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Uses of Energy

Uses of Energy. Energy, Work, Power, Climate. We like to convert E to do work. Conservation of E says we cannot create E, but we can transfer E between objects. E can be transferred by inputting thermal E to object. Fuels release Thermal Energy.

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Uses of Energy

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  1. Uses of Energy

  2. Energy, Work, Power, Climate • We like to convert E to do work. • Conservation of E says we cannot create E, but we can transfer E between objects. • E can be transferred by inputting thermal E to object.

  3. Fuels release Thermal Energy We can use released heat from fuels to transform to other types of E we use to do work. Turn a piston or a turbine.

  4. A Cyclic Process needed to do continuous work. • Engines convert fuel to KE. • In order to have continuous work, system must be returned to original state. • E is “lost” when system returns to original state.

  5. Hamper ex: hot air balloon rises to force rope to rotate a spool thus doing work. Once rope is used up, balloon must cool to return to ground & be re-heated a cycle. Some heat is “lost” in the process when balloon cools to return to ground.

  6. Steam turns a turbine. Convert Heat > KE > Electric + Heat

  7. Electric CurrentChem E (battery) > KE e- > Light (lamp) + Heat

  8. Most processes involve significant E lost to (unwanted) heat.Degraded E.Flashlight battery puts out 100 units, only 10 units transferred to light the rest is degraded “lost” to heat.

  9. Sankey Diagrams show E transfer.Straight arrow shows % useful work.Curved shows % degraded work. Coal Fired Plant Branch width = proportion. input Straight branch useful.

  10. Sankey Diagrams – some more specific about heat losses.

  11. Ex 1: In a car engine chemical E is converted to KE of the wheels as shown. • a. Calculate the overall efficiency of the engine. • b. Calculate the engine efficiency ignoring frictional losses.

  12. Eff = useful work x 100 %tot work • a. 300 J/ 1000 J x 100% = 30% • ~ 550 J “lost” to friction. • b. (300 + 550) J /1000 J x 100% = 85 %

  13. We like to convert E to electricity. • Need some fuel to get a turbine spinning.

  14. Power Plant Heat/ Steam Coils Magnets Electric Fuel source: Coal, Gas, Oil Nukes. Recycle water

  15. List some energy that depend on the sun. • Coal • Oil • Wood • Solar • Wind

  16. List some energy not from the sun. • Tidal • Nuclear • geothermal

  17. Energy Density • Fuels rated by density • The amount of energy per kg fuel. • Oil much denser than wood.

  18. Ex 2. Use the Energy density table Hamper to calculate the following:A steam engine has 4500 kW of power. If we wish to run the engine for 5 hours, how many kg of each type of fuel will be needed? Wood = 4765 kg Coal = 2492 kgOil= 1727 kg

  19. Energy Density 235U = 9 x 107 MJ/kg

  20. Hwk Nuclear Power wksht w/reading.

  21. Power Plants 5:30 min http://www.youtube.com/watch?v=20Vb6hlLQSg&feature=endscreen&NR=1

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