The point particle is an idealized object where rotational and vibrational motion is ignored. Nevertheless, in many cases such degrees of freedom play a significant role. For example, the rotation and vibration of a molecule is an important “reservoir” of its internal energy. The excitation of these types of motion can occur during the collision process. Taking into account this effect, the collisions can no longer be considered as perfectly elastic but actually are inelastic. Some models for inelastic collisions have already been discussed and compared to experimental results. Here we present a mechanical system wherein we describe the vibrations upon impact in perhaps the simplest way possible; also we provide a qualitative explanation of the collision of a mono-atomic molecule with a nonrigid diatomic molecule.

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