Name some ways that friction can be and some ways it is harmful?

Friction is helpful:
- We use it to brake for cars
- We use it to fly planes
-We wouldn't be able to turn a door knob without friction ( Our hand would just slide off it)

Friction harmful:
-Our cars would get much better gas mileage without tire and air friction
- There would be no skinned knees if friction didn't exist (Like when your skating or football)
- We could do some pretty cool dance moves without friction
- Our shoes would last longer without friction