Since force is related to a change in momentum and not necessarily just to a change in velocity, what would be an example where only the mass of a body changes but not its velocity when subjected to a force?

Question

Since force is related to a change in momentum and not necessarily just to a change in velocity, what would be an example where only the mass of a body changes but not its velocity when subjected to a force?

In: Physics

Answer 1

Momentum is something that exists in mass. If you apply a force, it inherently *must* change an object’s velocity (however slightly) and does not change its mass.

To increase the momentum of an object, you must decrease the momentum of another object, as momentum is a conserved quantity. Note that momentum is a vector, and so a “decrease” could just as well mean an increase in the opposite direction. The force ‘moves’ momentum between the two objects.

The force could, instead, move mass between the two objects, but the scenario is a bit odd, since the new mass isn’t necessarily the same object but simply travels alongside the object.

For example, imagine a very fast aircraft flying over enemy territory. So fast that it keeps pace with bullets. The enemy fires upon the aircraft, but the bullets can only match speeds with it and will not damage it. The bullets are now traveling with the aircraft, and with some mid-flight gluing they could become a part of it. In this case, the force of firing the bullet is pumping mass to the object without changing its velocity.