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Forces and Motion

Momentum - Law of Conservation.

What is the Law of Conservation of Momentum?

The law of conservation of momentum states that
the total momentum of a closed system does not change.

This means that when two objects collide
the total momentum of the objects before the collision
is the same as
the total momentum of the objects after the collision.
Total momentum means
the momentum of object 1 plus the momentum of object 2.

Object 1 might not have the same momentum before and after
the collision
but the amount of momentum object 1 gains from the collision
is the same as the amount of momentum object 2 loses
so the total momentum
remains the same whether the collision is elastic or inelastic.

The total momentum is also the same before and after an explosion.


What does Closed System mean?

"Closed system" is used to mean that only the forces of
the two objects colliding affects the motion of the objects.
See Newton's third law of motion.
If another force (called an external force)
affects the motion of the objects
then the momentum is not conserved, it will change.

The term closed system has a different meaning in chemistry.

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