I have a few basic questions about conservation of linear momentum:
When the example of particle colliding in a 3D box are used to explain conservation of linear momentum, do we assume that the system is completely isolated? If so, then then total energy of the system must remain constant.
In my understanding, we assume that the system cannot transfer energy in ANY other form (such as sound, radiation) other than changes in kinetic energy. However, do we also assume that the system is not placed inside any potential fields (such as gravitational potential fields)? Therefore, unable to lose PE also?
Ultimately, these constraints on the system mean that the only energy transfer between the particles can be in the form of changes in kinetic energy.
Additionally, when we can use the assumption that the conservation of linear momentum applies to a system of interest? Should the system be arranged such that the only changes in energy are changes in KE? and changes in PE, sound energy etc. are negligible?