Energy, Work & Power

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Energy, Work & Power

  1. 1. Energy, Work and Power Canadian Academy, Kobedraft presentation under revision staylor@canacad.ac.jp
  2. 2. Energy, Work & Power Unit Question: “How is energy used to produce change?” Areas of interaction: Human ingenuity We design machines to maximise efficiencyCriterion Assessment Tasks
  3. 3. Energy, Work & PowerAssessment Statements • Define energy • Identify the form(s) of energy possessed by an object or system • Distinguish between kinetic and potential energy • Compare the relative quantities of a form of energy possessed by a set of objects. • Define work • Identify how work affects the quantity of energy in an object • Define power • Apply power to the time and work needed to complete a task. • State the SI or commonly-used units for work, energy and power [including Joules (J), Watts (W), Calories, kcal, kiloWatt hours (kWh)] • Define efficiency • Apply efficiency to the energy or power needed to complete a task. • State the principle of conservation of energy • Apply work, power and conservation of energy to discuss energy transfers and transformations in a closed system.
  4. 4. お元気ですか。
  5. 5. お元気ですか。 O-genki desu-ka? “energetic”Energy is the ability to do work. Oh yeah, Grade 10.
  6. 6. Energy is the ability to do work. Unit: joules (J) Many types, including: • Mechanical, Elastic, Gravitational, Kinetic • Chemical, Thermal, Sound, Luminous • Nuclear, Radiant, Magnetic, Electrical • Potential (stored) e.g. gravitational potential e.g chemical potential e.g. elastic potential energyhttp://www.clker.com
  7. 7. Energy is the ability to do work.Potential energy can be converted to kinetic energy e.g. gravitational potential As the cart rolls down the hill, gravitational potential energy is converted to kinetic energy.
  8. 8. Energy is the ability to do work.Unit: joules (J)Many types, including:• Mechanical, Elastic, Gravitational, Kinetic• Chemical, Thermal, Sound, Luminous• Nuclear, Radiant, Magnetic, Electrical• Potential (stored) e.g. gravitational potential The action of a force to cause displacement of an object. Work (J) = force (N) x distance (m) 1 Joule = 1N x 1m
  9. 9. Get up the stairs! Use chemical potential energy to generate mechanical energy to increase your gravitational potential energy!Devise a method to determine how much work is done by each of themembers of your group in getting up the stairs. Consider vertical movementonly for now and the force as their weight. Show your working.Extend your method to calculate the power of eachperson as they ascend the stairs.What variable can they change to be‘more powerful’?What about going downthe stairs?Is running upstairs morework that walking? http://timeandplace.martenhendriks.nl/2008/07/july-21-stairs-drawing-marten-hendriks.html
  10. 10. Who has done the most work? 300kg 500N 500N no movement 100kg 6m 10s 5shttp://www.clker.com/clipart-man-push.html
  11. 11. Who has done the most work? Work = Force x Distance 300kg 500N 500N no movement 100kg 6m 10s 5shttp://www.clker.com/clipart-man-push.html
  12. 12. Who has done the most work? Work = Force x Distance Work = 500N x 0m Work = 500N x 6m = 0J = 3000J (3kJ) 300kg 500N 500N no movement 100kg 6m 10s 5shttp://www.clker.com/clipart-man-push.html
  13. 13. Now who has done the most work? Work = F x d 3600N = _____J (__kJ) 300kg Work = 500N x 6m = 3000J (3kJ) 60s 10m 500N 100kg 6m 5shttp://www.clker.com/clipart-man-push.html
  14. 14. Now who has done the most work? Work = 3600N x 10m 3600N = 36,000J (36kJ) 300kg Work = 500N x 6m = 3000J (3kJ) 60s 10m 500N 100kg 6m 5shttp://www.clker.com/clipart-man-push.html
  15. 15. What is the gain in gravitational potentialenergy of the rock, relative to the ground? 3600N ug = weight x height potential energy due to gravity 300kg 60s 10mhttp://www.clker.com/clipart-man-push.html
  16. 16. What is the gain in gravitational potentialenergy of the rock, relative to the ground? ug = weight x height potential energy due to gravity 300kg = 3000N x 10m = 30,000J (30kJ) 10mhttp://www.clker.com/clipart-man-push.html
  17. 17. Energy storage in a ball Determine the type and magnitude of energy stored in the ball held at 1m height. How much work is being done when you lift the ball as high as you can? How much work is being done when you drop the ball to the ground? Why doesn’t the ball bounce back to the original starting position?
