Let us imagine a car (or just a block) moving in uniform circular motion with radius $R$ with velocity $v$, on a flat surface. It is obvious that friction is the only force capable of providing the centripetal acceleration $\frac{mv^2}{R}$. However, I have the following doubts:
- Is this friction static or kinetic? I feel that as there is relative motion occurring between the road and the car, it should be kinetic. However, my book and common experience says that is static as if it would be kinetic we could only move at a particular $v$.
- What would be the direction of the frictional force? I understand that the car would have a tendency to skid outward, and friction would try to oppose it, thus having a centripetal component. But why doesn't it have a tangential component, as the velocity of the cycle is tangential and friction acts so to oppose relative motion, which I interpret as opposing the direction of change of motion?
- I suppose when driving a car in circular motion we will need to put on the accelerator, but I do not see why we would need to keep applying a force to move circularly?