The Franck-Hertz experiment was a physics experiment that provided support for the Bohr model of the atom, a precursor to quantum mechanics.

The now-famous Franck-Hertz experiment elegantly supported Niels Bohr's model of the atom, with electrons orbiting the nucleus with specific, discrete energies.

The Franck-Hertz experiment confirmed Bohr's quantized model of the atom by demonstrating that atoms could indeed only absorb (and be excited by) specific amounts of energy (quanta).

It was during this time that Hertz and James Franck performed experiments on inelastic electron collisions in gases, known as the Franck-Hertz experiments, and for which they received the Nobel Prize in Physics in 1925.

Examples include traffic collisions, in which the effect of lost kinetic energy can be seen in the damage to the vehicles; electrons losing some of their energy to atoms (as in the Franck-Hertz experiment); and particle accelerators in which the kinetic energy is converted into mass in the form of new particles.