  18. 18. Where did the rest of the energy go? Work = 36,000J (36kJ) ug = 30,000J (30kJ) 3600N 300kg 10mhttp://www.clker.com/clipart-man-push.html
  19. 19. Energy is neither created nor destroyed.It can be transferred from oneobject to another or transformedfrom one form to another.Law of conservation of energy. (The First Law of Thermodynamics)
  20. 20. Where did the rest of the energy go? Work = 36,000J (36kJ) ug = 30,000J (30kJ) 3600N Energy is neither created nor destroyed. 300kg It can be transferred from one object to another or transformed from one form to another. Electrical energy 10mhttp://www.clker.com/clipart-man-push.html
  21. 21. Where did the rest of the energy go? Work = 36,000J (36kJ) ug = 30,000J (30kJ) 3600N Energy is neither created nor destroyed. 300kg It can be transferred from one object to another or transformed from one form to another. Electrical energy Mechanical energy 10m sound energy thermal energy Kinetic energy sound energy thermal energy Gravitational sound energy thermal energy potential energyhttp://www.clker.com/clipart-man-push.html
  22. 22. What energy transfers and transformations are taking place? Energy In Energy Out electrical luminous, sound, radiant, thermal
  23. 23. So… can an object do negative work? When force causes a displacement, work (energy) is positive. When force hinders a displacement, work (energy) is negative. When force results in no displacement, there is no work. Work is not a vector – but Force and displacement are. Pushing the rock Pushing the rock up the Holding the rock up the hill hill – but the rock keeps steady on the hill rolling down d Aargh!
  24. 24. How much work is done by the man? considers only the active force 600N FN 1000N 100kg 50m Ffr Fapplied 200N 600N Fg 200N 1000N
  25. 25. How much work is done by the man? considers only the active force 600N FN 1000N 100kg 50m Ffr Fapplied 200N 600N Fg 200N 1000N Work = 600N x 50m = 30,000J (30kJ)
  26. 26. How much work is done by friction? 600N FN 1000N 100kg 50m Ffr Fapplied 200N 600N Fg 200N 1000N
  27. 27. How much work is done by friction? 600N FN 1000N 100kg 50m Ffr Fapplied 200N 600N Fg 200N 1000N Work = -200N x 50m = - 10,000J (-10kJ)
  28. 28. How much work is done by gravity? 600N FN 1000N 100kg 50m Ffr Fapplied 200N 600N Fg 200N 1000N
  29. 29. How much work is done by gravity? 600N FN 1000N 100kg 50m Ffr Fapplied 200N 600N Fg 200N 1000N Work = 1000N x 0m = 0J (0kJ)
  30. 30. Fail. The crane operator was not using his seatbelt. His mass (before impact) is 80kg. Determine: 1. His ug relative to the ground (before). 2. His ug relative to the rock (before). 300kg 1. The work done by gravity (after). Assume weight = force of gravity. 16m 10mhttp://www.clker.com/clipart-man-push.html
  31. 31. Fail. The crane operator was not using his seatbelt. His mass (before impact) is 80kg. Determine: 1. His ug relative to the ground (before). ug = weight x height = 800N x 16m = 12,800J 2. His ug relative to the rock (before). 300kg 1. The work done by gravity (after). Assume weight = force of gravity. 16m 10mhttp://www.clker.com/clipart-man-push.html
  32. 32. Fail. The crane operator was not using his seatbelt. His mass (before impact) is 80kg. Determine: 1. His ug relative to the ground (before). ug = weight x height = 800N x 16m = 12,800J 2. His ug relative to the rock (before). 300kg ug = 800N x 6m = 4,800J 1. The work done by gravity (after). Assume weight = force of gravity. 16m 10mhttp://www.clker.com/clipart-man-push.html
  33. 33. Fail. The crane operator was not using his seatbelt. His mass (before impact) is 80kg. Determine: 1. His ug relative to the ground (before). ug = weight x height = 800N x 16m = 12,800J 2. His ug relative to the rock (before). 300kg ug = 800N x 6m = 4,800J 1. The work done by gravity (after). Assume weight = force of gravity. Work = F x d = 800N x 16m = 12,800J 16m 10mhttp://www.clker.com/clipart-man-push.html
