The word “energy” is used to describe many different things—how we heat and cool our homes, how we fuel cars, and even how we’re feeling on a day. Energy isn’t something that can be seen or felt, but you can see and feel the effects when energy is transferred from one place to another.
Energy is what makes change happen and can be transferred form one object to another. Energy can also be transformed from one form to another.
Power is the rate at which energy is transferred. It is not energy but is often confused with energy. The watt is the most commonly used unit of measure for power. It measures the rate of energy transfer.
Click on a scenario number above to begin the interactive explainer.
A watt equals a joule per second. If a smart phone uses five joules of energy every second, then the power of the phone is five joules per second, or five watts.
The animation above demonstrates the difference between energy and power. Each slide in the animation will transfer energy at different rates for five seconds. If each child represents one unit of energy, which slide has the highest power?
This animation is featured in our Energy e-book series. Click on the thumbnails below to download our free e-books or subscribe to our iTunes U course. You can also visit our e-books page to view our other offerings.
Explore how humans use energy — from generating electricity to developing energy-efficient technologies.