Whats the difference between static friction and sliding friction?

Answer 1

The coefficient of friction changes when an object starts moving (kinetic) from what it is when it is just sitting around (static). Usually, friction doesn't grab as hard once you get moving.

Answer 2

Static friction refers to the force of friction when an object is standing still on a surface, while sliding (or kinetic) friction refers to the force of friction when an object is moving relative to the surface. In order to budge an object that is at rest, you must overcome static friction. In order to keep it in motion, you must overcome kinetic friction. The coefficient of kinetic friction is typically smaller than the coefficient of static friction. If an object is rolling without slipping, then it is static friction acting on it even though the object as a whole is moving, because it is not moving relative to the surface at the point of contact.

By all means, check out my reference, which happens to be the Wikipedia article that the first answerer cut and pasted.

Answer 3

Static friction

Static friction occurs when the two objects are not moving relative to each other (like a book on a desk). The coefficient of static friction is typically denoted as μs. The initial force to get an object moving is often dominated by static friction. The static friction is in most cases higher than the kinetic friction.

Kinetic friction (of which "sliding" friction is one type)

Kinetic (or dynamic) friction occurs when two objects are moving relative to each other and rub together (like a sled on the ground). The coefficient of kinetic friction is typically denoted as μk, and is usually less than the coefficient of static friction. From the mathematical point of view, however, the difference between static and kinetic friction is of minor importance: Let us have a coefficient of friction which depends on the sliding velocity and is such that its value at 0 (the static friction μs ) is the limit of the kinetic friction μk for the velocity tending to zero. Then a solution of the contact problem with such Coulomb friction solves also the problem with the original μk and any static friction greater than that limit.

Since friction is exerted in a direction that opposes movement, kinetic friction usually does negative work, typically slowing something down. There are exceptions however, if the surface itself is under acceleration. One can see this by placing a heavy box on a rug, then pulling on the rug quickly. In this case, the box slides backwards relative to the rug, but moves forward relative to the floor. Thus, the kinetic friction between the box and rug accelerates the box in the same direction that the box moves, doing positive work.

Examples of kinetic friction:

Sliding friction is when two objects are rubbing against each other. Putting a book flat on a desk and moving it around is an example of sliding friction