Kinetic energy

Summary

The kinetic energy of a particle is half its mass times the square of its speed, the energy it has because it moves. In classical mechanics, the work of the net force on a particle equals the change of its kinetic energy. Together with potential energy it forms the total mechanical energy, which is conserved under conservative forces. It is also the starting point of the Lagrangian $T - V$ and the Hamiltonian $T + V$.