Question

When a force of 15 newtons is applied to a stationary chair, it starts moving. What can you say about the frictional force between the chair and the floor of the room?

Answer 1

Kinetic friction since the object starts moving

Answer 2

Answer:

That the maximum static frictional force is 15 N

Explanation:

The static frictional force is the force of friction that acts on an object at rest on a surface, when the object is pushed by an external force. The static frictional force acts in the opposite direction to the external force, preventing the object to start moving unless the external force overcomes it.

Due to its nature, the magnitude of the static frictional force varies between zero (if no external force is applied) to a maximum value, defined as

$F_s = \mu mg$

where $\mu$ is the coefficient of static friction, m is the mass of the object and g is the acceleration due to gravity.

The object starts to move only when the magnitude of the external force becomes larger than the maximum value of the static frictional force. In this problem, this happens when the external force is 15 N, so we can say that the maximum value of the static frictional force is 15 N.