the cookie sheet with water and then put it in the freezer until the water has completely turned to ice.
- While your water is freezing, test out your Hot Wheels cars on a nice, smooth table or floor. Give them a good push. How do they move? Do they go straight? How do the wheels move? Test it out a few times, so you get a feel for how they move over a normal surface.
- Take the cookie sheet out of the freezer and spread a small amount of hot water on top of the ice. Make sure it’s just enough to melt the very top layer of ice and leave it nice and slippery.
- Put a Hot Wheels car at one end of the cookie sheet and give it a good push just like you did before on the normal surface. What happens to it as it tries to move across the slippery surface? How does it move? What do the wheels do? How is it different from what you observed before? Try it a few times to gather lots of observations.
What's going on?
Quickly rub your hands together. What happens? Do you feel them getting warmer? That’s friction in action.
Friction is a force that resists things moving against each other. This means that when two things, like a race car tire and the road, are touching, and at least one of them is moving, friction wants them to stop moving. If a race car driver took his foot off the gas pedal, the friction between the tires and the road (and even between the car and the air around it) would cause it to slow down and eventually stop. Often friction generates heat, like when you rubbed your hands together.
You might think that a race car wouldn’t want any friction between its tires and the track. Then it could go really fast, right? But ice is a slippery surface, which means it doesn’t have very much friction. What happened to your cars on the slippery ice? Too much friction makes it hard to move, and not enough means you’re slipping and sliding all over the place. If that happens when you’re going 200 miles an hour it could be very, very dangerous.
This is why the pit crews at a racetrack change out the tires on the cars so often during a race. Friction rubs the rubber off of tires until they are smooth. If they’re too smooth, the car becomes dangerous to drive, so the driver makes a pit stop to get some new tires put on. They also change the oil in the engine, which changes the friction in the engine. Unlike the tires, they want less friction in the moving parts of the engine. If there’s too much, the engine could get too hot and become damaged, which is also dangerous.
