# Why static friction not kinetic in this problem?

Tags:
1. May 31, 2015

### Tahmeed

1. The problem statement, all variables and given/known data

The sports car ) is rounding a flat, unbanked curve with radius R . If the coefficient of static friction between tires and road is Us, what is the maximum speedat which the driver can take the curve without sliding?

why in this problem i am given Static fiction coefficient instead of kinetic???

2. May 31, 2015

### ehild

Because we do not want the car sliding out of the curved track. The piece of tyres in contact with the asphalt should not move relative to it.

3. May 31, 2015

### Tahmeed

can you clear?? i didn't get it.

4. May 31, 2015

### CWatters

Which direction is the friction acting?
Is the car moving in that direction?

5. May 31, 2015

### haruspex

Friction relates to surfaces in contact. The choice of static or kinetic friction is determined by whether there is relative motion between the two surfaces. The motion of the car is not important; what matters is whether the part of the tyre in contact with the road is moving relative to the road - i.e. skidding.