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    Home / Science lessons / What is Energy?
    • What is Energy?

      You wouldn't be using your computer if it weren't for energy in many different forms! The clack of fingers hitting the keyboard is what you hear when energy reaches your ears in sound waves. The light from your computer monitor is energy. Electric energy from a power cord or battery makes your computer work. Your body is 'powered' by chemical energy in the food you eat. Your hands can feel heat energy coming from the warm monitor or bottom of the laptop. That's a lot of energy! But what are all these 'energy' forms and where do they come from? Keep reading to find out.

      Energy is usually defined as 'the ability or capacity to do work.' Work is the transfer of energy, usually defined as force applied over distance or force x distance. Energy is measured in joules (1 newton of force applied over 1 meter distance) or foot-pounds (1 pound of force applied over 1 foot of distance). Power is the rate of doing work or transforming energy from one form to another. Power is measured in watts (1 joule per second) or horsepower (550 foot-pounds per second). So a 60 watt light bulb converts 60 joules of electrical energy per second into light and heat energy. If you lift a box you are using energy from your body to do work.

      The different forms of energy can be classed as either potential or kinetic. Potential energy is being stored, ready to do work. If a pencil is resting on the table, it has potential energy. If it falls from the table, that potential energy has been changed into kinetic energy, the energy of motion (with a boost from the kinetic energy of whatever gave it a push). When the pencil hits the floor, some of its kinetic energy disperses. Eventually all of the pencil's kinetic energy is transferred to the floor and it stops rolling. Once it's settled on the floor, it no longer has potential or kinetic energy. If you come along and move the pencil, your potential energy has been turned to kinetic energy, not the pencil's! This transfer of energy from one form to another without changing the total amount is called the conservation of energy. This ties into the first law of thermodynamics, which states that energy cannot be created or destroyed - it can only change form.

      The Electromagnetic Spectrum

      You are probably already familiar with energy called electromagnetic radiation, even if you've never heard the term before. Visible light, x-rays, microwaves, radio waves, and the ultraviolet radiation that gives you a sunburn are all different types of electromagnetic (EM) radiation. So what is EM radiation? Basically it's a stream of tiny electrically-charged particles called photons, which travel in waves. They actually move in a special type of wave, called a transverse wave: one that doesn't need a medium like air or wire to travel through. This means that EM radiation can travel through the vacuum of space. All electromagnetic waves can travel at the same speed, the speed of light, which is about 186,000 miles per second! However, they only travel at maximum speed through a vacuum; things like water and air slow them down.

      Transverse waves have oscillations (up and down or side to side movement) that are at right angles to the direction their energy is traveling. Since the electromagnetic spectrum is also made up of photons, it can act as either a stream of particles or as a wave. EM radiation is made of electrical fields and magnetic fields together.

      Each type of EM radiation has different wavelengths and frequencies. Frequency is the number of waves in a given time. The shorter the wave, the higher the frequency. And the higher the frequency, the higher the amount of energy in the wave. Wavelength refers to the distance between each complete wave cycle (e.g., two peaks right next to each other).

      The sun is the source of much of the energy on this planet. Unlike the earth, the sun is not a solid; instead, it is a huge ball of gas, composed mainly of hydrogen. Every second, the tiny nuclei (plural of nucleus) of tons of atoms fuse together to form molecules. Huge amounts of energy are released in the process. This energy is in the form of electromagnetic radiation.


      Heat energy is often transferred by infrared electromagnetic radiation. It is at a wavelength invisible to our eyes, but our skin can sense it. Heat energy can only be kinetic, since it is energy of moving particles. The increased energy from the transfer makes molecules speed up. As they move faster, they bump into each other and spread out. Enough heat can break the bonds that hold molecules together as a solid, so they become a liquid. Add more heat and the liquid will become a gas.

      Heat moves from hot temperatures to cold temperatures. It keeps moving until all the molecules around it are the same temperature (somewhere in between the original temperatures that were mixed). This evened-out state is called thermal equilibrium. If you give a cup of oil and a cup of water an equal amount of heat, the oil will get hotter because it has a different thermal capacity - its molecules move faster.

      Temperature is the measure of how hot or cold something is, based on how fast or slow its molecules are moving. Two commonly used temperature scales are Celsius (C) and Fahrenheit (F). The freezing point of water is 0°on the Celsius scale and 32°on the Fahrenheit scale; its boiling point (when it turns into vapor) is 100°C and 212°F.


      Light is electromagnetic radiation in the middle of the spectrum. Its wavelengths are medium-sized, the only wavelengths that our eyes can detect. All of the colors of the rainbow are part of the visible light set of the electromagnetic spectrum. Red-colored light has the longest wavelength (just short of infrared) and violet-colored light has the shortest wavelength (just longer than ultraviolet radiation).

      The sun and other hot sources produce incandescent light, which is light energy converted from heat. Fireflies, glow light sticks, and fluorescent bulbs convert other kinds of energy to light without using much (or any) heat.

      • Find out more about light energy in the Light & Optics issue of this newsletter.


      Sound travels in longitudinal waves, which requires a medium, such as air, in order to travel. These are also compressional waves, formed when air is pushed away and then clumped together with empty spaces in between. Use a slinky to demonstrate how these waves work. Have someone hold one end of the slinky, and you hold the other. Spread apart so that the slinky is stretched out to about half its length. Now push your end of the slinky straight out toward the other person. The coils of the slinky will also push forward in bunches as the 'wave' ripples down the length of the slinky. When these waves go through your ear and are processed in your brain, they are converted to sound that you can hear.


      Chemical energy is potential energy stored in the chemical bonds that join atoms together. It can be converted to electrical, heat, or other energy through chemical reactions that break the bonds.

      Food is a source of chemical energy. Our bodies store the potential energy until we need it. For example, when you sit down at the computer, your body converts some of chemical energy to another form, enabling you to move. Other common sources of chemical energy are gasoline and batteries.


      Mechanical energy is associated with the movement or potential movement of an object. Springs and rubber bands have elastic potential energy; when they are stretched out they have the potential to shoot across the room when released. There is also gravitational potential energy, the energy something has because of its position above the ground. For instance, when you are holding a ball, it has potential energy from the force of Earth's gravity pulling on it. If you release it, the potential energy will be converted to kinetic energy as it falls. The closer the ball gets to the ground, the more kinetic energy and the less potential energy it has.


      Nuclear energy comes from fission, the splitting of atoms, or fusion, the joining of atoms. Nuclear power plants use fission; the sun releases energy through fusion. One kind of uranium, U-235, is 'unstable.' When a stray neuron comes along, the unstable U-235 atom absorbs the neuron and then breaks apart into two atoms and more loose neurons. A lot of energy is released in the process. In nuclear power plants, this is used to produce power: fission is induced, which releases heat energy, which causes steam, which turns the power plant's turbines, which powers its generators, which provides electrical power to the area.

      Right now a hot topic is whether we should be using more renewable energy sources than nonrenewable ones. Sources of renewable energy are ones that we use without using up them. Some examples are the sun (in sunny climates, solar panels can capture its energy), wind (we can use its energy with windmills), and water (providing power through hydroelectric dams). Nonrenewable sources of energy, such as oil and coal, could eventually be used up; they aren't being continually replaced the way that renewable sources are.

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