# Braking distance and friction

1. Apr 17, 2014

### eddywalrus

I was taught that in conditions where there is less friction, such as on icy or wet roads, the braking distance of a car, is less than if the car was travelling in conditions with more friction, such as when the road is rocky or sandy.

Although it makes sense intuitively, I recalled that friction opposes motion and not acceleration. So, for example, when a car travels to the right, and the driver applies the brakes, the car will still travel to the right, but just decelerate until it stops completely. Since friction opposes movement, and the car is still moving to the right when braking, then the direction of the friction force is to the left -- so shouldn't a larger friction force decrease the braking distance?

2. Apr 17, 2014

### A.T.

There could be some confusion about sliding friction vs. rolling resistance here.

3. Apr 17, 2014

### eddywalrus

I'm not very knowledgeable when it comes to physics -- could you explain the distinction between the two for me? Thanks.

4. Apr 17, 2014

### sophiecentaur

I don't know if you really meant this but the braking distance in ice is Greater than with more friction.

5. Apr 17, 2014

### UltrafastPED

This is most certainly wrong, or wrongly stated.

And the rules for driving vary with the type of road surface; you drive quite differently on gravel than you would on pavement.