Ch. 9 Sec 1 David Fan Mr. Chesbro P-2 I.
What is Energy? A. Energy and Work-Working Together 1. Energy = Ability to do work 2. Work=When a force causes an object to move in direction of force 3. Energy and work are related 1. A tennis player can do work on her racket because she has energy. When she does work on the racket, the racket gains the ability to do work on the ball. Energy is transferred from the tennis player to the racket. When the racket does work on the ball the ball gains the ability to do work on something else. Energy is transferred from the racket to the ball. 4. Both are expressed in joules. When a given amount of work is done, the same amount of energy is involved. B. Kinetic Energy Is Energy of Motion 1. Kinetic energy is the energy of motion 2. All moving objects have kinetic energy. 3. Objects with kinetic energy can do work 1. When you swing a hammer, you give it kinetic energy, which it uses to do work on the nail C. Kinetic Energy Depends on Speed and Mass 1. Kinetic energy = mv2/2 2. The faster something is moving, the more kinetic energy it has 3. The more massive a moving object is, the more kinetic energy 4. Speed has a greater effect on kinetic energy D. Potential Energy Is Energy of Position 1. Potential energy is the energy an object has because of its position or shape. 1. The stored potential energy of the bow and string allow them to do work on the arrow when the string is released E. Gravitational Potential Energy Depends on Weight and Height 1. When you life an object, you do work on it by using a force that opposed gravitational force. As a result, you give that object gravitational potential energy F. Calculating Gravitational Potential Energy 1. Gravitational potential energy=weight x height 2. Since weight is expressed in Newton’s and height is expressed in meters, gravitational potential energy is expressed in Newtonmeters (N x M) or joules G. Mechanical Energy Sums It All Up
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1. Mechanical energy=total energy of motion and position of object 2. Mechanical energy can be all potential energy, all kinetic energy, or some of both 3. Mechanical energy=potential energy + kinetic energy 4. When potential energy increases or decreases, kinetic energy has to decrease or increase in order for mechanical energy to remain constant. 5. The amount of an object’s kinetic or potential energy may change, but its mechanical energy stay the same Forms of Energy 1. All energy involves either motion or position 2. Forms of energy: thermal, chemical, electrical, sound, light, and nuclear energy Thermal Energy 1. All matter is made of particles in constant motion 2. Since the particles are in motion, they have kinetic energy 3. Thermal energy=total energy of particles in object 4. Particles move faster at higher temperatures and have more kinetic energy and thermal energy 5. Particles of a substance farther apart have more energy than particles of the same substance that are closer together 1. Particles in an ice cube vibrate in fixed positions and don’t have a lot of energy 2. Particles in ocean water are not in fixed positions and can move around. Have more energy than ice cube 3. Particles in steam are far apart. They move rapidly, and have more energy than ocean water Chemical Energy 1. Chemical energy=Energy of a compound that changes as its atoms are rearranged to form new compounds 2. Form of potential energy Electrical Energy 1. Electrical energy=Energy of moving electrons ( - particles) 2. The electrons in electrical devices change directions many times per second, bringing energy to different parts 3. The electrical energy created by moving electrons is used to do work 4. Power plants rotate magnets within coils of wire to make elect. 5. Since electrical energy results from the changing position of magnets, electrical energy can be considered potential energy 6. Since electrons move back and forth in a cord, electrical energy can also be considered kinetic energy Sound Energy 1. Sound energy is caused by an object’s vibrations
2. Vibrations cause particles in the air to vibrate. These vibrations transmit energy 3. Sound energy is a form of potential and kinetic energy. To make an object vibrate, work must be done to change its position. 1. When you pluck a guitar string, you stretch it and release it. The stretching changes the string’s position. The string stores potential energy. In the release, the string uses its potential energy to move back to its original position. The moving guitar string has kinetic energy which the string uses to do work on the air particles around it. The air particles vibrate and transmit this kinetic energy from particle to particle. When the vibrating air particles cause your eardrum to vibrate, you hear the guitar. M. Light Energy 1. Not all light can be seen 2. Light energy is produced by the vibrations of electrically charged particles. Unlike sound, the vibrations that transmit light energy don’t cause other particles to vibrate. 3. Light vibrations cause energy to be transmitted N. Nuclear Energy 1. Nuclear energy=Energy associated with changes in nucleus of an atom 2. Nuclear energy is produced in two ways-When two or more nuclei join together or when the nucleus of an atom splits 3. The nuclei of some atoms store a lot of potential energy 4. When work is done to split these nuclei apart, that energy is released 5. This type of nuclear energy is used to generate electrical energy at nuclear power plants