Background–Forms of energy – How they are used and produced
Objective
The student knows that energy occurs in many forms and can be observed in cycles, patterns, and systems. The student is expected to explore the uses of energy, including mechanical, light, thermal, electrical, and sound energy.
Foundation
Energy is power…the ability to do work. Every time anything moves, whether it’s the wind, water, cars, trees, people, clocks, or animals, energy makes it happen. All movement is energy. It takes energy to cook a meal, ride a bicycle, speak to a friend, turn on a computer, or listen to a song. We use energy every day. And just like a car cannot run with an empty fuel tank, we need fuel to have the energy to complete tasks. We gain our energy by consuming food. However, energy comes in different forms, all of which provide the power for an object to do work.
Mechanical energy is the energy which is possessed by an object due to its motion or due to its position. Mechanical energy can be in the form of kinetic or potential energy. Kinetic energy is the energy which comes from movement, and potential energy is the stored energy which comes from an object’s placement. A ball flying through the air has mechanical kinetic energy due to its mass and the speed of its movement. A tightly wound spring in a wind up toy has potential (stored) energy which will change to kinetic energy (movement) when the spring is released. The string of a bow when drawn back to shoot an arrow has mechanical (potential) energy, and, when released, changes to kinetic energy to rapidly push the arrow away from the bow.
A fire, a hot cup of coffee, or a heating stove has “thermal” or heat energy. Temperature is really a measure of how much thermal energy an object has. The higher the temperature the faster the particles, or molecules, of an object are moving. A cooking stove heats the air inside the oven and when the cake mixture is placed in the oven, the thermal heat of the air is transferred to the cake and it bakes. A microwave works differently; it uses microwaves (Longer waves in length around a food are the ones that help heat food in the microwave itself.) to make the particles inside the food move more rapidly. The resulting heat from the faster moving particles cooks the food.
Light energy is something we take for granted, but it is becoming even more important than ever. Light is able to travel through space, unlike sound that needs air or some other medium to be transmitted. The portion of the electromagnetic spectrum that humans can see is commonly called “light.” Light energy travels in a straight line, but it can be reflected. Light is reflected when it bounces off a shiny surface, such as a mirror. Light can also be refracted, meaning it can be “bent” when it travels from one medium to another. Because light travels slower in water than in air, a pencil placed in a cup of water will appear broken at the point of entry into the water. Curved lenses in telescopes refract light in order to magnify the picture. Advances have been made even recently to utilize light energy beyond just illumination. Laser lights have become important tools for doctors in surgery, for the manufacture of CD and DVD players and computers, and even for teachers and speakers who use laser pointers in their presentations.
All matter is made up of atoms. Electrical energy is created when electrons, small particles of atoms, are caused to move along a path called a circuit. For the electrons to flow and electricity to be evident, the circuit must be closed, that is to say the path along which electrons are flowing must not be broken, or open, anywhere along the way. When we turn on a light, we are closing an electrical circuit and the lights come on. When we flip the switch off, we open the circuit and the electricity ceases to flow. Materials through which electrons flow easily, such as copper wire, are called conductors, while materials such as rubber or plastic, which do not allow electrons to flow through them as easily, are called insulators. When electricity passes through coils of wire, it can create an electromagnetic field. All electric motors in everything from toy cars to powerful fans use electromagnetic fields to create their power.
When we listen to someone speak, we are doing so because of the effects of sound energy. Sound is created when an object vibrates. The vibration of the object pushes the air molecules nearby, which travel as sound waves to the listener. Our ears are designed to be sensitive to these waves of sound, which our brain translates back into the voice which we hear. Sound waves can be demonstrated by striking a metal rod and feeling the vibration of the ringing rod or by simply placing our hand on our throat and speaking. Sound energy requires a medium such as air or water to transmit, which is why sound does not travel in space.
Energy can be altered or changed within objects to meet the needs of people. We can change the amount of sound energy in a radio or television to adjust the volume up or down. We can adjust the amount of electrical energy in a light bulb if we want a room to be brighter or dimmer. A television is an example of how energy can be changed to meet our needs. A television is powered by electrical energy, but the TV changes the electrical energy into light energy so we see a picture and to sound energy so we hear the voices.
Without sources of energy, the Earth would be a lifeless planet. We have learned how to harness the various forms of energy for our use, and in doing so, we have made our lives more comfortable and enjoyable.