The Ability to Do Work
What do a moving car, a hot stove, and a flash of lightning all have in common? They all have energy. In science, energy is defined as the ability to do work or cause change. Energy is not a substance; you can't hold it in your hand. Instead, it's a property that objects have.
The two main types of energy are kinetic energy and potential energy.
Kinetic Energy (KE)
Kinetic energy is the energy of motion. Any object that is moving has kinetic energy. The amount of kinetic energy an object has depends on two things: its mass and its speed (or velocity).
The faster an object moves, the more kinetic energy it has.
The more massive an object is, the more kinetic energy it has (if moving at the same speed).
A speeding train has a huge amount of kinetic energy. A thrown baseball has less. A floating dust particle has very little.
Potential Energy (PE)
Potential energy is stored energy. It's the energy an object has because of its position or state. The object has the potential to do work. There are several forms of potential energy:
Gravitational Potential Energy (GPE): Energy stored due to an object's height above a surface. A book held high in the air has GPE. If you let it go, that stored energy is converted into kinetic energy as it falls.
Elastic Potential Energy: Energy stored in objects that are stretched or compressed, like a stretched rubber band or a compressed spring.
Chemical Potential Energy: Energy stored in the chemical bonds of atoms and molecules. The food you eat, the fuel in a car, and the wood in a fireplace all contain chemical potential energy.
Forms of Energy
Energy can appear in many different forms. All forms of energy are ultimately a type of kinetic or potential energy.
Mechanical Energy: The energy of an object due to its motion or position (the sum of KE and PE). A moving bicycle has mechanical energy.
Thermal Energy (Heat): The total kinetic energy of the particles in a substance. The faster the particles move, the more thermal energy.
Radiant Energy (Light): Energy that travels in waves, like light, microwaves, and X-rays.
Electrical Energy: The energy of moving electrons.
Sound Energy: Energy caused by an object's vibrations, traveling as waves through a substance.
Nuclear Energy: Energy stored in the nucleus of an atom.
Energy Transformation
Energy is constantly changing from one form to another. This is called energy transformation or energy conversion.
Example: When you turn on a lamp, electrical energy is transformed into radiant energy (light) and thermal energy (heat).
Example: When you eat an apple, your body breaks down the chemical energy stored in the apple and converts it into mechanical energy for movement and thermal energy to keep you warm.