When two surface are polished, the friction coefficient between them decreases. But the friction coefficient increases and becomes very large if the surfaces are made highly smooth. Explain.

For most of the surfaces used in daily life, the frition coefficient is less than 1. Is it always necessary that the friction coefficient is less than 1?

How does the friction arise between the surfaces of two bodies in relative motion?

A sphere can roll on a surface inclined at an angle theta if the friction coefficient is more than (2)/(7) g sin theta . Suppose the friction coefficient is (1)/(7) g sin theta , and a sphere is released from rest on the incline,

In the section 3.7.3 (Banking of road) we have not included the friction exerted by the road on the car. Suppose the coefficient of static friction between the car tyre and the surface of the road is mu_s , calculate the minimum speed with which the car can take safe turn? When the car takes turn in the banked road, the following three forces act on the car. (1) The gravitational force mg acting downwards (2) The normal force N acting perpendicular to the surface of the road (3) The static frictional force f acting on the car along the surface.

A classroom demonstration of Newton's first law is as follows: A glass is covered with a plastic card and a coin is placed on the card. The card is given a quick strike and the coin falls in the glass. a.Should the friction coefficient between the card and the coin be small or large? b. Should the coin be light or heavy? c. Why does the experiment fail if the card is gently pushed?

What is the angle of friction between two surfaces in contact if the coefficient of friction is (1)/sqrt(3)