What does kinetic friction mean?
First some vocabulary to understand, static = not moving and kinetic = moving (for the purpose of this explanation). There are microscopic ridges on all materials, when two materials are touching and not moving these ridges interlock to a degree. When you try and move these surfaces relative to each other it is harder to get them moving because you have to force these little ridges apart. A representation of this is called the coefficient of static friction. Once the surfaces are moving it is easier to keep them moving, and a similar representation of how hard it is to move these surfaces is called the coefficient of kinetic friction. Static friction is always larger than kinetic friction.
