Difference between static and kinetic friction?

Answer 1

Static friction is the friction that acts between two objects which are not moving in relation to each other. For example, it is the force that prevents you a block from sliding down a ramp with a small incline.

Dynamic friction is the friction that acts between two objects which are moving in relation to each other. For example, it is the force that makes pushing a heavy box across the floor difficult.

Answer 2

Static friction describes the force needed to initially move a stationary object. There are tables of coefficients of static friction. The force needed to overcome static friction depends on the material making up the object, the surface the object rests on, the mass of the object and the acceleration of gravity. Static friction is generally higher than kinetic or sliding friction.

Kinetic friction (sliding friction) describes the force needed to keep an object moving along a surface. There are tables of coefficients of sliding friction available. It usually takes less force to keep an object moving than it does to initially get it moving from rest. This is because there is a small amount of attraction between the molecules of the object and the surface that must be broken to get it to move. Once moving, the two surfaces are not as tightly connected. You probably have noticed that it is harder to get a heavy object to move initially, but once you get it sliding across the floor it seems easier as long as it keeps moving.

Answer 3

Kinematics (statics) is the study of non-moving forces, ie the weight of my house on its foundation, the tension of a cable on a bridge. Dynamics is the study of moving forces, ie the wind moving a turbine, wake drag on a boat.

Answer 4

Static friction is the force resisting motion when the speed is zero. Dynamic friction is the force resisting motion when the speed is not zero.