A wooden block lies on a horizontal table. Answer the following questions about the friction acting on the block.
a. (a) Define static friction and limiting friction.
b. (b) A horizontal force F is applied to the block and is increased slowly from zero. Describe qualitatively how the magnitude of the frictional force acting on the block varies with F until motion begins.
c. (c) If the block just starts sliding when F=F1 and the coefficient of kinetic friction is μk(<μs), explain what happens to the magnitude and direction of the frictional force immediately after the block begins to move.