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Overview
An inelastic collision is a collision where total momentum is conserved, but total kinetic energy is transformed into other forms such as heat, sound, deformation, vibration, or internal energy.
Momentum Is Still Conserved
If the system is isolated, total momentum is conserved in an inelastic collision even when kinetic energy changes form.
Kinetic Energy Is Not Conserved
In ordinary inelastic collisions, total kinetic energy after the collision is less than before the collision, but total energy is still conserved.
Perfectly Inelastic Collisions
A perfectly inelastic collision occurs when objects stick together after impact and move with a common final velocity.
Deformation, Heat, and Sound
Energy may go into bending, breaking, heating, compressing, vibrating, or producing sound.
Before and After Method
Inelastic collision problems often use a before-and-after momentum equation to solve for final velocity or momentum.
Examples
A lump of clay sticking to another object, a car crash, a football tackle, or a soft-object impact can be inelastic.
Common Mistakes
A common mistake is assuming kinetic energy is conserved because momentum is conserved. Another is saying energy is lost rather than transformed.
Applications
Inelastic collisions are important in crash safety, sports, materials testing, manufacturing, ballistics, and impact engineering.
Why This Matters in Physics
Inelastic collisions connect momentum conservation with real-world energy transformation.