# Friction in a wheel for O levels

1. Jun 9, 2012

### sgstudent

Hi physicsforums, I know I have posted this before but i want to consolidate whatever I have learnt from the amazing tiny Tim into a single post to conform the simplified concepts. Thanks!
These are derived from here:
In particular, the friction from the road on the driving or braking wheels of a car is in the same direction as the acceleration or braking, but the friction on the non-driving or non-braking wheels of a car is in the opposite direction.

1)Friction of the driving wheel (wheel that is directly turned by the engines) is forward. Hence, if I'm sitting on a longboard and i start to turn the wheels, then that friction is forward. Thus pushing me forward.
1a) friction if the non-driving wheel (wheel that is just being pulled along by driving wheels) is backwards. Hence, in the same example in 1), the wheels that I'm not directly turning is backwards.
2)friction of the braking wheel (wheel that is directly being braked upon by clamps) is backwards. Hence, if I'm sitting on a moving longboard, and I suddenly press against my front wheels then the friction of those wheels are backwards.
2a)friction of the non-braking wheels (wheel that is not directly pressed upon when the braking wheels are presses upon) is forward. Hence, in the same example in 2), the wheels that is jot directly pressed upon has a forward friction.

As long as you don't directly push the wheels, your friction's direction is opposite to the motion (acceleration) of the body. So if I push the longboard without turning any of the wheels directly, the friction acting on all four wheels is backwards. But if I were to suddenly jump on the board and press on the front wheels to get a backwards friction, will my back wheels now have a forward friction? In accordance to the examples I gave?

Thanks for the help!