Energy occurs in a variety of different forms and levels, such as electricity, elasticity, gravity, nuclear energy and electromagnetic radiation. All forms of energy can be categorized in two main classes. One of the main classes happens to be kinetic energy. There are several facts about kinetic energy that apply to all forms of energy.

### Definition

Kinetic energy is defined as the energy of motion. Any object that is in motion -- either vertically or horizontally -- has an amount of kinetic energy. The energy is defined by the amount of work needed to accelerate a given mass from rest (being still) to its current velocity. The mass will maintain its level of kinetic energy until its speed changes. The same amount of work needed to accelerate the mass must be applied in order to decelerate the mass back to rest.

### Rotational Kinetic Energy

Rotational kinetic energy is the energy of a rotating mass, such as the planet Earth, which rotates on an axis. Instead of moving in a vertical or horizontal manner, the mass will rotate in place. The amount of rotational kinetic energy is determined by the body of mass' angular velocity, which is the speed in which the mass is turning on an axis. Other factors that describe rotating kinetic energy is the distance of any mass from a line, and the moment of inertia, which measure the mass' resistance to changes in the rotation.

### Vibrational Kinetic Energy

Vibrational kinetic energy is moving energy that is caused when a mass or object is vibrating. A common example would be a cell phone that vibrates upon receiving a phone call, or an instrument (such as a symbol) being struck. The energy created from the vibrations creates the kinetic energy.

### Translational Kinetic Energy

Translational kinetic energy is the energy created due to motion from one point to another. The amount of translational energy that an object will have depends on two things: the mass of the object and the velocity (or speed) of the object. When creating an equation to determine the amount of translational kinetic energy, the kinetic energy of the object will be directly proportional to the square of its speed.

### Other Facts

Kinetic energy is a scalar quantity. That means that kinetic energy can be fully described by a magnitude (or numerical value) alone. Like work and potential energy, a joule us the standard metric unit for kinetic energy. Kinetic energy's counterpart is potential energy, which is the energy stored in an object, mass or body. As the object, mass or body begins to move, the potential energy is converted into kinetic energy.