The 3 Equations of Friction
Static friction (Fs): With static friction
there is no sliding, the friction force is exactly equal to the
Transition point: At the transition
point, the equation shown at right can calculate the highest possible
static friction and this is directly proportional to normal force, but
only at the transition point. Otherwise, static friction is determined
solely by the parallel force.
Dynamic friction (Fd): When sliding occurs,
the friction force remains constant. Typically dynamic friction is
lower than static but never higher. Dynamic or sliding friction is
influenced only by the normal force.
Friction Force vs. Parallel
Note: there are three distinctly
different equations. According to all three equations,
contact area has no influence on friction.