Types of Energy
As we cover the different types of energy we will split them into two main groups, potential energy and kinetic energy. We’ll describe the types of energy that fit within each category. Also see what is energy.
Types of Energy
Potential Energy – the energy of position or stored energy – it has the “potential” to do work
Gravitational Energy – This is the energy of position. The higher the position of the object above the ground and the more mass (heaviness) it has the more energy it contains. Gravity is a universal force that acts on all objects. If you drop a bowling ball and a tennis ball from the same height, they will both hit the ground at the same time since gravitational acceleration is constant as discovered by Isaac Newton but their potential energy is quite different based upon the difference in their mass. If one of these balls hits your foot you’d rather it be the tennis ball since it has far less energy to hurt you with when falling under the force of gravity.
Gravitational = Potential Energy = m*g*h = mass * gravity * height
G = 32.174 feet/sec2 (English Units) or 9.81 meters/sec2 (Metric Units)
If you’re using the English constant then be sure that height is measured in feet and mass is in pounds. For Metric, height is in meters and mass is in kilograms. If your height is in inches, simply convert it to feet by dividing by 12 which can be done for all the other units in the equation.
Gravitational energy is the basis of many sports we enjoy like skiing, snowboarding and skate boarding. If you have your skateboard at the top of a large hill and allow it to roll down the hill, you are converting your potential energy which is based upon your position on the hill, to kinetic (motion) energy. Most of the energy is stored in you as you are the far more massive object as compared to the skateboard. If you and your friend both have the same skateboard but he weighs more than you, he will go faster down the hill given his larger mass. When you turn around and walk back you the hill you are replacing the potential energy that you just enjoyed riding down so energy is used to do this. You have to burn your body’s storied chemical energy to walk back up the hill. You feel your body temperature rise as heat is created as your body “burns” glucose.
My favorite use of gravitational energy is the roller coaster. A chain drags the car loaded with people up to the top of the first, and highest hill. The more people in the car, the more mass there is and the faster it goes. When you reach the top of the hill your potential energy is the highest and at the bottom of the hill it’s all kinetic or motion energy. The hills get lower as you go since some of the energy is consumed by friction and heat in the wheels and resistance (drag) from the wind. The excitement comes as potential energy is converted to kinetic energy and you get a bit of a break when the kinetic energy is converted back to potential as the car goes up the next hill. A lot of calculations go into making sure that the car can always make it back to the station but they are based upon the simple formulas we describe in this article.
Chemical Energy – this is energy stored in the bonds of atoms or molecules. Oil (petroleum), coal, natural gas, wood and even corn are common examples of stored chemical energy. Chemical energy is converted to heat energy when we burn these items. A battery stores electrical energy in the form of chemical energy.
Human Body – your body stores energy as chemical energy in the form of glucose, which is blood sugar, and fat. The glucose can be accessed quickly but you can use it up. Athletes call the point where you run out of readily available energy as “hitting the wall”. While fat stores energy it isn’t available as quickly as the glucose is. When you eat, your body converts the chemical energy available in the food to the stored chemical energies of glucose and fat. This stored energy is converted to electricity, heat and muscle operation.
In the movie “The Matrix” machines were using the electricity from humans to generate the electricity they needed to operate since the humans had blackened the sky stopping their solar energy from working.
Mechanical Energy – this is energy created by mechanical devices that are in tension. For example, a compressed spring, or a wound circular spring. Wind-up toys contain springs that when released drive the toys motion:
Nuclear Energy – is the energy stored in the nucleus of an atom. It is the energy that holds the atom together. Large amounts of energy are released when the nucleus is split called fission of when they are combined called fusion. Nuclear energy is interesting because when it operates, unlike burning coal or natural gas, it creates no pollution which might make you think it is a form of green energy. But the fuel that has been used to supply the atoms is highly radioactive and must be safely stored to avoid contamination of the environment. In addition, a nuclear reaction creates a lot of heat which is carried away by cooling water. If the supply of cooling water gets cut off from the reactor and the reaction continues, it becomes a very dangerous situation referred to as “meltdown” which can release deadly levels of radiation. Many people think that the “smoke” that they see coming from a nuclear power plant id radioactive. This is NOT the case. What you are seeing is water vapor from the water that was used to cool the reactor coming from the cooling towers. Some plants are built on lakes and actually transfer the heat to the lake itself. The sun is a large fusion reaction.
The second type of energy is kinetic energy or the energy of motion:
Kinetic Energy – is based on the motion of an object and is a function of how heavy the object is (its mass)and how fast it is moving, its velocity. If a 25 pound one year old child is running to jump on you, you’re probably not going to be too concerned and will let them hit you, but, if a 250 pound football player is running to jump on you, I suspect you’re going to try and move. This is because the energy of the impact will be 10 times higher for the football player moving at the same speed as the one year old. If I throw a b-b at you I don’t think you’ll be concerned, but if I shoot it from a b-b gun then you know it’s going to hurt. The b-b has very little mass but when given a lot of velocity and has a lot more energy. In fact, we would say it has exponentially more energy since velocity is squared in the formula for kinetic energy:
Kinetic Energy = ½ * m*v^2= ½ * mass * velocity^2
Water running in a river or stream, the motion of waves and the wind are all examples of naturally occurring kinetic energy. We use this natural kinetic energy to generate electricity by driving an electric generator. Wind Energy, Hydro (water) Energy and Wave Energy are all considered both green and renewable forms of energy.
