Work EX 6

The work done by a force is zero if either:

• The force is perpendicular to the displacement, or;
• The displacement is zero.

(a) The force of static friction prevents sliding between two surfaces at rest with respect to each other. If the object does not move because of static friction then no work can be done. On the other hand, the force of static friction propels us to move forward as we walk and allows us to accelerate and move. Therefore in such cases the force of static friction does work in increasing our kinetic energy.

(b) The net force is always perpendicular to displacement in a uniform circular motion. Consequently, the work done by the net force (a centripetal force) is always zero.