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# Unit 3 pp #1 7th grade

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### Unit 3 pp #1 7th grade

1. 1. Section 1 What is Energy?<br />Chapter 19<br />Energy and Work: Working Together<br />In science, energy is the ability to do work.<br />Work is done when a force causes an object to move in the direction of the force.<br />A tennis player does work on a racket by exerting a force on it. The racket does work on the ball.<br />
2. 2. Section 1 What is Energy?<br />Chapter 19<br />Energy and Work: Working Together, continued<br />When one object does work on another, energy is transferred from the first object to the second.<br />This energy allows the second object to do work.<br />So, work is a transfer of energy.<br />
3. 3. Section 1 What is Energy?<br />Chapter 19<br />Energy and Work: Working Together, continued<br />Like work, energy is expressed in units of joules (J).<br />There are many different kinds of energy, and all can be measured and compared.<br />
4. 4. Section 1 What is Energy?<br />Chapter 19<br />Kinetic Energy<br />Kinetic energy is the energy of motion.<br />All moving objects have kinetic energy.<br />Kinetic energy can be used to do work. For example, kinetic energy allows a hammer to work on a nail.<br />
5. 5. Section 1 What is Energy?<br />Chapter 19<br />Kinetic Energy, continued<br />Mass and Speed The amount of kinetic energy that a moving object has depends on the object’s mass and speed.<br />The faster an object is moving, the more kinetic energy it has.<br />The more mass an object has, the greater its kinetic energy.<br />
6. 6. Section 1 What is Energy?<br />Chapter 19<br />Kinetic Energy, continued<br />Speed has a greater effect on kinetic energy than mass does.<br />A truck with twice the mass of a car but moving at the same speed has twice the amount of kinetic energy.<br />But if the speed of the car doubles, its kinetic energy increases by four times.<br />
7. 7. Section 1 What is Energy?<br />Chapter 19<br />Potential Energy<br />Potential energy is the energy an object has because of its position.<br />For example, a stretched bow has potential energy because work has been done to change its shape.<br />The energy of that work is turned into potential energy.<br />
8. 8. Section 1 What is Energy?<br />Chapter 19<br />Potential Energy, continued<br />Gravitational Potential Energy When you lift an object, you are doing work on it.<br />You use a force that is working against the force of gravity.<br />So, when you lift an object, you transfer energy to it and give it gravitational potential energy.<br />
9. 9. Potential Energy<br />Section 1 What is Energy?<br />Chapter 19<br />
10. 10. Section 1 What is Energy?<br />Chapter 19<br />Potential Energy, continued<br />Books on a shelf have gravitational potential energy.<br />The amount of gravitational potential energy an object has depends on its weight and height.<br />Higher and heavier objects have greater gravitational potential energy.<br />
11. 11. Section 1 What is Energy?<br />Chapter 19<br />Mechanical Energy<br />Mechanical energy is the total energy of the motion and position of an object.<br />Both potential and kinetic energy are types of mechanical energy.<br />Mechanical energy can be made up of only potential energy, only kinetic energy, or some of each.<br />
12. 12. Section 1 What is Energy?<br />Chapter 19<br />Other Forms of Energy<br />All matter is made of particles that are always in random motion.<br />Thermal energy is all of the kinetic energy due to the random motion of particles that make up an object.<br />Thermal energy is often measured by measuring temperature.<br />
13. 13. Section 1 What is Energy?<br />Chapter 19<br />Other Forms of Energy, continued<br />All matter also has chemical energy.<br />Chemical energy is energy stored in chemical bonds. It is a form of potential energy.<br />The energy in food is stored as chemical energy.<br />
14. 14. Section 1 What is Energy?<br />Chapter 19<br />Other Forms of Energy, continued<br />Electrical energy is the energy of moving electrons.<br />Sound energy is energy created by an object’s vibrations.<br />In an amplifier, a vibrating cone causes air particles to vibrate. These vibrating particles transmit sound energy to your ear.<br />
15. 15. Section 1 What is Energy?<br />Chapter 19<br />Other Forms of Energy, continued<br />Light energy travels in waves called electromagnetic waves.<br />Electromagnetic waves can be produced by the vibration of electrically charged particles.<br />Some light energy can be seen. Other kinds, such as microwaves and ultraviolet light, can’t be seen by the human eye.<br />
16. 16. Section 1 What is Energy?<br />Chapter 19<br />Other Forms of Energy, continued<br />Nuclear energy is the energy that comes from changes in the nucleus of an atom.<br />The sun’s light and heat come from fusion reactions, when hydrogen nuclei join to make a helium nucleus.<br />Without nuclear energy from the sun, life would not exist on Earth.<br />