Question

Briefly explain what changing the gravitational force will do to friction on level ground.  Why does this happen?  How will this change on a hill?

Answer 1

Solution:

Gravitational force is weight of the object placed on ground. The object pushes the ground downward by this amout of force and ground exerts same amount of force on the object in upward direction as normal reaction.

The kinetic friction is directly proportional to the normal force acting between the surface of object which is in contact with the ground. Hence, on changing gravitational force the normal reaction force will change and thus the frictional force will get change.

Increase in gravitational force will increase the frictional force and decrease in gravitational force will decrease the friction force.

Frictional force arises due to surface irregularities, the inrease in gravitational force of object will dig in much deeper into those irregularities of the ground surface, hence, result in increase in frictional force.

In case of hill, gravitational force has a component along the normal direction of the contact surface at that point. The gravitational force makes angle with the normal direction same as the angle of the hill with respect to the horizontal direction. Thus, on increasing gravitational force the component along he normal force will also increase, hence, the frictional force will increase.