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Conservation of energy in collisions
Intermediate
Kinetic energy is conserved only in elastic collisions.
Total energy is always conserved, but kinetic energy only in elastic collisions. Inelastic ones convert some into heat, sound or deformation.
Two equal clay balls collide at 2 m/s each and stick: all kinetic energy is lost.
Momentum is conserved in both types; kinetic energy isn't.
In more detail
In a collision, total energy is conserved, but kinetic energy may be converted to heat, sound or deformation. Elastic collisions conserve kinetic energy, while inelastic collisions do not.
Real-world uses
- Car crash analysis considers how much kinetic energy is absorbed by crumple zones.
- Billiard balls approximate elastic collisions, with little energy lost.
- Billiard balls in an ideal collision keep their kinetic energy, but a dropped clay ball loses most of its kinetic energy when it stops.
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Frequently asked questions
Is kinetic energy always conserved in collisions?
No. It is conserved only in elastic collisions.
Where does the lost kinetic energy go?
Into thermal energy, sound and deformation of the objects.
Are most collisions elastic?
Rarely. Most real collisions lose some kinetic energy to deformation, sound and heat.
Related topics in Work, Energy & Power
Mass–energy equivalence · Sources of energy · Renewable energy · Virial theorem · Principle of virtual work · Work–energy with variable mass