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Energy Notes What is Energy? Energy makes change. Energy moves cars along the road and boats over the water. It bakes a cake in the oven and keeps ice frozen in the freezer. It plays our favorite songs on the radio and lights our homes. Energy makes our bodies grow and allows our minds to think. Scientists define energy as the ability to do work. People have learned how to change energy from one form to another so that we can do work more easily and live more comfortably.
Forms of Energy Energy is found in different forms, such as light, heat, sound and motion. There are many forms of energy, but they can all be put into two categories: kinetic and potential.
Electrical energy is the movement of electrical charges. Everything is made of tiny particles called atoms. Atoms are made of even smaller particles called electrons, protons, and neutrons. Applying a force can make some of the electrons move. Electrical charges moving through a wire is called electricity. Lightning is another example of electrical energy.
Radiant energy is electromagnetic energy that travels in transverse waves. Radiant energy includes visible light, x-rays, gamma rays and radio waves. Light is one type of radiant energy. Solar (sun) energy is an example of radiant energy.
Thermal energy, or heat, is the internal energy in substances––the vibration and movement of the atoms and molecules within substances. Geo-thermal energy is an example of thermal energy.
Motion energy is the movement of objects and substances from one place to another. Objects and substances move when a force is applied according to Newton’s Laws of Motion. Wind is an example of motion energy.
Sound is the movement of energy through substances in longitudinal (compression/rarefaction) waves. Sound is produced when a force causes an object or substance to vibrate––the energy is transferred through the substance in a wave. To sum up what happens to energy when you use a phone to call a friend: 1. The sound energy in your voice makes the air vibrate. Vibrating air carries the sound energy into the phone. 2. The diaphragm in the mouthpiece microphone converts sound energy into electrical energy. 3. The electrical energy travels from the phone, via exchanges, to your friend's phone. 4. A diaphragm in the earpiece loudspeaker of your friend's phone converts the incoming electrical energy back to sound energy. 5. The sound energy travels out from the earpiece into your friend's ear.
Chemical energy is energy stored in the bonds of atoms and molecules. It is the energy that holds these particles together. Biomass, petroleum, natural gas, and propane are examples of stored chemical energy. Ex. H-O-H
Elastic (Mechanical) energy is energy stored in objects by the application of a force. Compressed springs and stretched rubber bands are examples of stored mechanical energy.
Nuclear energy is energy stored in the nucleus of an atom––the energy that holds the nucleus together. The energy can be released when the nuclei are combined or split apart. Nuclear power plants split the nuclei of uranium atoms in a process called fission. The sun combines the nuclei of hydrogen atoms in a process called fusion. Scientists are working on creating fusion energy on earth, so that someday there might be fusion power plants.
Gravitational energy is the energy of position or place. A rock resting at the top of a hill contains gravitational potential energy. Hydropower, such as water in a reservoir behind a dam, is an example of gravitational potential energy.
Law of Conservation of Energy Conservation of energy is NOT saving energy. The law of conservation of energy says that energy is neither created nor destroyed. When we use energy, it doesn’t disappear. We change it from one form of energy into another.
A car engine burns gasoline, converting the chemical energy in gasoline into mechanical energy. Solar cells change radiant energy into electrical energy. Energy changes form, but the total amount of energy in the universe stays the same.
Energy Efficiency Energy efficiency is the amount of useful energy you get from a system. A perfect, energy-efficient machine would change all the energy put in it into useful work—an impossible dream. Converting one form of energy into another form always involves a loss of usable energy.
In fact, most energy transformations are NOT very efficient. The human body is a good example. Your body is like a machine, and the fuel for your machine is food. Food gives you the energy to move, breathe, and think. But your body isn’t very efficient at converting food into usefulwork. Your body is less than five percent efficient most of the time. The rest of the energy is lost as heat. You can really feel that heat when you exercise!
What Does Energy Mean to Us? All organisms must have energy to survive. Photosynthesis is the chemical process that provides that energy! During photosynthesis, the sun’s energy is trapped in the chemical bonds of glucose. Plants (producers) provide us with ENERGY! PHOTOSYNTHESIS Energy Conversion: RADIANT ENERGY is CONVERTED TO CHEMICAL ENERGY! 6CO2 + 6H2O + ENERGY C6H12O6 + 6O2 carbon dioxide water from sunlight glucose oxygen CELLULAR RESPIRATION C6H12O6 + 6O2 6CO2 + 6H2O + ENERGY glucose oxygen carbon dioxide water ATP
RESPIRATION During cellular RESPIRATION the energy is released from it’s chemical bonds for use by the cells. The usable energy form is called ADENSOSINE TRIPHOSPHATE (ATP). Conversions efficiencies are always much less than 100%. At each link in a food chain, a substantial portion of the sun's energy - originally trapped by a photosynthesizing autotroph - is dispersed back into the environment (ultimately as heat). Our bodies convert only about 35% of the energy that it takes in. This may seem inefficient, but our cars are even less efficient.Cars convert about 25% of its energy intake into motion.
Sources of Energy • We use many different energy sources to do work for us. Energy sources are classified into two groups—renewable and nonrenewable. Renewable and nonrenewable energy can be converted into secondaryenergy sources like electricity and hydrogen.
