Question

Can anyone explain about friction

Answer 1

Friction is the force that opposes the motion of an object. ... To stop a moving object, a force must act in the opposite direction to the direction of motion. ... As the book slides cross the desk, a force of friction (f) acts in the opposite direction.and  the angle of a plane to the horizontal when a body placed on the plane will just start to slide. The tangent of the angle of friction is the coefficient of static friction is called angle of friction.

Answer 2

Friction is the influence or force that acts in the direction opposite to the movement of the body. This arises because of uneven surfaces on the two bodies in contact.  If we see the bodies using microscopes, we find them rough.  So the pointed edges sharply brush against those of the other surface. So there is friction.

Friction is of several types,  static, dynamic or kinetic or rolling friction.
To start moving a body at rest, needs to be given a force more than the static friction. The static friction is less than or equal to  μ m g..  More the weight more the friction.

where μ = coefficient of friction <= 1.

Friction helps us in holding things, not slipping on roads or floor. If there is no friction, then we can not live properly at all.

Friction causes heat , wear and tear in objects and causes some energy to be wasted.

We need to use  oils or lubricants to reduce the friction and its negative effects.