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Kinetic Energy: Examples, Definition & Quiz

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Elizabeth Basa

To knock down a set of bowling pins, what must be true about the bowling ball? It must be moving! This lesson discusses the energy perspective of this simple truth.

Kinetic Energy and Motion

Would you believe me if I told you that, without kinetic energy, there would be no music in the world? No food? No life? This lesson will explain why.

When you think of a moving object, what comes to mind - a person walking down the street or the moon orbiting Earth? Perhaps cars racing on a track or the whipping wind of a massive storm? If we tried to list all objects in motion, or objects that are capable of motion, we would find that absolutely every piece of matter in existence would be on that list.

You might be thinking that, at the moment, your desk is not moving and neither are your walls for that matter. Sure a desk can fall down the stairs and walls can crumble, but presently, they do not seem to be moving. Yet, if we think carefully about the atoms that make up these objects, you will realize that, because motion exists in every atom (since electrons orbit every nucleus), so does motion exist in every object. Of course motion can happen in a myriad of ways, from atomic to planetary and everything in between.

So what does all of this motion have to do with kinetic energy? Here it is: motion is kinetic energy. Kinetic energy is the energy something has because it is moving. With energy, things can do work. The bowling ball only knocks over the pins because of its movement, or kinetic energy.

The kinetic energy of the ball knocks over the pins.
The kinetic energy of the ball knocks over the pins.

A wrecking ball demolishes a building because it is in motion. Liquid water becomes steam because the molecules move faster and faster until they change phase. Every cell in your body was built and functions with moving parts. Can you see how endless this is? Kinetic energy has that much of a massive presence in the universe. It is that integral to both life on Earth and to how non-living objects interact and impact other things.

Factors Affecting Kinetic Energy

Does every moving object have the same amount of kinetic energy? Let's think about bowling again. If you rolled a golf ball down the bowling lane at the same speed of an average bowling ball, would the pins still fall? Probably not. What about a pea? Definitely not. This tells us that how much kinetic energy something has is clearly related to its mass. Would you flinch at the kinetic energy of a falling feather?

Objects with less mass have less kinetic energy than objects with more mass moving at the same speed.
Objects with less mass have less kinetic energy than objects with more mass moving at the same speed.

Now imagine the golf ball were shot down the bowling lane at supersonic speed. It then becomes very likely some pins would fall or at least the one pin hit by the fierce projectile. This tells us how much kinetic energy an object has also has something to do with its speed. Mass and speed both are factors in the quantity of kinetic energy that moving objects have. Fluffy feathers have such little mass that, even at high speeds, it is hard for them to have a lot of kinetic energy. Cars can have both large amounts of mass and speed and can therefore have a lot of kinetic energy.

A fast-moving car has a large amount of kinetic energy. This is why car accidents are so dangerous.
A fast-moving car has a large amount of kinetic energy. This is why car accidents are so dangerous.

Types of Kinetic Energy

Kinetic energy can be categorized into different types based on various forms of motion. For example, vibrational kinetic energy is the energy of motion generated by objects that vibrate, such as the strings of a violin. Rotational kinetic energy describes the energy of motion of an object rotating, such as a wheel. Kinetic energy can even be passed from one object to the next, as we've seen with our bowling example; this is called translational kinetic energy.

Summary

All energy in the universe falls into two main types: kinetic and potential. Potential energy, which is discussed in another lesson, is energy being stored. Kinetic energy is the energy of motion. Any object in motion has kinetic energy and is using kinetic energy every moment it is moving. Kinetic energy can vary in quantity depending on the mass of an object and how fast it is moving.

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