: 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

For ideal, perfectly rigid objects it’s both, and that’s how we calculate their speeds after collision. Total energy is also always conserved. However, in real world scenarios some energy will be turned into heat by the collision while total momentum cannot go anywhere.