centripetal-forceforcesfree-body-diagramfrictionnewtonian-mechanics
The velocity of a vehicle while taking circular turn is tangential to circular path. Friction opposes relative motion between ground and tyres. Then how does friction act radially inwards?
In other words, why does the car tend to go radially outwards although its velocity is tangential?
This is my attempt to illustrate what happens when the car wheel is turned:
Focus on the bit of the car tyre marked with a red spot, and the bit of the road marked with a green spot. If we could look at the contact patch between the tyre and the road we'd see something like the rectangle I've drawn on the left. When the wheel is straight the red spot on the tyre and the green spot on the road move together (I'm assuming the car is moving to the left so the ground is moving to the right).
but now suppose we turn the wheel to the left. The contact patch now looks like the rectangle on the right. Because the patch has been rotated relative to the road the red and green spots now don't move together, but instead the red spot on the tyre is scraped across the road surface. It's this lateral motion of the tyre surface across the road surface that causes the frictional force that turns the car.
Friction is in the opposite direction of motion.
When you spin your wheels, you are trying to push the road backwards. The reaction to that friction is to push your wheel forward.
When you turn, you are changing the angle the friction is acting. Instead of just trying to push the road backwards, it also tries to push it to the side opposite that you want to turn. The reaction from that creates a component of the force acting in the direction you want to turn, leading to the circular motion.
Best Answer
Tires/wheels are interesting objects. In the ideal case they allow zero restriction to motion in the plane of the wheel (rolling motion) and they prevent motion perpendicular to the plane of the wheel (sideways motion).
So even though the car is moving forward, the contact patch of the tire and the ground are not moving relative to each other. We presume that friction is zero when the car rolls straight ahead.
When the tire direction is shifted (by turning the steering wheel), a component of the vehicles velocity is now perpendicular to the tire plane. The tire attempts to resist this motion and a friction force appears. Because this force is on the front of the car, it both moves the car sideways and turns the car (and becomes a centripetal force).