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# Inelastic collisions

In an inelastic collision, some of the kinetic energy is converted to other forms of energy. This energy can take the form of heat (thermal energy), sound or deformation of the structure of one of the objects.

Most real collisions are inelastic. The degree to which energy is converted does, however, vary widely.

While some kinetic energy is converted to other forms of energy, total energy is conserved.

The principle of conservation of momentum is maintained: $$m_1\vecphy{u}_1+m_2\vecphy{u}_2= m_1\vecphy{v}_1+m_2\vecphy{v}_2$$

In a perfectly inelastic collision, the two objects stick together after the collision.

Here, the principle of conservation of momentum takes the form: $$m_1\vecphy{u}_1+m_2\vecphy{u}_2=(m_1+m_2) \vecphy{v}$$ $\vecphy{v}$ is the final velocity of the new body.

A car crash is an example of an inelastic collision, as a large amount of kinetic energy is converted into the deformation of material.

Balls for squash (a racquet sport) are not very elastic. They convert a lot of kinetic energy into heat following collision with the wall and get quite hot during intense play.