[13-Forces 视频] 在光滑的地面怎么摩擦 | Friction

Why can you easily ski over smooth snow? And why are slides more fun when they're wet?

The force that determines how fast or slow an object slides across a surface is called friction.

Friction acts between two surfaces.

It pushes against the moving object. It slows it down, until it stops.

The amount of friction – or grip – depends on the materials of the two surfaces: the smoother the surface, the less friction; the rougher the surface, the more friction.

It also depends on how heavy the object is. The heavier the object, the more friction between it and the surface.

Cars can drive because of friction – resistance between the car's tyres and the road.

Friction helps your skateboard wheels grip the road, and you use friction again when you squeeze the brakes on your bike.

If there was no friction, walking and running would be impossible as we would slip and slide all over the place, like skating on ice.

You couldn’t hold a pencil without friction – or make a mark – or rub it out!

Without friction, everything would slip out of your hands, like a wet soap!

Friction also produces heat. When it’s cold outside, rubbing your hands together will warm them up.

Some things are built to reduce the effect of friction. Their surfaces are made to be more smooth, or lubricated with liquid, which reduces friction by pushing the two surfaces apart.

When things are wet, they become more slippery.

Some things are built to increase friction. Like putting grit on icy roads. Goal keepers often wear gloves with rough surfaces to help grip onto the ball.

How else could friction be useful?