Chapter 7, Problem 7.1CYU

Check Your Understanding Can kinetic friction ever be a constant force for all paths?

To determine

Whether the kinetic friction can ever be a constant force for all the paths.

Explanation of Solution

Introduction:

Kinetic friction is defined as the force that can be generated between the moving surface. When a body is moving it experiences a force which is opposite to the direction of motion. The magnitude of this force depends on the coefficient of kinetic friction between the two similar material.

When a person is pushed backward by an another person, the first person starts sliding. Even though the two surfaces are sliding past each other, there is possibility of friction force between the surfaces.

The kinetic friction is given by,

$f_{\text{K}}={\mu }_{\text{K}}{f}_{\text{n}}$

Here, ${\mu }_{\text{K}}$ is the coefficient of friction, $f_{\text{K}}$ is the friction force. and $f_{\text{n}}$ is the normal reaction force.

Kinetic friction can never be constant as its direction keeps on changing so that it is always opposite to the motion of the body. It is only the magnitude of the kinetic friction that remains constant. Friction always depends on the vertical component of the force applied on the body. The magnitude of friction changes by varying the normal reaction force but since the normal reaction remains constant, the magnitude of friction remains constant as well.

Conclusion:

Therefore, the kinetic friction can never be constant due to the change in its direction. It is only the magnitude of the kinetic friction that remains constant.