Question

Identify the correct sequence of events that take place when an external force acts on a block (at rest) kept on a rough surface.

• A. The block starts moving.
• B. Static friction starts acting on the block.
• C. Kinetic friction acts on the block.
• D. The block continues to be stationary.

Answer 1

When an external force acts on a block (at rest), to oppose this force, friction comes into play. However, the type of the frictional force that acts on the block depends on the motion of the body. The following would be the sequence of events that happen in this case.

• A. Static friction begins to act on the block opposing the external force acting on it.
• B. The block is still stationary as long as the static friction is equal to the external force.
• C. When the external force is greater than the static friction, the block starts to move.
• D. At this point, static friction disappears and kinetic friction comes into play (during the motion of the block).