Field Notes • Physics

Energy

Energy is a fundamental concept in physics describing the capacity of a system to do work.

Updated September 11, 20261 min readCited sources

Energy is a fundamental physics concept describing the capacity to do work. It is conserved and measured in joules.

What it is

In physics, energy is the capacity for doing work or producing change in a system. It is a scalar quantity, meaning it has magnitude but no direction. Common sources define it as the ability to exert forces and cause displacement.

Forms of energy

Energy takes many forms, including kinetic (energy of motion), potential (energy of position or configuration), thermal, electrical, chemical, and nuclear energy. These forms can convert into one another while total energy remains constant.

Conservation of energy

A core principle is that energy cannot be created or destroyed, only transformed or transferred. In an isolated system, the total energy stays the same, making energy conservation a key law in physics.

In short

Energy is the capacity to do work.
It is a scalar quantity measured in joules.
Common forms include kinetic, potential, and thermal energy.
Energy is conserved: it cannot be created or destroyed.

Canadian angle

Energy is a core concept in Canadian science education, engineering, and energy policy, including discussions of electricity generation, fossil fuels, hydroelectricity, nuclear power, and renewable energy systems.

Quick questions

What is energy in physics?

Energy is the capacity of a system to do work. It is a fundamental physical quantity used to describe motion, forces, heat, and other processes.

What is the SI unit of energy?

The SI unit of energy is the joule (J).

Can energy be created or destroyed?

In classical physics, the law of conservation of energy says energy cannot be created or destroyed, only transformed from one form to another.

Sources

Encyclopaedia Britannica — https://www.britannica.com/science/energy
Supports: Definition of energy as the capacity for doing work; SI unit joule; common forms of energy.
Oregon State University — https://lipa.physics.oregonstate.edu/sec_introduction_to_energy.html
Supports: Energy as a physical property; scalar quantity; measured in joules.
The Physics Hypertextbook — https://physics.info/energy/
Supports: Energy as the ability to do work; relationship to transfer and transformation; kinetic and potential energy.
EBSCO Research Starters — https://www.ebsco.com/research-starters/science/energy-physics
Supports: Energy as a fundamental property in physics; examples of kinetic, potential, thermal energy; conservation of energy.