When we talk with friends about energy, sometimes we’re talking about how tired or invigorated we feel. Other times we’re referring to how much charge is left in the battery on our phones. But in science, the word energy has a very specific meaning. It refers to the ability to perform some type of work on an object. That could be lifting the object off the ground or making it speed up (or slow down). Or it could be kick-starting a chemical reaction. There are lots of examples.
Two of the most common types of energy are kinetic (Kih-NET-ik) and potential.
Kinetic energy
Every object in motion has kinetic energy. This could be a car zooming along the highway, a soccer ball flying through the air or a ladybug slowly walking along a leaf. Kinetic energy depends on just two quantities: mass and speed.
But each has a different impact on kinetic energy.
For mass, it is a simple relationship. Double something’s mass and you’ll double its kinetic energy. A single sock tossed toward the laundry basket will have a certain amount of kinetic energy. Ball up two socks and toss them together at the same speed; now you’ve doubled the kinetic energy.
For speed, it’s a squared relationship. When you square a number in math, you multiply it by itself. Two squared (or 2 x 2) equals 4. Three squared (3 x 3) is 9. So if you take that single sock and throw it twice as fast, you’ve quadrupled the kinetic energy of its flight.
In fact, this is why speed limits are so important. If a car crashes into a light post at 30 miles per hour (about 50 kilometers per hour), which might be a typical neighborhood speed, the crash will release a certain amount of energy. But if that same car is traveling 60 miles per hour (nearly 100 kilometers per hour), like on a highway, the crash energy hasn’t doubled. It’s now four times as high.
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