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ENERGY

ENERGY. Energy. Energy- the ability to do work SI unit: Joules. Mechanical Energy. Mechanical Energy- Energy do to the position or movement of an object For example, a rollercoaster has mechanical energy in the form of both potential and kinetic energy. Explain.

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ENERGY

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  1. ENERGY

  2. Energy • Energy- the ability to do work • SI unit: Joules

  3. Mechanical Energy • Mechanical Energy- Energy do to the position or movement of an object • For example, a rollercoaster has mechanical energy in the form of both potential and kinetic energy. Explain. http://www.classzone.com/books/ml_science_share/vis_sim/mfm05_pg126_coaster/mfm05_pg126_coaster.html

  4. Potential Energy • Stored Energy / energy of position • amount depends on position or condition of the object

  5. Gravitational Potential Energy • Gravitational Potential energy is greater when the object’s height is greater • G. PE is greater when the object’s weight is greater

  6. Which has more PE, a plant sitting on a 5th floor window or one sitting on a 1st floor window? Why?

  7. PE formula • PE= mass x 9.8 x height • Units • Mass= grams • Height=meters

  8. Example PE Problem • Mass= 65 kg • Height= 35 m • Gravity accel= 9.8 • PE= ? • PE= 65 x 9.8 x 35 • = 22295 Joules

  9. PE word problem • Calc. PE • 1200 kg car at the top of a hill that is 42 m high • M= 1200 • 9.8 • h= 42 • 1200 x 9.8 x 42 = 493920 Joules

  10. Kinetic Energy • “Energy in Motion” • Will change more due to velocity (bc its squared) than mass

  11. Kinetic energy • KE is greater when the speed is greater. • KE is greater when the mass of the object is greater. • Which is more kinetic energy a motorcycle going 35mph or an 18 wheeler going 35 mph? Why?

  12. Kinetic Energy Formula • KE= ½ mass x velocity2

  13. Kinetic Energy Ex Problem • Mass= 44 kg • Speed= 31 m/s • KE= ? • KE= ½ mass x velocity2 • 22 x 961= 21142 Joules

  14. KE Word Problem • Calc KE of 1500 kg car that is moving at a speed of 700m/s • KE= ½ mass x velocity2 • 750 x 490000 = 367500000Joules

  15. From PE to KE

  16. Conservation of Energy • “Energy cannot be created or destroyed” • changes forms • The total amount of energy NEVER changes

  17. More Forms of Energy • Chemical Energy- has to do with ions, atoms, molecules, and bonds • Change to another form of energy when a chemical reaction occurs • Food, Wood, Gasoline, Heating oil • Electrical Energy- associated with voltage and current

  18. More Forms of Energy • Thermal Energy- associated with the movement of molecules • More Motion = More Heat

  19. Sound Energy- associated with longitudinal mechanical waves

  20. Light Energy- associates with electromagnetic waves • Light, X-rays, Lasers, Gamma Rays

  21. Nuclear Energy • Energy associated with Fission and Fusion • Sun and Stars • Occurs only in controlled situations on earth

  22. Energy Transformations • According the Law of Conservation of Energy… • Energy can change forms • Energy in battery then a light turns on • Potential or chemical to electrical

  23. More Energy Transformations • Plant sitting in the sun, then making food then growing • Light energy to chemical energy to kinetic energy • Making music playing the piano • Potential to kinetic to sound

  24. Energy Conversions

  25. Which of the seven main forms of energy is present in each situation?

  26. Work • Work= the force exerted over a distance • When work is done, energy is transferred to the object • If no movement, Zero work!

  27. When force is applied to an object and it moves, work is done, and kinetic energy is created • The greater the force, the greater the kinetic energy of the object

  28. If work is done and an object is lifted, the object gains PE • The higher it is lifted, the more PE

  29. Work Triangle • Calculating Work: • Work= Force x Distance • SI Unit: Joules (J) = 1 Newton*Meter W D F

  30. Example Work Problem • F= 30 N • d= 1.5m • W= ? W= F *d 30 * 1.5 = 45 W= 45 J W D F

  31. Example Work Problem • A carpenter lifts a 45 N beam 1.2 m high. How much work is done on the beam? • F= 45 N • D= 1.2 m • W= ? W= F * D 45 * 1.2 = 54 W= 54 J W D F

  32. Multiple Step • A dancer lifts a 45 kg ballerina overhead a distance of 1.4 m. How much work is done? • F= ? • D= 1.4m • W= ? W= F * d 441 * 1.4 = 617.4 J W= 617.4 J 45 * 9.8= 441 N W D F

  33. Last one • The same dancer holds the ballerina overhead for 5 seconds. How much work is being done? None, no distance is being traveled.

  34. Power • The rate at which work is done • SI unit: Watts (w) = 1 Joule per second • Formula= Power = Work / Time W P T

  35. Example Problem: • W= 500 J • T= 20 s • P= ? P= W / T 500 / 20 = 25 P= 25 watts W P T

  36. Example Problem # 2 • F= 450 N • d= 1.0 m • t= 3 s • W= ? • P = ? W= F * d 450 * 1 = 450 W= 450 J P = W / t 450 / 3 = 150 watts P = 150 watts W P T

  37. Word Problem • A mover carries a chair up the stairs in 30 seconds. His work totals 300 Joules. What was his power? P = w / t 300 / 30 = 10 P= 10 watts W P T

  38. Last one • Mary runs up the stairs in 22 seconds. Carrie runs up the stairs in 27 seconds. Each girl has a work total of 240 Joules. Which has more power? Carrie W= 240 T= 27 240 / 27 = 8.89 P= 8.89 watts Mary W= 240 T= 22 240 / 22= 10.91 P= 10.91 Watts

  39. Machines • change the force that you exert in either size or direction. • Simple Machine- one movement • Compound Machine- more than one movement

  40. Machines at work • 2 forces involved with machines • Input Force (In) – force applied to the machine • Output Force (Out)- force applied by the machine to overcome resistance

  41. Machines at Work • Mechanical Advantage- # of times the machine multiplies input force • MA= input force / output force • MA= input / output Out MA In

  42. Example Problem • Output = 500 N • Input= 20 N • MA= ? • MA= Output / Input 500 / 20 = 25 MA= 25 Out MA In

  43. Another example • Output = 2000 N • Input= ? • MA= 10 • MA= Output/ Input Input= Output / MA 2000 / 10 = 200 N Input= 200 N Out MA In

  44. Word Problem • The power steering in an car has a mechanical advantage of 75. If the input force to turn the steering wheel is 49 N, what is the output force of the car’s front wheels? Output= 3675 N MA= 75 Input= 49 N Output= ? Output= MA * Input 75 * 49 = 3675 N Out MA In

  45. 2 families of Simple Machines • Levers • Inclined planes

  46. Simple Machines • Lever- arm that turns around a fixed point • FULCRUM- fixed part

  47. Types of Levers • 1st Class • 2nd Class • 3rd Class • classified on location Input force, Output force, and fulcrum

  48. First Class Lever • Fulcrum between Input force and Output force • Can multiple force or distance • Ex: Scissors, pliers, clothes pin

  49. 2nd Class Lever • Output between Input force and fulcrum • Multiply force • Examples: Wheel Barrel

  50. 3rd Class lever • Input force between Output force and fulcrum • Increase distance • Examples: bicep, fishing rod, hockey stick

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