• All collisions are momentum conserving. But some collisions retain more KE than others.
• A (perfectly) elastic collision is one that retains 100% of its initial total KE.
• A perfectly inelastic collision is one that retains the minimum amount of KE.

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• Depicted above are just 5 possible outcomes of head-on collisions of two equal masses m with equal initial speed u.
• Notice that the total momentum (of zero) is conserved for all collisions.
• At the top is the (perfectly) elastic collision.
• At the bottom is the perfectly inelastic collision.

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• Depicted above are just 5 possible outcomes of head-on collisions of two equal masses m, one of them with initial speed of u, and the other initially at rest.
• Notice that the total momentum (of mu rightward) is conserved for all collisions.
• At the top is the (perfectly) elastic collision.
• At the bottom is the perfectly inelastic collision. (Losing all its initial KE is impossible because of momentum conservation)

• 03 Dynamics