"Friction occurs when two bodies are in contact and forces are applied to one or both bodies. Frictional forces develop at the contacting surfaces that tend to inhibit the sliding of one body relative to the other. For example, it is friction between the tires and road that keeps a car from sliding off when it rounds a turn. This ability of a tire to maintain contact with the road is often referred to as traction." p10-1

COEFFICIENT
A NUMBER THAT IS USED TO DO CALCULATIONS, OFTEN TO CONVERT ONE KIND OF MEASURE TO ANOTHER.

COEFFICIENT OF STATIC FRICTION

DRY FRICTION

DYNAMIC FRICTION
THE FRICTION THAT ACTS WHEN TWO SURFACES MOVE PAST EACH OTHER WHILE IN CONTACT.

FORCE
A PUSH OR A PULL

FORCE

FRICTION
A FORCE OF ABRASION OR FLUID DRAG

NORMAL
IN MECHANICS, NORMAL OFTEN MEANS PERPENDICULAR OR AT RIGHT ANGLES TO A SURFACE OR A DIRECTION. NORMAL CAN ALSO MEAN NOMINAL OR AVERAGE.

NORMAL FORCE
A FORCE THAT IS PERPENDICULAR TO A SURFACE OR THE DIRECTION OF MOTION OF A SYSTEM.

STATIC FRICTION

STATIC FRICTION