What Is Energy?

lightbulb coils burning with electricity

The Definition of Energy

Energy refers to the ability or capacity to do work or cause changes in a physical system. 

Most people think of energy as the “fuel” or “power” that allows things to happen or work to be done. It can be converted from one form to another, but it is never created or destroyed. Instead, it is transferred or transformed from one object or system to another. When you switch on a light bulb, electrical energy is converted into light energy.

Energy is a fundamental concept in physics and encompasses various forms that exist in our everyday lives, including kinetic energy, thermal energy, nuclear energy, potential energy, chemical energy, electrical energy, mechanical energy, heat energy, light energy, gravitational energy, radiant energy, and even sound energy. 

In this article we’ll mainly focus on the different types of energy used to power our homes and businesses, but it’s worth examining all types at the start. 

Different Forms of Energy

For example, when you burn a piece of wood, the chemical energy in the wood is converted into heat energy. The heat energy can then be used to cook food, heat your home, or generate electricity.

  • Kinetic energy is the energy possessed by an object in motion. Think of a wind turbine that converts the power of movement into electricity. 
  • Thermal energy, on the other hand, refers to the energy associated with the temperature of an object or substance. When we heat water on a stove, the thermal energy increases, causing the water to boil.
  • Nuclear energy is derived from the process of nuclear reactions, like those that occur in the core of a nuclear power plant or during a nuclear explosion. 
  • Chemical energy refers to the energy stored within the bonds of atoms and molecules. When chemical reactions occur, such as the combustion of fossil fuels like natural gas, the stored chemical energy is converted into other forms, such as heat and light energy.
  • Electrical energy is the result of the movement of electric charges. It powers our devices and lighting systems, allowing us to use electricity for various purposes. 
  • Heat energy, also known as thermal energy, is the energy transferred between objects due to temperature differences. When you touch a hot stove, the heat energy transfers to your hand, causing it to feel hot. 

How Energy Is Measured

There are a number of ways energy can be measured, depending on the context and form of energy used, including: 

  • Joule (J): The joule is the SI (International System of Units) unit of energy. It’s defined as the amount of energy transferred when a force of one newton is applied over a distance of one meter. The joule is a versatile unit and can be used to measure various forms of energy, including mechanical, thermal, and electrical energy.
  • Kilowatt-hour (kWh): The kilowatt-hour is a unit commonly used for measuring electrical energy consumption. It represents the amount of energy consumed when a power of one kilowatt is used for one hour. It’s widely used in utility bills to measure electricity usage.
  • British Thermal Unit (BTU): The British Thermal Unit is a unit of energy commonly used in the United States, particularly in the field of heating and cooling. It’s defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. One BTU is approximately equal to 1,055 joules.
  • Electronvolt (eV): The electronvolt is a unit of energy commonly used in particle physics and atomic physics. It’s defined as the amount of energy gained by an electron when it’s accelerated through an electric potential difference of one volt. One electronvolt is approximately equal to 1.602 x 10^-19 joules.