Friction is good

Friday 30 December 2022

There have been a lot of this sort of video on the Internet this week and they high light something that is often a source of misconception.

Students learn that friction opposes motion so when they draw friction acting on a car they draw the arrow in the opposite direction to motion. But friction isn't always the bad guy, one way to convince students that it is forwards is to think about what would happen without friction. Cars would not be able to move forwards. Friction opposes the relative motion between two surfaces, the tyre rubber is moving towards the back of the car so the friction is forward.

I did a quick google search to see if most images showed friction opposing the direction of motion and lots did. The images aren't totally wrong but the show the friction exerted on the ground not on the car.