Applications of Kinematics and Dynamics B. Frictional Forces Key Concepts Frictional forces act to oppose motion.
Frictional forces negate the possibility of perpetual motion.
A force is needed to overcome static friction and to initiate motion. It takes more force to make an object move from rest than to keep it moving once it is in motion. For an object at rest, as more force is applied, more friction is encountered, until the limiting static frictional force has been attained. Additional force applied beyond that will initiate motion. Frictional forces that oppose the motion of moving objects are due to kinetic friction .