Energy, Work, and Power: Physics Concepts and Units

Units of energy

Joules (J), kg•m2/s

Kinetic energy

The energy of motion, determined by the object's mass and velocity.

Gravitational potential energy

Energy stored due to the pull of gravity on an object (can be thought of as its potential to fall), determined by its mass, distance from the ground, and acceleration due to gravity.

Spring potential energy

Energy stored when an elastic object is stretched or compressed and wants to return to its rest length. It is determined by the strength of the spring (spring constant) and the distance it has been distorted.

Principle of the conservation of energy

Energy cannot be created or destroyed, it can only transfer between objects or forms.

Work

The transfer of energy from one object to another as the result of a force being applied. Work is determined by the magnitude of the force and the distance it is exerted over.

Positive work scenario

The work done on a falling tree by gravity as it is cut down.

Negative work scenario

The work a trampoline does on a person when they land on it.

Closed system

Energy and matter cannot enter or leave the system.

Open system

Free exchange of energy and matter between system and surroundings.

Power

Power is the rate of energy transfer over time (or the rate at which work is done).

Units of power

Watts (W).