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Energy – Chapter 9

Energy – Chapter 9. The Nature of Energy. What is Energy? The ability to do work or cause change Work is the transfer of energy What is Kinetic Energy? Two kinds of energy are POTENTIAL and KINETIC Kinetic is energy of motion Kinetic comes from the Greek word ‘Kinetos’ which means ‘Moving’.

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Energy – Chapter 9

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  1. Energy – Chapter 9 The Nature of Energy

  2. What is Energy? The ability to do work or cause change Work is the transfer of energy What is Kinetic Energy? Two kinds of energy are POTENTIAL and KINETIC Kinetic is energy of motion Kinetic comes from the Greek word ‘Kinetos’ which means ‘Moving’ MAIN IDEA DETAILS 2-Column Notes

  3. Kinetic Energy - Motion Kinetic comes from the Greek word kinetos meaning ‘moving’.

  4. How is Mass and Velocity Related to Kinetic Energy? Kinetic energy depends upon both mass and velocity More mass requires less velocity to have same energy Kinetic energy increases as mass increases Kinetic energy increases as velocity increases 2-Column Notes MAIN IDEA DETAILS

  5. How do we calculate Kinetic Energy? EK = (Mass x Velocity2 )/2 MAIN IDEA DETAILS 2-Column Notes

  6. What is Potential Energy? Potential energy is energy that is stored. It has the potential to do work Energy that has to do with stretching or compressing objects is elastic potential energy Energy that has to do with height is gravitational potential energy MAIN IDEA DETAILS Energy

  7. Calculating Potential Energy • Gravitational Potential Energy = Weight X Height • Weight IS NOT Mass • Weight = Mass X Gravitational Acceleration • SI Unit of measure for weight is ‘newton’. • One ‘newton’ is the force required to accelerate on kg 1 m/s/s • Gravitational Acceleration = 9.8 m/s/s • Energy is measured in ‘joules’ = ‘newton-meter’

  8. (Continued) Gravitational Potential Energy = Weight x Height Energy is measured in joules Weight = Mass x Gravitational Acceleration Therefore: EGP=Mass x Gravity x Height MAIN IDEA DETAILS Energy

  9. What are the different forms of Energy? Mechanical: motion or position of an object Thermal: Total energy in the particles of an object Chemical: Energy stored in chemical bonds Electrical: energy in moving electrons Electromagnetic: energy traveling in waves (light, sound) Nuclear: energy stored in nucleus of an atom MAIN IDEA DETAILS Energy

  10. Kinetic Energy - Motion Kinetic comes from the Greek word kinetos meaning ‘moving’.

  11. Potential Energy – Stored & Waiting The rock has potential to do work, or to move. This is ‘gravitational’ potential energy. Elastic potential energy is associated with objects that can stretch or be compressed (springs). Stored energy has the ‘Potential’ to do work

  12. Mechanical Energy Mechanical Energy is the energy associated with the motion or position of an object.

  13. Thermal Energy - Heat The faster the molecules and electrons move, the more thermal energy it contains. All Atoms and Molecules are particles in motion. The faster they move, the more Thermal energy they have. The more thermal energy, the ‘hotter’ they are.

  14. Chemical Energy – Energy Stored in Chemical Bonds Chemical reactions give off or take in energy to create the chemical bonds. The energy stored in the chemical bonds is Chemical Energy and can be released by breaking the bonds

  15. Electrical Energy Electrical Energy is the energy associated with moving electrical charges.

  16. Electromagnetic Energy - Light Electromagnetic energy is energy traveling in waves. This includes light and sound.

  17. Nuclear Energy Nuclear Energy is the energy that holds the nucleus of an atom together. ‘Splitting’ the nucleus is an atomic reaction that releases tremendous potential energy.

  18. Review Questions • Are energy and work the same thing? • No: Energy is the potential to do work. Work is done when energy is transferred from one object to another • How are kinetic and potential energy different? • Kinetic is the energy of motion. Potential is stored energy.

  19. Review Questions - 2 • List the forms of energy and give an example of each: • Mechanical • Car moving • Thermal: • Warm water • Chemical • Gasoline • Electrical • Battery • Electromagnetic • Light • Nuclear • Sun

  20. Review Questions - 3 • A boulder weighs 200N, poised at the edge of a 100M cliff. What is its gravitational potential energy? Draw a graph of its potential energy as it falls from 100M to 50M to 20M to 10M • EGP=200N x 100M • = 20,000J • At 50 M, = 200N x 50M = 10,000J • At 20 M, = 200N x 20M = 4000J • At 10 M, = 200N x 10M = 2000J

  21. Exercise – calculate your potential energy • One Kg is 2.2 pounds at sea level. • Your mass is your weight divided by 2.2 • Assume you are 1 meter above the floor, about the height of the desk. • The gravitational acceleration constant is 9.8 m/s/s

  22. Energy Conversion and Conservation

  23. How do conversions between forms of energy occur? Change from one form of energy to another is an energy conversion Any form of energy can be converted to any other form MAIN IDEA DETAILS Energy Conversion and Conservation

  24. How Does Kinetic and Potential Energy Convert? Potential to Kinetic and vice versa is most common conversion. What is the energy conversion in juggling? Object rising or falling is changing kinetic energy to/from Gravitational Potential Energy What is the energy conversion in a Waterfall: At top of waterfall, water has potential energy. As it falls it is converted to kinetic energy. MAIN IDEA DETAILS Energy Conversion & Conservation

