Chapter 4: Energy

1. 9th Grade Physical Science Chapter 4: Energy Sec 4.1: The Nature of Energy Sec 4.2: Conservation of Energy

2. The Nature of Energy 4.1 What is energy? Energy is the ability to cause change. There are many different forms of energy including: light, sound, heat, chemical, nuclear, electrical, potential, and kinetic energy

3. ENERGY OF MOTION! • Energy that appears in the form of motion is called kinetic energy. • The amount of kinetic energy a moving object has depends on the mass of the object and its velocity. • The unit of energy is the joule(pronounced jewel), named after James Prescott Joule, an English scientist. KE = ½ mv2

4. The Nature of Energy 4.1 Potential Energy • Even motionless objects can have energy. Energy is stored in the object. • A hanging apple in a tree has stored energy.

5. The Nature of Energy 4.1 Gravitational Potential Energy • Gravitational potential energy (GPE) is energy stored by objects due to their position above Earth’s surface. • On Earth the acceleration of gravity is 9.8 m/s2, and has the symbol g.

6. The Nature of Energy 4.1 Elastic Potential Energy • If you stretch a rubber band and let it go, it sails across the room. • As it flies through the air, it has kinetic energy due to its motion. • Elastic potential energy is energy stored by something that can stretch or compress, such as a rubber band or spring.

7. mechanical energy = potential energy + kinetic energy Mechanical energy is the total amount of potential and kinetic energy in a system. 4.2

8. Conservation of Energy 4.2 The Law of Conservation of Energy • Energy can change from one form to another, but the total amount of energy never changes. • The law of conservationof energy states that energy cannot be created or destroyed. The total amount of energy in the universe is constant.

9. Potential Energy&Kinetic Energyare both forms ofMechanical Energy Potential Energy Mechanical Energy is not lost Kinetic Energy

10. Conservation of Energy 4.2 Energy Transformations in Projectile Motion • The mechanical energy of the ball remains constant from the time it’s hit until it lands.

11. Section Check 4.1 Question 1 Energy is the ability to cause __________. A! A.) change B.) heat C.) motion D.) work Energy causes change.

12. Section Check 4.1 Question 2 What are the two types of energy we’re studying? Answer We’re studying: kinetic and potential (elastic, chemical, gravitational) k p

13. Section Check 4.1 Question 3 The kinetic energy of an object depends on __________. A.) the object’s speed B.) the object’s mass C.) the object’s mass and speed D.) the acceleration of the object KE = ½ mv2

15. Conservation of Energy 4.2 Conserving Resources • You might have heard about energy conservation or been asked to conserve energy. • These ideas are related to reducing the demand for electricity and gasoline, which lowers the consumption of energy resources such as coal and fuel oil.

16. Conservation of Energy 4.2 Is energy always conserved? • While coasting along a flat road on a bicycle, you know that you will eventually stop if you don’t pedal. • If energy is conserved, why wouldn’t your kinetic energy stay constant so that you would coast forever?

17. Conservation of Energy 4.2 The Effect of Friction • You know from experience that if you don’t continue to pump a swing or be pushed by somebody else, your arcs will become lower and you eventually will stop swinging.

18. The Effect of Friction Friction and air resistance cause some of the mechanical energy of the swing to change to thermal energy. 4.2

19. Conservation of Energy 4.2 Converting Mass into Energy The Sun (and other stars) run by nuclear fusion. During this process a small amount of mass is transformed into a tremendous amount of energy.(more than fission) We do not currently have the technology to create energy with fusion.

20. Conservation of Energy 4.2 Nuclear Fission Nuclear fission produces huge amounts of energy while splitting atoms apart. This is the technology used in atomic bombs.

21. Conservation of Energy 4.2 The Human BodyBalancing the Energy Equation • What forms of energy can you find in the human body? • With your right hand, reach up and feel your left shoulder. • With that simple action, stored potential energy within your body was converted to the kinetic energy of your moving arm.

22. Conservation of Energy 4.2 The Human BodyBalancing the Energy Equation • Much of the chemical potential energy stored in your body is used to maintain a nearly constant internal temperature. • A portion of this energy also is converted to the excess heat that your body gives off to its surroundings.

23. Conservation of Energy 4.2 Energy Conversions in Your Body • Your body stores energy in the form of fat and other chemical compounds. • This chemical potential energy is used to fuel the processes that keep you alive, such as making your heart beat and digesting the food you eat.

24. Conservation of Energy 4.2 Food Energy • The food Calorie (C) is a unit used to measure how much energy you get from various foods1 C is equivalent to about 4,184 J. • Every gram of fat a person consumes can supply 9 C of energy. • Carbohydrates and proteins each supply about 4 C of energy per gram.

25. Section Check 4.2 Question 1 Mechanical energy is the total amount of _________ in a system. A.) potential and kinetic B.) momentum C.) potential energy D.) kinetic energy mechanical energy = KE + GPE

26. Section Check 4.2 Question 2 State the law of conservation of energy. Answer The law of conservation of energy states that energy cannot be created or destroyed.

27. Section Check 4.2 Question 3 mechanical Friction converts __________ energy into ___________ energy. thermal A.) electrical, thermal B.) mechanical, thermal C.) thermal, electrical D.) thermal, mechanical