There are different forms of energy
There are many different forms of energy. Think of some things you see around you that use energy. Batteries may power a handheld game or a flashlight. Your toaster and refrigerator are plugged into the wall, which is connected to the power in your house. The power in your house usually comes from the power company, but could come from other sources like solar panels on your roof. You get your energy from food. The thing you are trying to power usually takes its energy from only one, or maybe two forms. For example, a laptop computer can run on its battery, or can run plugged in even with a dead battery. But, if you are tired and want more energy, you can’t plug yourself into a wall! You have to eat food or drink liquid to get your energy.
Energy must be changed into the right form in order to be used
Sometimes we can get energy in one way, but we need to use it in another way. Think of energy companies that extract oil from the ground or mine coal. Our modern houses are set up to run off of electricity. So, in order to use coal as a power source for houses and businesses on the electric grid, we need to be able to turn it into electricity. We don’t burn coal in our houses to heat them or power our toasters! By the time it reaches the outlets in our house, it has already been converted to electricity for us. In order to get the energy we want into the right form we must convert
it. Converting energy means changing energy from one form to another.
Energy cannot be created or destroyed
You might get tired of all the rules in your daily life, but did you know that even science has rules it must follow? One rule is called the “law of conservation of energy”. This law means that energy cannot be created or destroyed. Nothing in nature and nothing that people can do can violate this rule – it’s a rule because it is just not possible to break it. This is the rule that controls the converting of energy. And, it is something engineers must keep in mind when making new things. It means that energy can only change forms, but there is no way for us to create completely new energy or get rid of energy from the world. It must come from somewhere else to start with, or be passed off to something else.
However, there is not a way for us to create a perfect transfer of energy. Some energy is always lost in ways that were not intended, such as the creating of heat, light, or sound. Think of your oven, which you use to heat your food; it also tends to heat your kitchen as well. This is energy intended to heat your food that was lost to the surrounding environment. These small things take away energy that could have been going to a different and more useful purpose. Engineers use words like “efficiency” to talk about how much of the energy goes to the intended use versus being lost in other ways. Engineers think about this loss when designing ways to move or convert energy.
The two major kinds of energy are kinetic and potential energy
Kinetic energy is the energy of motion. When a rollercoaster reaches the bottom of a hill and is going fast it has a high kinetic energy. Electricity is a type of kinetic energy because it is moving energy between tiny particles allowing the electric energy to move. The movement of electric energy is called a current.
Potential energy is the measure of stored energy. It is the work something has the potential to do. A roller coaster has its highest potential energy at the top of the hill. This is because it has the potential to speed up greatly. At the bottom of the hill, it does not have the option to get faster without some extra input because it is closer to the ground. Those things are true because of the force of gravity, which is the force that pulls things to the ground, like a ball that falls to the ground when you let go of it.
When energy moves between kinetic and potential energy it is being converted
As the roller coaster car moves down the hill it loses potential energy and gains kinetic energy. As the speed of the car increases the amount of kinetic energy goes up. As the height of the rollercoaster car decreases, the potential energy goes down.
Since energy cannot be created or destroyed, there is an almost even exchange between kinetic and potential energy. Small amounts of energy are lost in the creation of sound or friction between the roller coaster cars and the track. To read more about friction check out the Machines section.
Power plants and engines convert potential energy into usable energy for machines
Fuels like coal and gas contain potential energy. This energy is released and converted when heated and burned. Combustion is the process of burning fossil fuels to create usable energy. Check out the Machines section for more on combustion.
The energy that comes from your wall plugs is called electricity and is made from power plants. These power plants convert potential energy from many sources into the kinetic energy of electric power. Things in our house that need power get power by plugging into the wall. They may then convert the energy again. For example, kitchen blenders change this electricity into mechanical energy to create the motion of the spinning blades. TVs change electricity into the light and sound needed to create the images and sounds for TV shows.
Food contains a type of potential energy called chemical energy
The way we get energy into our bodies is by eating food. Food contains different kinds of sugars and molecules that are the things that power our bodies (including our brains – you are consuming energy to sit here learning about energy!). Our bodies convert the chemical energy from the food into energy usable by our bodies. Our bodies do this by performing chemical reactions inside of our stomach. This energy is then absorbed into our bloodstreams. Then, we convert this chemical energy into motion and everything we do in our everyday lives. This energy keeps us breathing, our heart beating, our muscles moving, and our brain working.
We get “sugar rushes” after eating too much candy, because candy contains a higher amount of sugar than other foods, and sugar provides a quick source of energy into our blood streams. Because sugar is such a quick source of energy, the energy we get from it is used up quickly, too. A while after eating very sugary foods, you may feel completely wiped out; we call this a “sugar crash”.
Humans can convert energy
After our body converts the chemical energy into energy our body can use, we can then convert the energy again. Whenever you pedal a bike you are converting the chemical energy in your body into mechanical work. You are moving your legs with the chemical energy and this then turns the pedals and creates a forward motion.
When you play baseball you are creating an energy transfer in addition to converting energy. You are using your chemical energy to create kinetic energy and swing the baseball bat. This kinetic energy is then being transferred to the baseball causing it to then move in the opposite direction.
Energy and energy conversion are big parts of engineering
We need energy for engineering. Because it’s not always in the form we need to use it, energy conversion is an important topic in engineering. We convert potential energy in coal, oil, and natural gas to kinetic energy in the form of electricity in our house. We convert the potential energy of the gasoline in the gas tank of our car to the mechanical energy that makes the car move. We convert potential energy of batteries into the kinetic electric energy of handheld gaming devices or mobile phones. And, we convert the potential energy of food into mechanical energy of our bodies by eating food, getting nutrients from it, and using the energy provided by it to fuel our bodies. Energy conversion is everywhere!