Physics A.3 Work, Energy and Power

Conservation of energy

The principle that the total energy of an isolated system remains constant, though it may change forms. Energy can neither be created nor destroyed, only transferred or transformed.

Work

The transfer of energy that occurs when a force is applied to an object and the object is displaced in the direction of the force, given by W = Fs cos(θ).

Sankey diagram

A graphical representation of energy flows within a system, showing the magnitudes of energy transfers and transformations between different forms of energy.

Mechanical energy

The sum of an object’s kinetic energy and potential energy, including kinetic energy (Ek = 0.5mv²), gravitational potential energy (ΔEp = mgh), and elastic potential energy (EH = 0.5kx²).

Power

The rate at which work is done or energy is transferred, given by P = ΔW/Δt = Fv.

Efficiency

A measure of how effectively a system converts input energy into useful output energy, given by η = Eoutput / Einput = Poutput / Pinput.

Energy density

The amount of energy stored in a given system or region of space per unit volume, typically measured in joules per cubic meter (J/m³).