Does density of a medium affect the conservation of momentum?

[JerryF]

Hi all,

If a body has a given initial momentum and then travels through a continuously less dense medium would it's velocity increase to conserve momentum?

Thanks
Jerry

 

[BvU]

No

 

[PeroK]

Hi all,

If a body has a given initial momentum and then travels through a continuously less dense medium would it's velocity increase to conserve momentum?

Thanks
Jerry

Momentum is typically not conserved for a body moving through a medium, as it will be subject to a resisting force. As it moves to a less dense medium it may decelerate less, but it cannot speed up without an external force to accelerate it.

 

[Nugatory]

If a body has a given initial momentum and then travels through a continuously less dense medium would it's velocity increase to conserve momentum?

No.
The resistance from the medium may become less as the medium comes less dense, but that resistance is always opposed to the direction of motion so always acts to slow the object and reduce its momentum.

Momentum is still conserved however. The medium exerts a force on the object to slow it, but by Newton's third law there is an equal and opposite force acting on the particles of the medium. At least some of these end up moving in the same direction that the object was moving, and these carry the momentum that the object lost.