# B Friction guiding a car around a curve

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1. Jul 28, 2017

friction is causes the circular motion in the car around a curve, and if we draw free body diagram we will see the friction force must be opposite the car motion so the force of friction not toward to the center of the curve ,so the force of friction must be not the centripetal force ,mustn't it?

2. Jul 28, 2017

### jbriggs444

Kinetic friction opposes the relative motion between two surfaces that are in contact and are slipping against each other.

The thing that is in contact with the road is the contact patch on the bottom of the car's tires. That contact patch is not (usually) slipping relative to the road. So you have static friction, not kinetic friction. Static friction provides whatever force is required to keep the surfaces from slipping (within the limits of the coefficient of static friction). The static frictional force will not necessarily oppose the motion of the car.

If you slam on the brakes, friction from road on tires will point rearward.
If you step on the gas, friction from road on tires will point forward.
If you steer right, friction from road on tires will point rightward.