Ch 8 – Work, Power, & Energy

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# Ch 8 – Work, Power, & Energy

## Ch 8 – Work, Power, & Energy

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##### Presentation Transcript

1. Ch 8 – Work, Power, & Energy “Power” Feb. 11th & 12th, 2014

2. We are going to review… The Do Now/Exit Slip CHART from last class. Add any necessary comments / corrections to the last column! Ask any questions you have!

3. IS IT WORK? A teacher applies a force to a wall and becomes exhausted. Show me your answer (hands up) YES NO NOT QUITE SURE…& that’s OK!

4. IS IT WORK? A teacher applies a force to a wall and becomes exhausted. No. This is not an example of work. The wall is not displaced. A force must cause a displacement in order for work to be done.

5. IS IT WORK? A book falls off a table and free falls to the ground. Show me your answer (hands up) YES NO NOT QUITE SURE…& that’s OK!

6. IS IT WORK? A book falls off a table and free falls to the ground. Yes. This is an example of work. There is a force (gravity) which acts on the book which causes it to be displaced in a downward direction (i.e., "fall").

7. IS IT WORK? A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed. Show me your answer (hands up) YES NO NOT QUITE SURE…& that’s OK!

8. IS IT WORK? A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed. No. This is not an example of work. There is a force (the waiter pushes up on the tray) and there is a displacement (the tray is moved horizontally across the room). Yet the force does not cause the displacement. To cause a displacement, there must be a component of force in the direction of the displacement.

9. IS IT WORK? A rocket accelerates through space. Show me your answer (hands up) YES NO NOT QUITE SURE…& that’s OK!

10. IS IT WORK? A rocket accelerates through space. Yes. This is an example of work. There is a force (the expelled gases push on the rocket) which causes the rocket to be displaced through space.

11. IS IT WORK? Bruno Mars sings during the halftime show Show me your answer (hands up) YES NO NOT QUITE SURE…& that’s OK!

12. IS IT WORK? Bruno Mars sings during the halftime show Depends on your EXPLANATION! Nothing mentioned about him MOVING, so it could be no… Or, you spin it so that his vocal cords are doing work, or his jaw muscles… All depends on your comments!

13. I want to survey your thoughts… On TODAY’S Do Now

14. I want to survey your thoughts… Scenario 1 Scenario 2 Same in Both Fist – not quite sure

15. I want to survey your thoughts… Scenario 1 Scenario 2 Same in Both Fist – not quite sure

16. I want to survey your thoughts… Scenario 1 Scenario 2 Same in Both Fist – not quite sure

17. Let’s take a closer look at #1… • Work is the product of the force and the distance, provided they both act in the same direction. • When a person runs up stairs… • the force lifted is the person’s weight (Newton's), • and the distanceis the verticaldistancemoved (height in meters) – not the distance along the stairs.

18. I want to survey your thoughts… WORK is Force x Distance Is your WEIGHT any different in either scenario? So, is the FORCE you are lifting any different? And you’re doing work against gravity…in what direction does gravity act? So, you’re doing work AGAINST gravity by moving UP…is the vertical distance you move any different in either scenario? SAME WORK IN BOTH… today’s class focuses on why, however, you are more tired if you run up the stairs.

19. Using the info in the boxes, complete #1-2 …may work with the people around you

20. Volunteers to share? How fast work is completed Work divided by time How quickly work can be completed

21. Volunteers to share? P = W t Units = Joule second Power = Work Time Watt = Joule second

22. Volunteers to share? TheyWORK over TIME!!! WATT does a POWERFUL businessperson do? P = W t Watt = Joule second Power = Work Time Corny Joke Memory Aid!

23. James Watt Watt’s improvements to the steam engine were a significant factor in the Industrial Revolution, and when the Watt engine was paired with Thomas Edison’s electrical generator in the late 19th century, the generation of electricity on a large scale was possible for the first time. Retrieved from http://www.magnet.fsu.edu/education/tutorials/pioneers/watt.html

24. Watt coined the term “horsepower” Watt didn’t invent the steam engine, but he did make HUGE improvements on it, which provided a reason to compare the output of horses with that of the engines that could replace them…how else would companies be able to market and sell them? It also was used in selling the “horseless carriage.” Retrieved from www.Christopherwink.com

25. Watt coined the term “horsepower” • A now-famous ‘horseless carriage’ producer was Henry Ford. • Ford sold his first Quadricycle for \$200 in 1896 • He later built two more: one in 1899, and another in 1901. • This machine maxxed out at 20 mph and had a whopping 4 hp • Seen as a toy for the rich • Over 90% of American families made less than \$750/year, & the majority of them earned less than \$500/year Retrieved from Wikipedia and Herndon, Ford: An Unconventional Biography of the Men and Their Times, (New York: Weybright & Talley, 1969), p. 62; also Flammang et al., Ford Chronicle, (Publications International, 1992), p.9 (as cited in Brinkley, David, Wheels for the World: Henry Ford, His Company, and a Century of Progress, (New York: Penguin Group, 2003), p.23 http://digitalgallery.nypl.org/nypldigital/dgkeysearchdetail.cfm?trg=1&strucID=547003&imageID=1219137&word=Wages&s=3&notword&d&c&f=2&k=0&lWord&lField&sScope&sLevel&sLabel&total=3&num=0&imgs=20&pNum&pos=3

