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.
Work
The transfer of energy that occurs when a force causes an object to move through a distance.
Kinetic Energy
The energy an object possesses by virtue of its motion, depending on both mass and velocity.
Potential Energy
Energy stored in a system due to the position or configuration of its parts, ready to be released.
Gravitational Potential Energy
Energy stored in an object due to its height above a chosen reference point in a gravitational field.
Elastic Potential Energy
Energy stored in an elastic object that has been stretched or compressed from its natural length.
Conservation of Energy
Energy cannot be created or destroyed, only transformed from one form to another.
Work-Energy Theorem
The net work done on an object equals the change in its kinetic energy — the bridge between force and motion.
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 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 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 to total input energy, expressed as a percentage showing how little is wasted.
Simple Harmonic Motion
Repetitive back-and-forth motion where the restoring force is proportional to displacement.
Conduction
Heat transfer through direct physical contact, where faster-moving particles pass energy to slower neighbors.
Convection
Heat transfer through the movement of a fluid (liquid or gas) carrying thermal energy.
Radiation (Heat Transfer)
Heat transfer through electromagnetic waves (primarily infrared) that travel without needing any medium.