Suppose you attempt to pick up a very heavy object. Before you tried to pick it up, the object was sitting still its momentum was not changing. You pull very hard, but do not succeed in moving the object. Is this a violation of the momentum Principle? How can you be exerting a large force on the object without causing a change in its momentum? What does change when you apply this force?

In physics, momentum is one of the two most basic concepts. Momentum is a property that does not change unless force is applied to it. A force is produced by any change in momentum.

The rate of change of momentum of an object is equal to the net force acting on the object, which is given by,

$\frac{d\stackrel{\rightharpoonup }{p}}{dt}={\stackrel{\rightharpoonup }{F}}_{net}$

Here, is the momentum, and${\stackrel{\rightharpoonup }{F}}_{net}$ is the net force acting on the object.

The law of conservation of momentum is applicable only when the net external force is applied to the body. And here, the net force is zero So, the momentum is not violated. Even though by applying a large force on the object, the net force is zero.The net force is the summation of the force you apply and the normal force applied by the surface on the object So, the change in momentum is zero. This applied force causes the decrease in normal force which is the force exerted on the object by the surface.

Thus, the principle of momentum is not violated. But the applied force cause decrease in the normal force.