Energy Systems
18 concepts in Physics
Energy is one of the most fundamental and unifying concepts in all of science. This topic explores what energy is, the forms it takes — kinetic, potential, thermal, chemical, electrical, nuclear — and how it transfers and transforms within systems. Students learn the law of conservation of energy, which states that energy is never created or destroyed, only converted from one form to another. They study work and power as quantitative measures of energy transfer, and they investigate efficiency and energy loss due to friction and heat. Understanding energy systems allows students to analyze everything from a bouncing ball to a power plant to the metabolism of a living organism. These ideas provide essential context for discussions about renewable energy, climate change, and sustainable technology.
Suggested learning path: Start with identifying forms of energy and energy transfers in everyday situations, then study conservation of energy quantitatively, followed by work, power, and efficiency calculations.
Energy
The capacity to do work or cause change in a physical system, measured in joules (J).
Work
The transfer of energy that occurs when a force causes an object to move through a distance in the direction of the force, calculated as.
Kinetic Energy
The energy an object possesses by virtue of its motion, equal to one-half times its mass times the square of its velocity.
Potential Energy
Energy stored in a system due to the position or configuration of its parts, ready to be converted into kinetic or other forms of energy.
Gravitational Potential Energy
Energy stored in an object due to its height above a reference point in a gravitational field: $PE = mgh$.
Elastic Potential Energy
Energy stored in an elastic object that has been stretched or compressed from its natural length.
Conservation of Energy
A fundamental law of physics stating that the total energy of an isolated system remains constant over time — energy can be transferred between objects.
Work-Energy Theorem
The net work done on an object by all forces acting on it equals the change in its kinetic energy.
Power
The rate at which work is done or energy is transferred, measured in watts (joules per second).
Mechanical Energy
The total of kinetic energy and potential energy in a mechanical system at any given moment.
Thermal Energy
The total kinetic energy of all particles (atoms and molecules) in an object due to their random motion.
Heat Transfer
The spontaneous flow of thermal energy from a hotter object to a cooler one until they reach thermal equilibrium (the same temperature).
Temperature
A measure of the average kinetic energy of the particles in a substance, determining how hot or cold it is.
Efficiency
The ratio of useful output energy (or power) to total input energy, expressed as a percentage — always less than 100% due to energy losses.
Simple Harmonic Motion
Oscillatory motion where the restoring force is proportional to displacement from equilibrium, producing sinusoidal position over time.
Conduction
Heat transfer through direct physical contact between particles, where faster-moving (hotter) particles collide with and pass kinetic energy to slower-moving (cooler) neighbours.
Convection
Heat transfer through the bulk movement of a fluid (liquid or gas) that carries thermal energy from one place to another.
Radiation (Heat Transfer)
Heat transfer through electromagnetic waves that require no medium — the only form of heat transfer that works through a vacuum.