What if the mass of a system is not constant, like with a rocket? Most of the mass of a rocket when it's on the launch pad is fuel, but that gets burned and ejected through the rocket engine. So we have to use Newton's Second Law to not only the rocket alone but also to the rocket and its ejected combustion products all taken together, so the mass of the system doesn't change as the rocket accelerates... this makes solving the problem a LOT easier.

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Highlights for Momentum & Impulse

• Impulse is the amount of time a force is put on an object. How hard and how long something gets pushed or pulled.


• Ft = Impulse. Impulse affects the momentum of an object.


• Momentum is inertia in motion, how hard it is to get something to change directions or speed. Momentum = mv.


• Conservation of momentum; mv = mv. If something hits something else the momentum of the objects before the collision will equal the momentum of the objects after the collision.

Yay! You completed this section! Now it's time for you to solve physics problems on your own:

Download your Momentum Problem Set here.

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