Movement Amount (continued)

Conservation of Movement Amount

Like mechanical energy, the amount of movement is also maintained when there are no dissipative forces, ie the system is conservative, closed or mechanically isolated.

A system is conservative if:

So if the system is conservative we have:

Since the mass of a body, or even of a system, hardly varies, what changes is their speed.


A body of 4kg mass travels at a constant speed of 10m / s. Another 5kg mass body is launched at a constant speed of 20m / s towards the other block. When the two clash, they will be caught by a velcro at their ends. How fast will the united bodies be?