State of motion of body change with force:

A body on contact with the surface is being pulled along it with the increasing force from zero. How does the state of motion of body change with force? Draw graph and illustrate.

Sol.: When the external force is applied on body and increases

gradually then initially static friction force acts on the body that is exactly equal to the applied force and the body will remain at rest. The graph is straight line for this range of force which is shown by OA on the graph. When the applied force reaches to the value at which body just begins moving, then the value of this friction force is called as limiting friction. Further any increase in force will cause the motion of the body and the friction in this case is dynamic friction. This dynamic friction remains constant with more increase in force.

Points to be Remembered

1. If applied force is not able to begin motion; frictional force will be equal to the applied force.

2. If applied force is able to initiate motion, and then applied force will be greater than frictional force.

3. The answer will not come in terms of normal reaction.

4. Assuming that the body is in limiting equilibrium.