What is frictional force?

static frictional force is self - controlled . Explain it .

A process against frictional force cannot be ________. [Fill in the blank]

What is force?

A body of mass 0.3 kg is taken up an inclined plane of length 10 m and height 5 m and then allowed to slide down to the bottom again. Coefficient of friction between the body and the plane is 0.15. What is the Work done against the frictional force over the round trip?

A car of mass 1500 kg is moving with a speed of 12.5 m cdot s^(-1) on a circular path of radius 20 m on a level road. What should be the frictional force between the car and the road so that the car does not slip? What should be the value of the coefficient of friction this force?

Gravitational force is a conservative force, but frictional force is non-conservative Why ?

What is friction? What is the origin of friction?