: Why is the outcome of two object colliding is determined by momentum 1 = momentum 2, instead of Kinetic energy 1 = kinetic energy 2?

Question

I think i’m missing something. When two object is colliding and no energy is lost why is the outcome determined by the total momentum formula? (m1v1 +m2v2 = m1v1′ + m2v2′)

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Why is it not total kinetic energy ? (¹/² m1.v1² + ¹/² m2.v2² = ¹/² m1.v1²’ + ¹/² m2.v2²’)

Why do we say momentum is conserved, instead of total energy is conserved?

In: 0

Answer 1

Kinetic energy is not necessarily conserved. In fact, it is rarely conserved. In most collisions, a ton of energy changes to other forms, such as heat.

Momentum, however, cannot change forms to something else and continues to exist as momentum.

So no matter what, momentum must be conserved, and *sometimes* kinetic energy can be conserved.