Kinetic energy is the energy that an object possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity. Once the object has reached this velocity, it maintains this kinetic energy unless its speed changes. Kinetic energy is a scalar quantity, meaning it only has magnitude and no direction. It is one of the two main forms of mechanical energy, the other being potential energy, which is the energy stored in an object due to its position or configuration.

In different contexts, kinetic energy can take on different forms, such as translational kinetic energy (due to linear motion), rotational kinetic energy (due to rotational motion), and vibrational kinetic energy (due to the vibration of particles within an object).