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How Energy Works

You might think that your physics assignment is “work” – but a physicist would disagree with you!

Work, in physics, is what happens when you apply force to an object and move it over a distance. Work can also be defined as a transfer of energy from one object to another object. Energy – by the physics definition – is simply the ability to do work! This may sound confusing, but stick with us…

For example, an electric car has energy stored in its battery. When you drive an electric car, the motor uses energy to move the wheels. At the end of the trip, the battery has less stored energy than it did at the beginning of the trip.

Where did the energy in the car battery go? The Law of Conservation of Energy can tell us…

The Law of Conservation of Energy

The law of the conservation of energy states that there is a fixed amount of energy in the universe. Energy cannot be created, and energy cannot be destroyed. Energy can only be transferred from one object to another.

Energy transfers happen through two processes: work and heat. When electricity passes through a power line, some of the electrical energy becomes heat. The rest of it arrives at your house to do work. It powers the lights, keeps the refrigerator cold, and creates microwaves so you can heat up your lunch.

You can also think of energy transfers that happen when you do exercise. The energy stored in your cells becomes movement. For instance, to pick up a heavy weight or run a mile, your muscles are converting stored energy. Most of the energy works to move your muscles, while some of it becomes heat. This is part of the reason you can get hot and sweaty while you work out!

Let’s check out all the different forms that energy can take:

Potential Energy

Potential energy is a type of energy that is stored. A battery has potential energy. If you put that battery into a flying drone, the drone converts the battery’s potential energy into the energy of movement – kinetic energy. This spins the blades of the drone and allows it to take off and fly around your house. (It may also have the energy to drive your mom crazy…)

You can also think of potential energy as a large bowling ball sitting on a shelf. To get the ball onto the shelf, you must use energy to pick it up. As you set it on the shelf, the energy is transferred to the bowling ball. If the ball falls from this shelf, the energy would crash into the floor and make a dent. But, as the ball is sitting on the shelf, this energy is still just potential energy. Until the ball starts to fall, this energy is stored and cannot do work (or damage to the floor).

Try this: stretch a rubber band so it’s tight. Hold it steady. You have just transferred energy into the rubber band. In other words, the rubber band now has potential energy. Now, let the rubber band go!

The potential energy becomes kinetic energy as the rubber band flies out of your hands.

Kinetic Energy

While the rubber band was stretched out, it was full of potential energy. But, the stretched out rubber band wasn’t doing any work. Once you released the potential energy, that energy was converted into kinetic energy – also known as moving energy. The kinetic energy moved the rubber band across the room. Kinetic energy does work – it moves objects over distances.

This energy of motion can overcome other forces that act on objects. Kinetic energy can do the work to overcome friction and slide a chair out from the table. Kinetic energy gives you the power to do the work of resisting gravity by lifting something off the ground or jumping in the air.

While potential energy and kinetic energy can do work – what about all that energy lost to heat?

Thermal Energy

Thermal energy is the energy of heat. Remember how we said that some of the energy in an electric car is lost to heat? This “loss” is simply electrons that escape from the electrical circuits in the car. These electrons run into other atoms, transferring their energy to the atoms and making them move faster.

When atoms start to move fast and run into each other, they get hot. In most physical processes, at least some potential energy is converted to heat as the rest is converted to kinetic energy.

There are many different ways of generating heat energy. For example, electromagnetic energy from the sun heats the air by making the air molecules move faster. Some devices, like an electric stovetop, create heat energy on purpose. This heat is transferred into your food, which helps you cook.

Incandescent light bulbs transferred most of their energy to heat rather than light. These bulbs did produce lots of light, but the bulbs would also get very hot to the touch. Incandescent light bulbs used energy inefficiently. Modern LED light bulbs put most of their energy toward making light. They don’t create much thermal energy, so they don’t get too hot to touch.

Electromagnetic Energy

Electromagnetic energy is a form of energy that comes in waves. It is also called electromagnetic radiation. There are quite a few types of electromagnetic energy, including radio waves, infrared and ultraviolet light, and X-rays.

You can even create electromagnetic energy yourself! Simply put some food in a microwave oven. These devices use microwaves, a type of electromagnetic energy, to heat our food. The microwaves are created by converting electrical energy into the energy in microwaves. Microwaves cause water molecules to vibrate, which transforms the wave energy into heat energy.

Comic: Where did the energy go?

Written by Laura McCamy

Edited by Gabriel Buckley, MS Professional Natural Sciences

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