### Conservation of Momentum

Like energy, momentum is *conserved* in physical systems. For
example, when two masses collide and recoil from each other, the total
momentum after the collision equals that before the collision. Since
the momentum is a three-dimensional vector in Euclidean space,
momentum conservation provides three simultaneous equations, in
general.^{B.10}

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Center of Mass

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Energy Conservation in the Mass-Spring System