26. Still a  toy for the rich …2013 BUGATTI VEYRON 16.4 GRAND SPORT VITESSE Image: fanpop.com Info: motortrend.com

27. Human Horsepower • A healthy human can produce about… • 1.2 hp briefly • and sustain about 0.1 hp indefinitely • Trained athletes can manage up to about … • 2.5 hp briefly • and 0.3 hp for a period of several hours. Retrieved from Eugene A. Avallone et. al, (ed), Marks' Standard Handbook for Mechanical Engineers 11th Edition , Mc-Graw Hill, New York 2007ISBN 0-07-142867-4 page 9-4

28. James Watt + Thomas Edison = 1760 – 1820s: NYC lit by oil lamps Gas street lighting replaced oil lamps in the 1820s, starting at Broadway and Grand Street. 1880: the first electric street lights arrived along Broadway between 14th and 26th Streets—as seen below in this sketch from the April 1881 cover ofScientific American. Retrieved from http://ephemeralnewyork.wordpress.com/2012/09/17/the-first-electric-street-lights-to-illuminate-the-city/

29. James Watt By the early 1900s, this was a bird's eye view of NYC: Retrieved from http://ephemeralnewyork.wordpress.com/2012/09/17/the-first-electric-street-lights-to-illuminate-the-city/

30. And here’s Times Square (early 1900s)… Retrieved from http://www.businessinsider.com/history-of-new-york-famous-nyc-locations-in-pictures-2011-11?op=1

31. And yet despite all this… 1.6 billion people — a quarter of humanity — live without electricity… Breaking that down further: Retrieved from http://www.globalissues.org/article/26/poverty-facts-and-stats

32. So, later in this unit… You will complete a project in which you will explore the pros & cons of your choice of alternative energy sources (non – fossil fuels). One of the areas you will research will involve the feasibility of the energy source to be implemented worldwide.

33. Check in when done; if you can correctly defend your responses, you will be declared an “expert” Mrs. Correia or a student expert can declare other students “experts.” Within 5 minutes, all students should be “experts.”

34. Muscle Up Lab SAFETY Do not overexert yourself. If you feel yourself getting tired, dizzy, or otherwise unwell, stop and immediately see the teacher. Do not do anything to endanger yourself or others. Use a classmate’s data if any of the above apply. See a teacher if you are wearing open toed shoes, as you may not be able to complete some/all of the activities.

35. Muscle Up Lab PROBLEM How can I determine the power used by various muscles in the human body? How can I determine who might be “more powerful” in a certain situation? If something is more ‘difficult,’ does it always require more WORK? If something is more ‘difficult,’ does it always require more POWER?

36. Muscle Up Lab - DISCUSSION Power is usually associated with mechanical advantage or electric motors. Many other devices also consume power or make light or heat. A lighted incandescent bulb may dissipate 100 watts of power. The human body also dissipates power as it converts the energy of food to heat and work. The human body is subject to the same laws of physics that govern mechanical and electrical devices.

37. Muscle Up Lab - DISCUSSION The different muscle groups of the body are capable of producing forces that can act through distances. Work is the product of the force and the distance, provided they both act in the same direction.

38. Muscle Up Lab - DISCUSSION • When a person runs up stairs… • the force lifted is the person’s weight (Newton's), • and the distanceis the verticaldistancemoved (height in meters) – not the distance along the stairs. • When a person jumps, • the force lifted is the person’s weight, • and the distance is the vertical distance jumped • When a person jumps, • the force lifted is the person’s weight, • and the distance is the vertical distance pushed up • If the time it takes to do work is measured, the power output of the body, which is the work divided by the time, can be determined in watts.

39. Muscle Up Lab - PROCEDURE • Select 3 different activities from the list below, or feel free to make your own. If you make your own, please seek teacher approval prior to beginning lab. (*May do more if time permits) • Possible Activities • *Lift a mass with your wrist only, forearm only, arm only, foot only or leg only • **Do push-ups, sit-ups or some other exercise • **Run up stairs (Get a pass!!!) • *Pull a mass with a rope • * **Jump with or without weights attached • Create your own – just be sure to check in with a teacher first! • *You must USE D.A. to convert the mass TO NEWTONS • **You must USE D.A. to convert your weight TO NEWTONS

40. Muscle Up Lab- ANALYSIS • Perform these activities for an amount of time determined by YOU! (10 s, 100 s, 60 s, etc.) • I recommend that one person in the group perform all 3 activities. • Record all info in Data Table A. • In order to determine WORK, you must multiply the distance by the force. In this case, you must also take into account the number of reps. So, the total workdone would be equal to: Force x distance x # of reps

41. Muscle Up Lab- ANALYSIS • Use full sentences & cite data from your lab to answer all 7 analysis questions – see rubric • You will have time next class to complete

42. Muscle Up Lab SUPPLIES • Each lab bench has a supply box, containing: • 4 Role Cards • ONE (1) 500 g mass • ONE (1) 1000 g mass • ONE (1) 500 cm measuring stick • Determine your roles, read all instructions, and begin!

43. Exit Slip • See the BACK of your Do Now for your Exit Slip • Use COMPLETE THOUGHTS • Turn in when done • Don’t forget to do your HW tonight 