(J) The SI unit of work or energy.
Definition: The work done by a force of 1 Newton acting to move an object through a distance of 1 meter in the direction in which the force is applied.
Since kinetic energy is one half the mass times the square of the velocity, 1 joule is the kinetic energy of a mass of two kilograms moving at a velocity of 1 m/sec.
The joule is named for the British physicist James P. Joule.

The acoustic power of sound and ultrasound is the energy delivered per unit of time. The power is measured in Watt (W) and is proportional to the square of the amplitude.
1 W = 1 joule/second.

See also Directivity Index, Spatial Average Intensity, and Source Level.

(V) The SI unit of electric potential.
Definition: The amount of potential energy present per unit of charge. 1 volt representing a potential of 1 joule per coulomb of charge.
The unit is named for the Italian scientist Count Alessandro Volta.

(W) The SI unit of power.
Definition: 1 watt is equal to a power rate of one joule of work per second of time or in electrical terms it is the power produced by a current of one ampere flowing through an electric potential of one volt.
Power is the rate at which work is done, or the rate at which energy is expended and is used both in mechanics and in electricity.
The unit is named for James Watt, a British engineer.