In the United States, most of our energy comes from nonrenewable energy sources. Coal, petroleum, natural gas, propane, and uranium are nonrenewable energy sources. They are used to make electricity, to heat our homes, to move our cars, and to manufacture all kinds of products. These energy sources are called nonrenewable because their supplies are limited. Petroleum, for example, was formed millions of years ago from the remains of ancient sea plants and animals. We can’t make more petroleum in a short time.
Renewable energy sources include biomass, geothermal energy, hydropower, solar energy, and wind energy. They are called renewable energy sources because they are replenished in a short time. Day after day, the sun shines, the wind blows, and the rivers flow. We use renewable energy sources mainly to make electricity.
Energy Calculations The S.I. unit for energy is Joules, J. Kinetic Energy = 1/2 mass X velocity2 KE = mv2/ 2 Example Problem: A 15 kg bicycle carrying a 50 kg boy is traveling at a speed of 5 m/s. What is the kinetic energy of the bicycle (including the boy)?
Gravitational Potential Energy = mass X acceleration due to gravity X height PE = mgh Example Problem: A 0.06 kg tennis ball starts to fall from a height of 2.9 m. How much gravitational potential energy does the ball have at that height?
Example Problem: • Thomas is holding a tennis ball outside a second floor window (3.5 m from the ground) and Dustin is holding one outside a third floor window (6.25 m from the ground). How much more gravitational potential energy does Dustin’s tennis ball have? (Each tennis ball has a mass of 0.06 kg.)
joules potential energy kinetic energy nuclear fusion/fission friction
Thermal Energy All matter is made of tiny particles—atoms and molecules. In all materials—solids, liquids, and gases—these particles are in constantmotion. Like all objects that are moving, these moving particles have kinetic energy. The faster these particles move, the more kinetic energy they have.
The temperature of an object is related to the averagekineticenergy of the atoms or molecules. The faster these particles are moving, the more kinetic energy they have, and the higher the temperature of the object is. The SI unit for temperature is Kelvin (K). The sum of the kinetic and potential energy of all the molecules in an object is the thermalenergy of the object.
***Heat is thermal energy that flows from something at a higher temperature to something at a lower temperature. Heat is a form of energy, so it is measured in joules—the same units that energy is measured in. Heat always flows from warmer to cooler materials.
The amount of heat that is needed to raise the temperature of 1 kg of some material by 1°C or 1 K is called the specificheat of the material. Specific heat is measured in joules per kilogramKelvin [J/(kg K)]. Q = mc∆T Q = thermal energy m = mass c = specific heat of substance ∆T = change in temperature
SPECIFIC HEAT CALCULATIONS • If 150 kilograms of water is heated from 30oC to 40oC, the number of joules of heat energy absorbed is… • If a 2.0 kg sample of water at 5.0oC absorbs 26 J of heat energy, the temperature of the sample will be… Q = mc∆T
HEAT TRANSFERS BY: Conduction—the movement of thermal energy from one object to another when they are in direct contact(touching). Molecules can transfer energy to a neighboring one within an object. • Examples: • Bare feet touching the cement on a hot summer day • Warming up with a hot cup of coffee • Car seat warmers • Can you think of any other examples???
Convection—the movement of thermal energy from one area to another in a liquid or gas. Heat transfers by currents. • Examples: • Wind Currents • Hot Air Balloon • Can you think of any other examples?
Radiation—when warm or hot matter emits electromagnetic radiation – especially infrared radiation – that is then absorbed by an object at a distance. The absorption heats the second object. This energy transfer does NOT require matter. Examples: • A microwave oven • The Sun • UV light Can you think of any other examples?
http://soundcloud.com/educationalrap/sets/radiation-conduction-convectionhttp://soundcloud.com/educationalrap/sets/radiation-conduction-convection
Controlling Heat Flow • Almost all living things have special features that help them control the flow of heat. For example, the Antarctic fur seal’s thick coat and the emperor penguin’s thick layer of blubber help keep them from losing heat. This helps them survive in a climate in which the temperature is often below freezing. In the desert, however, the scaly skin of the desert spiny lizard has just the opposite effect. It reflects the Sun’s rays and keeps the animal from becoming too hot. An animal’s color also can play a role in keeping it warm or cool. The black feathers on the penguin’s back, for example, allow it to absorb as much radiant energy as possible. How do you think humans control body heat flow?
Insulators—a material that does NOT allow heat to flow through it easily. Materials such as wood, plastic, fiberglass, and air are good insulators. Gases are usually much better insulators than solids or liquids.
Conductors—a material that allows heat to flow through it easily. Although conduction can occur in solids, liquids, and gases, solids usually conduct heat much more effectively. Metals such as silver, copper, and aluminum are among the best heat conductors.
A material that is a good conductor of heat, such as a metal, is a poor insulator. Likewise, good insulators are poor conductors of heat. Why do you think most cooking pots are made of metal but the handles usually are not?
Heat Movers—a device that removes thermal energy from one location and transfers it to another location at a different temperature such as a refrigerator and air conditioner.
