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Chapter 9

Chapter 9. Energy. Section 1: Objectives. Explain the relationship between energy and work. Compare kinetic energy and potential energy. Describe the different forms of energy. Energy and Work. Energy is the ability to do work.

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Chapter 9

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  1. Chapter 9 Energy

  2. Section 1: Objectives • Explain the relationship between energy and work. • Compare kinetic energy and potential energy. • Describe the different forms of energy.

  3. Energy and Work • Energy is the ability to do work. • Work is done when a force causes an object to move in the direction of the force. • Work is a transfer of energy. • Energy and work are expressed in units of joules (J).

  4. Energy and Work • Kinetic energy is the energy of motion. • All moving objects have kinetic energy. • Kinetic Energy Depends on Mass and Speed If you know an object’s mass (m) and its speed (v), you can calculate the object’s kinetic energy with the following equation:

  5. Energy and Work • The formula used to calculate kinetic energy: KE = (mass)(volume)^2 2 Energy is also expressed in Joules. 2

  6. Calculating Kinetic Energy

  7. Example # 1 • What is the KE of a car that has a mass of 2,400 kg and is moving at 20 m/s? Remember: KE = (mass)(volume)^2 2 Energy is expressed in Joules

  8. Example # 2 • A) What is the KE of a 4,000 kg elephant that is running at 2 m/s? • B) What about the same elephant running at 4 m/s?

  9. Example # 3 • A)What is the KE of a 2,000 kg bus that is moving at 30 m/s? • B) What about the same bus moving at 40 m/s?

  10. Energy and Work • Potential energy is the energy an object has because of its position. • Gravitational Potential EnergyThe amount of GPE that an object has depends on its weight and its height.

  11. Energy and Work • The equation to find gravitational potential energy is: • GPE weight  height • Gravitational potential energy is equal to the amount of work done on an object to lift it a certain height.

  12. Calculating GPE

  13. Example # 1 • What is the GPE of a cat that weighs 40 N and is standing on a table 0.8 meters off the ground? • Remember: GPE weight  height • Energy is expressed in Joules.

  14. Example # 2 • What is the GPE of a diver who weighs 500 N and is standing on a platform 10 meters off the ground? • Remember: GPE weight  height • Energy is expressed in Joules.

  15. Example # 3 • What is the GPE of a diver who weighs 600 N and is standing on a platform that is 8 meters off the ground? • Remember: GPE weight  height • Energy is expressed in Joules.

  16. Energy and Work • When you find out an object’s gravitational potential energy, the “ground” that you measure the object’s height from depends on where it is. • The height you use in calculating gravitational potential energy is a measure of how far an object has to fall.

  17. Energy and Work • Mechanical energy is the total energy of motion and position of an object. • Both kinetic energy and potential energy are kinds of mechanical energy. • The equation to find mechanical energy is: • mechanical energy  potential energy  kinetic energy

  18. Energy and Work • The mechanical energy of an object remains the same unless it transfers some energy to another object. • But even if the mechanical energy of an object stays the same, the potential energy or kinetic energy can increase or decrease.

  19. Energy and Work • Thermal Energy is all of the kinetic energy due to random motion of the particles that make up an object. • All matter is made up of particles that are always in random motion. • So, all matter has thermal energy. • Thermal energy increases as temperature increases and increases as the number of particles increases.

  20. Thermal Energy

  21. Energy and Work • Chemical Energy is the energy of a chemical compound that changes as its atoms are rearranged. • Chemical energy is a form of potential energy because it depends on the position and arrangement of the atoms in a compound. • The energy in food is chemical energy.

  22. Energy and Work • Electrical Energy is the energy of moving electrons. • Electrical energy can be thought of as potential energy that is used when you plug in an electrical appliance and use it. • Sound Energy is caused by an object’s vibrations. • The object’s vibrations transmit some kinetic energy to the air particles, which also vibrate. These vibrations transmit sound energy.

  23. Energy and Work • Light Energy is produced by the vibrations of electrically charged particles. • Nuclear Energy is energy that comes from changes in the nucleus of an atom. • Nuclear energy can be produced when nuclei are joined in a fusion reaction or when a nucleus is split apart in a fission reaction.

  24. Chapter 9 Sec. 1 Pop Quiz • 1) What 2 things must happen for work to be done on an object? • 2) T/F All moving objects have kinetic energy. • 3) What is the formula used to calculate KE? • 4) What 2 things does GPE depend on? • 5) What is the formula used to calculate GPE?

  25. Chapter 9 Sec. 1 Pop Quiz • 6) List 2 kinds of mechanical energy. • 7) What is the formula used to calculate mechanical energy? • 8) Describe the particles that make up matter. • 9) Why is chemical energy a form of potential energy? • 10) List 2 ways nuclear energy can be produced.

  26. Section 2: Objectives • Describe an energy conversion. • Give examples of energy conversions for the different forms of energy. • Explain how energy conversions make energy useful. • Explain the role of machines in energy conversions.

  27. Energy Conversions • An energy conversion is a change from one form of energy to another. • Any form of energy can change into any other form of energy. • As the skateboarder on the next slide travels up and down the half-pipe, his energy changes back and forth between kinetic energy and potential energy.

  28. Energy Conversions

  29. Energy Conversions • Elastic Potential EnergyStretching a rubber band stores elastic potential energy in the rubber band. • When you let the rubber band go, it goes back to its original shape. • It releases its stored-up potential energy as it does so.

  30. Energy Conversions • Chemical energy is stored in the food you eat. • Your body uses this chemical energy to function. • Energy Conversion in Plants The chemical energy in the food you eat comes from the sun’s energy. • Plants use photosynthesis to convert light energy into chemical energy.

  31. Energy Conversions

  32. Energy Conversions • Plants change light energy into chemical energy. • The chemical energy in the food you eat is changed into another kind of chemical energy that your body can use. • Your body then uses that energy to give you kinetic energy that you use in everything you do.

  33. Energy Conversions • Energy conversions are needed for everything we do. • Heating our homes, getting energy from a meal, and many other things use energy conversions. • Machines help harness energy and make that energy work for you.

  34. Energy Conversions • Conversions Involving Electrical Energy Some common energy conversions that involve electrical energy are shown in the table below. • Alarm clock • electrical energy  light and sound energy • Battery • chemical energy  electrical energy • Light bulb • electrical energy  light and thermal energy • Blender • electrical energy  kinetic and sound energy

  35. Energy Conversions • A machine can make work easier by changing the size or direction (or both) of the force needed to do the work. • Some machines allow you to use less force over a greater distance to do the same amount of work. • Machines as Energy Converters Some machines help you use energy by converting it into the form of energy that you need.

  36. Energy Conversions

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