  25. What is the energy conversion in a Pole Vault? Pole vaulter runs (kinetic). Plants pole which bends (elastic). Vaulter springs into the air (kinetic) which changes to height (gravitational potential). Vaulter falls (kinetic) What is the energy conversion in a pendulum? Continuous conversion between gravitational potential and kinetic. As it goes up, kinetic is converted to potential. Going down, converted from potential to kinetic MAIN IDEA DETAILS Energy Conversion and Conservation

  26. What is the law of conservation of energy? Energy cannot be created or destroyed, but can be transformed to any other type of energy OR- When one form of energy is converted to another, no energy is destroyed in the process MAIN IDEA DETAILS Energy Conversion & Conservation

  27. What is the relationship between energy and matter? Einstein: Energy can be created by destroying matter Nuclear reactions What is Conserving Energy? Not the same as conservation of energy Means saving or not wasting energy MAIN IDEA DETAILS Energy Conversion & Conservation

  28. Reality and Energy Conversions • No energy conversion is 100% efficient • Some energy is always lost to the environment • Usually as heat • Power Generation through Energy Usage is a problem of efficiency • Efficiency = $$$$ • Heat is a form of pollution • Global warming • Kills fish in lakes that are too warm

  29. What is an energy conversion? A change from one form of energy to another form State the law of conservation of energy in your own words: The total energy before a process is the same as the total after the process. MAIN IDEA DETAILS Review Questions

  30. Describe the energy conversions that occur when a ball is dropped and bounces back up. Why do you think the ball bounces a little lower each time? Falling: potential changes to kinetic. Bouncing back up: kinetic changes back to potential Ball does not bounce as high because some energy escapes as thermal (friction) or sound MAIN IDEA DETAILS Review Questions

  31. A roller coaster car with a mass of 500 Kg is at the top of the hill that is 30m high. Without friction, what would its kinetic energy be as it reached the bottom of the hill? Without friction, kinetic would equal gravitational potential: 500kg x 9.8 m/s2 x 30 m = 147,000J MAIN IDEA DETAILS Energy Conversion & Conservation

  32. Energy Conversions

  33. Energy Conversion • Energy transformation, energy transfer, energy conversion or power transfer, • any process of transforming one form of energy into another. • Energy of fossil fuels, solar radiation, or nuclear fuels can be converted into other energy forms such as electrical, propulsive, or heating that are more useful to people. • Often, machines are used to transform energy. • The efficiency of a machine characterizes how well (how efficiently) it can produce a useful output (such as work for example) through such a conversion.

  34. Energy Conversion • Coal Power Plants: • For instance, a coal-fired power plant involves these power transfers: • Potential energy in the coal converted to thermal energy • Thermal energy converted to kinetic energy in steam • Steam energy converted to mechanical energy in the turbine • Mechanical energy of the turbine converted to electrical energy, which is the ultimate output

  35. Energy Conversions - Car • Potential energy in the fuel converted to kinetic energy of expanding gas via combustion • Kinetic energy of expanding gas converted to linear piston movement • Linear piston movement converted to rotary crankshaft movement • Rotary crankshaft movement passed into transmission assembly • Rotary movement passed out of transmission assembly in second step • Rotary movement passed through differential • Rotary movement passed out of differential to drive wheels • Rotary movement of drive wheels converted to linear motion of the vehicle

  36. Other Energy Conversions • Thermophotovoltaics (Heat → Electricity) • Geothermal power (Heat → Electricity) • Heat engines, such as the internal combustion engine used in cars, or the steam engine (Heat → Mechanical energy) • Ocean thermal power (Heat → Electricity) • Hydroelectric dams (Gravitational potential energy → Electricity) • Electric generator (Kinetic energy or Mechanical work → Electricity) • Fuel cells (Chemical energy → Electricity) • Lamp (Chemical energy → Heat and Light) • Microphone (Sound → Electricity) • Nuclear reactor (Nuclear energy → Electricity) • Fossil fuel power plant (Chemical energy → Electricity) • Solar cells (Light → Electricity), including downconversion and upconversion • Solar thermal (Light → Heat) • Wave power (Mechanical energy → Electricity) • Windmills (Wind energy → Electricity or Mechanical energy) • Piezoelectrics (Strain → Electricity) • Acoustoelectrics (Sound → Electricity)

  37. Energy Conversion Efficiency

  38. Energy Conversion Efficiency

  39. How are Fossil Fuels Formed? Stored energy from hundreds of millions of years ago, formed by geologic processes Includes: coal, gas, petroleum Contain energy that came from the sun MAIN IDEA DETAILS Energy Conversion & Fossil Fuels

  40. How do we use fossil fuels? Burned to release the potential chemical energy Chemical changed to thermal (fire) to heat water Water (steam) turns turbines (mechanical) Turbine turns a generator to make electricity MAIN IDEA DETAILS Energy Conversion & Fossil Fuels

  41. How is the chemical energy in fossil fuels related to the sun’s energy? Fossil fuels are stored energy from the sun How is the energy of coal released? Combustion (burned) to release potential energy into thermal energy MAIN IDEA DETAILS Energy Conversion & Fossil Fuels

  42. Describe energy conversions involved in the formation of coal. Nuclear energy (sun) converted to electromagnetic (light) Light converted to chemical (Plants/animals) When exposed to high temperature and pressure over many years, it becomes coal. MAIN IDEA DETAILS Energy Conversion & Fossil Fuels

  43. Make a general statement about the supply of fossil fuels, given what you know about how fossil fuels are formed: Fossil fuels are formed much more slowly than we are using them, so supply may become increasingly scarce. MAIN IDEA DETAILS Energy Conversion & Fossil Fuels

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