Solar Energy (Electromagnetic Energy) – This is sunlight, the energy that is transmitted from the sun to the earth. The sun is an explosion of nuclear energy and some of that energy is converted into wave form (oscillating electrical and magnetic fields) that travel through space to reach the earth. Light is also thought of as packets of energy called photons. Each photon has a specific frequency and wave length associated with it. Yes, light is both a wave and particle but to really understand this gets us into quantum physics and is well beyond the scope of what we are covering here. Sunlight is our largest and most abundant form of energy. It provides heat, the energy to drive photosynthesis that allows plants to grow, and when absorbed by certain materials it creates electricity without any moving parts (solar panels). Solar energy can even burn our skin (sun burn). In our quest to convert to renewable and green forms of energy, solar energy currently has the most potential.
Thermal Energy (Heat Energy) – A hot material has both kinetic and potential energy. As it is heated, the molecules that make it up move and vibrate faster creating kinetic energy and the attraction of the molecules to each other creates potential energy. The higher the temperature, the more thermal energy exists. There was a time when people would warm a large stone by the fire, wrap it in cloth and then place it in their bed to keep them warm. Energy was transferred from the fire to the stone and then slowly to the bed and person in it.
Thermal Mass – In energy efficient building this same concept is used to capture the energy of the sun during the day and slowly release it overnight when it’s cooler. The more thermal mass that is installed, the more heat energy that can be stored in the buildings structure. The thermal mass is typically made up of concrete and lots of it. Concrete floors and walls get hit by the sun during the day and as they warm up they gain thermal energy. This energy transfers to the air in the room and they cool. This form of heating is referred to as Passive Solar Heating.
Electrical Energy – is the motion of electrons from one atom to the next in the presence of an electrical field. This creates a chain reaction conducting electrons through the material. The kinetic energy of the electrons is the source of their energy. As the electrons move from atom to atom, energy is transmitted to the atom and heat is created. If you’ve ever used a small extension cord to power something that consumes a lot of electricity, like a power saw, you’ll be surprised to find that the cord itself is getting hot (please don’t attempt this as an experiment as it is dangerous and can start a fire).
In a traditional incandescent light bulb the thin heated wire glows giving off both heat and light. This is why you can burn yourself by touching a light bulb that has just been turned off. All that heat that comes with the light is wasted energy, especially in the summer when it is working against the air conditioning. A florescent light excites a gas with the electron flow and it glows giving off a blue colored light but very little heat and therefore requires less electrical energy to operate. We don’t like this light as much and we say it is colder. Incandescent lights are said to give off a warm glow and make us feel good which is probably based on all the years humans only had fire to provide light. LED bulbs are an attempt to provide even higher levels of energy efficiency and a warmer light source and we will see them improve as scientists and engineers fine turn the wavelengths of light they give off. It is said that it took Thomas Edison 1,000 tries to get the incandescent bulb right but I expect with our knowledge and resources LED’s will get there faster.
So how do we generate electrical energy?
For electrons to move, we must have a material in which electrons are loosely attached to the atoms of the material. We call these types of materials conductors. Metals conduct electricity well. Plastics, rubber and wood atoms have strong bonds with their electrons and are not good at conducting electricity so we call them insulators. To create electrical wires copper is used since it is an excellent conductor and is flexible. It is wrapped in a plastic sleeve since the plastic is an excellent insulator.
So how do we get the electrons to move? This is most often done with the motion of a magnetic field around a wire. The moving magnetic field causes the electrons to be excited and move from atom to atom. A device that moves the magnetic field and causes electrons to move is called a generator. Generators are powered by many of the other forms of energy that we have described. Hydro-Electric power generation at Niagara Falls.
Sunlight also causes electrons to move in certain materials. When we create a large surface of these materials it can absorb more sunlight and create more electricity. We call these solar panels and they have no moving parts. Scientists and engineers are working to make them more efficient (creating more electricity for the same amount of sunlight) and less expensive to manufacture. See how solar panels work.
It wouldn’t be a complete discussion of types of energy with talking about renewable and green energy. These terms have become very popular recently:
Renewable Energy – typically defined as energy that can be easily replaced. We can grow more trees and corn, and there is an unlimited supply of sunlight and the wind continues to blow and waves continue to move. Oil, Natural Gas and Coal are assumed to be non-renewable since they took millions of years to form they won’t be easily renewed once we use them up.
Green Energy – is a little more loosely defined as energy sources that do not do damage to the earth. They are called green as it is assumed that the planet remains “greener” when we use them. Burning oil, wood, or natural gas creates hydro-carbons which damage the ozone layer and are referred to as green house gases. Natural Gas burns cleaner than oil but is not considered green but is instead referred to as a “clean” energy. Solar, wind and wave energy are considered green energy since they are not seen as creating pollution and damaging the planet. Some people consider the energy used in manufacturing solar panels, wind turbines and batteries for electric cars when trying to decide if an energy is green.
Might also be of interest: What is a Kilowatt?