Conservation of momentum with friction?

[raman911]

Homework Statement

We know that momentum is supposed to be conserved in this collision. We observe, however, that the pucks eventually come to a stop, at which point they have zero momentum. Give a solid explanation (using the law of conservation of momentum) for this apparent violation of the law of conservation of momentum.

 

[G01]

What causes a change in momentum?

 

[ogb p]

I can explain this apparent violation of the law of conservation of momentum by taking into account the presence of friction. When two objects collide, their momenta are transferred to each other, resulting in a change in their velocities. However, in the presence of friction, there is an external force acting on the objects that opposes their motion. This force causes the objects to slow down and eventually come to a stop, resulting in both objects having zero momentum.

According to the law of conservation of momentum, the total momentum of a closed system remains constant. In this case, the closed system includes both pucks and the surface they are sliding on. While the pucks may lose momentum due to friction, the surface gains an equal amount of momentum in the opposite direction. Therefore, the total momentum of the system remains constant, satisfying the law of conservation of momentum.

It is important to note that in real-world situations, it is rare for a system to be completely closed and not experience any external forces. In most cases, there will be factors such as friction, air resistance, and other external forces that can affect the conservation of momentum. As scientists, we must take these factors into account when studying collisions and other physical phenomena.

In conclusion, the apparent violation of the law of conservation of momentum in the case of pucks coming to a stop can be explained by the presence of friction and other external forces. The law of conservation of momentum still holds true, as the total momentum of the system remains constant.