  34. 34. Energy is the ability to do work. Unit: joules (J) Many types, including: • Mechanical, Elastic, Gravitational, Kinetic • Chemical, Thermal, Sound, Luminous • Nuclear, Radiant, Magnetic, Electrical • Potential (stored) e.g. gravitational potential The action of a force to causeWhen force causes a displacement, work (energy) is positive. displacement of an object.When force hinders a displacement, work (energy) is negative.When force results in no displacement, there is no work. Work (J) = force (N) x distance (m) 1 Joule = 1N x 1m Power is the rate of doing work or using energy. work done (J) energy used (J) Power (W) = = 1 Watt = 1J in 1s time (s) time (s)
  35. 35. Who has the most power?a different guy work done (J) Power (W) = 1 Watt = 1J in 1s time (s) 3600N Crane = 300kg Man = 60s 10m 500N 100kg 6m 5shttp://www.clker.com/clipart-man-push.html
  36. 36. Who has the most power? work done (J) Power (W) = 1 Watt = 1J in 1s time (s) 3600N Crane = 36,000J = 60s 300kg Man = 3000J = 5s 60s 10m 500N 100kg 6m 5shttp://www.clker.com/clipart-man-push.html
  37. 37. Who has the most power? work done (J) Power (W) = 1 Watt = 1J in 1s time (s) 3600N Crane = 36,000J = 600W 60s 300kg Man = 3000J = 600W 5s 60s 10m 500N 100kg 6m 5shttp://www.clker.com/clipart-man-push.html
  38. 38. Quick Quiz: 1. Define energy – what is its unit? 1. Define work – what is its unit? 1. Define power – what is its unit? 1. Name and describe as many forms of energy as you can.
  39. 39. What do you think? Running 1km is harder, so is more work than walking. They are both the same amount of work. Walking takes longer, so is more work.Clipart people from: http://www.clker.com/
  40. 40. Elastic Bands & Bouncy Balls Investigate one factor which my affect the motion of an elastic band or bouncy ball. Resources here: http://goo.gl/XYYB9 “How does ________ affect ______?”Elastic band finger gun from http://www.the-rubber-band.com/hand_shooting.php Bouncy ball: http://goo.gl/B3rYW
  41. 41. Balloon rockets What forms of energy are evident when: • The balloon is inflated? • The balloon is let go? • The balloon has stopped (feel it)? thermal electrical elastic ____ potential kinetic mechanical nuclear magnetic radiant sound luminous Review: • Free body diagram for the balloon. • Free body diagram for the straw. • Reaction force pair for the movement.http://www.education.com/science-fair/article/volume-air-far-balloon-rocket-travels/
  42. 42. Balloon rockets What forms of energy are evident when: • The balloon is inflated? elastic potential • The balloon is let go? kinetic sound elastic • The balloon has stopped (feel it)? thermal Calculate the work done by the balloon. Assume a mean force of 0.5N Calculate the power of the balloon.http://www.education.com/science-fair/article/volume-air-far-balloon-rocket-travels/
  43. 43. Balloon rockets: Blog PostAssessed for Criteria C, B and F. Work in teams to run the rockets and make the videos, butcomplete you own work on the blog post. This is in place of a unit test. Instructions and task-specific clarifications: http://goo.gl/D9lLO Quick notes on annotating YouTube videos: http://goo.gl/azNRc
  44. 44. is the ratio of useful work out from the totalEfficiency amount of work done, as a percentage.* Useful work out (J) Efficiency (%) = x 100 Total work done (J) How is efficiency affected by energy transfers and transformations in the system? How can efficiency of a machine or system be maximised?*http://www.a-levelphysicstutor.com/m-kinetics-power-efficiency.php
  45. 45. What do you think? Ideas based on Concept Cartoons: http://www.conceptcartoons.comClipart people from: http://www.clker.com/search/krug/1

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