# What does the law of conservation of momentum mean?

Mar 5, 2018

It means that in a collision (even an inelastic collision) total momentum after the collision is the same as total momentum before the collision.

#### Explanation:

Momentum before = momentum after
${m}_{1} \cdot {u}_{1} + {m}_{2} \cdot {u}_{2} = {m}_{1} \cdot {v}_{1} + {m}_{2} \cdot {v}_{2}$
where the u terms are initial velocity and the v terms are velocity after the collision.

If the 2 become stuck together, then ${v}_{1} = {v}_{2}$ so we can simplify the above formula to

${m}_{1} \cdot {u}_{1} + {m}_{2} \cdot {u}_{2} = \left({m}_{1} + {m}_{2}\right) \cdot v$

I hope this helps,
Steve