Knowledge you can walk. Read the idea below, then step up to the general, across to peers or down to the specific.
Physical
Energy Forms
Energy comes in several forms, such as motion, stored energy, heat and light, and it can change from one form to another.
Learn, discuss, create, buy or invest
The idea
Energy is the ability to do work, like lifting a box, warming a room or lighting a street. Scientists sort it into forms based on where it is and what it is doing. A moving object has kinetic energy. An object can also store potential energy because of its position, such as a rock at the top of a hill. Food and fuel hold chemical energy that is released in chemical reactions. Light carries radiant energy.
The most important rule about energy is that it is never created or destroyed in an isolated system. The total amount stays the same, and the energy simply changes from one form into another. When you ride a bicycle downhill, energy stored by your position turns into motion. When you rub your hands together, the motion of your skin produces heat through friction. A power plant turns one form into electrical energy that can travel through wires. These forms are not separate boxes, and one object can hold several at once.
Energy is measured in a unit called the joule. All living things take in energy and give it off, and sunlight is the main source that drives Earth's climate and living systems. Learning the forms of energy helps explain everything from a bouncing ball to a thunderstorm.
Check yourself
Question 1 of 2
What happens to the total energy of an isolated system over time?
Composition
what it's made of
- Kinetic energy — The energy an object has because it is moving.
- Potential energy — Energy stored by an object, for example because of its position.
- Chemical energy — Energy held in substances and released or absorbed in chemical reactions.
- Radiant energy — Energy carried by light and other electromagnetic radiation.
- Internal and thermal energy — Energy held inside a substance, which we feel as heat.
- Elastic energy — Energy stored in a stretched or squeezed solid, like a spring.
Connection
how it relates
Under Physical
Change
how and why it evolves
- Past
- The word energy comes from an ancient Greek word meaning activity. Over time, scientists learned that heat, motion and light are all forms of the same quantity, which led to the law of conservation of energy.
- Now
- Today energy is measured in joules, and engineers design machines and power plants around turning energy from one form into another.
- Next
- Much future work will likely focus on capturing and storing energy from sunlight and wind more efficiently, though which methods win out is still uncertain.