Why is it easier to pull a block than to push it.

Expert Answers
justaguide eNotes educator| Certified Educator

A block that is being moved is placed on a surface. There is a resistive frictional force in the direction opposite to that in which force is applied on the block to move it. If the normal force between the block and the surface it is placed on is N, and the coefficient of friction between the two surfaces is `mu` , the frictional force is `mu*N` .

When a block is pushed, a force is applied to do the same. This force is in a downward direction. If the angle of the force with the horizontal is `theta` , it can be divided into a component perpendicular to the ground equal to `F*sin theta` and a component parallel to the ground equal to `F*cos theta` . The perpendicular component increases the normal force; which in turn increases the frictional force. The resistive force is increased to `(F*sin theta + N)*mu` . On the other hand when the same block is being pulled, the force applied is at an angle to the plane but now the perpendicular component `F*sin theta` is in an upward direction; this decreases the frictional force to `(N - F*sin theta)*mu` . In both the cases the component parallel to the plane that is actually moving the block remains the same. It is the difference in the resistive force in the two cases that makes it easier to pull a block than to push it.