What Is a Joule?
A joule (symbol: J) is the standard unit of energy or work in the International System of Units (SI). It is defined as the amount of work done when a force of one newton is applied to an object, moving it a distance of one meter in the direction of the force.
Section 2: Defining the Joule Mathematically
The joule is a derived unit, combining fundamental units of mass, length, and time. One joule is equivalent to one newton-meter (N·m). Because a newton is a kilogram-meter per second squared (kg·m/s²), a joule can also be expressed as one kilogram-meter squared per second squared (kg·m²/s²).
Section 3: A Practical Example of a Joule
A single joule represents a very small amount of energy. For example, it takes approximately one joule of energy to lift a small apple (which weighs about one newton) a height of one meter. Similarly, the heat energy released by an average person at rest is about 100 joules every second.
Section 4: Why Is the Joule Important?
The joule is a universal and standardized unit that allows scientists and engineers across all disciplines—from mechanics and electricity to chemistry and thermodynamics—to measure and compare energy consistently. It provides a common language for quantifying work, heat, and all other forms of energy.