Work, Power, and Machines: Physics Lesson Agenda

1. Agenda: 4/29 • Grab a sheet from the basket • Today’s Order of Operations: • Find Someone Who • Test corrections • Work, Power, and Machines Notes • Bingo! • QUESTION: Does anyone have 2.5 or 5 lb weights at home that we can borrow for a lab?

2. Ch. 14, 15, 16 Work, Power, Machines, Energy, and Heat

3. Ch 14 WORK AND POWER • Work – transfer of energy through motion • a. Force must be exerted through a distance

4. Work d F • b. Amount of Work depends on: • 1. Amount of applied Force • 2. Distance over which the force is applied

5. Work d F • c. W=Fd (Force multiplied by distance) • d. Unit is the Joule (1J = 1Nm)

6. e. In order for work to be done: • 1. Something has to move • 2. Motion must be in the direction of the force

7. How much work is done when a car is pushed with 600 N of force for a distance of 50m?

8. How far will a ball roll if 17J of work was done to push it with 2 N of force?

9. Power – rate of doing work a. To increase Power: • 1. increase work done • 2. do work in less time

10. Work t P b. P=W/t • (Work divided by time) c. SI unit is Watt (1W=1J/s) d. Another common unit is horsepower (1hp=746W)

11. How much power is needed to do 40 Joules of work in 5 seconds?

12. How long will it take to generate 70 Watts of power if I do 4900 Joules of work? • How much power will I need if I want to do the same amount of work in half the time? • Twice as much

13. Work Work Fd d t t F P P Reference table check

14. Machines • Make work easier • Device that changes a force

15. How do machines make work easier? • Increasing force • Rising a car using a jack • Increasing distance • Using oars to row a boat • Changing direction • Pulling back on the oars to row a boat More details later-this is an overview :o)

16. Agenda: 5/7 • Trade cell phone for calculator • Get out your Work, Power, and Machines Notes • Be in your seat and ready to start when the bell rings! • Today’s Order of Operations: • Finish Work, Power, and Machines Notes • Work, Power, and Machines Choice Project

17. Work Input (on) vs Work Output (by) • Work done on a machine as the input force acts through the input distance • Work done by a machine as the output force acts through the output distance You cannot get more work out of a machine than you put into it!

18. Mechanical advantage • # of times the machine increases an input force • Actual (AMA) =output force( FR) input force (FE) • FR = resistance (output) force • FE = effort (input) force

19. You test a machine and find it exerts a force of 5N for each 1N of force you exert operating the machine. What is the Actual Mechanical Advantage of the machine? 5N/1N = 5

20. Ideal (IMA) = Mechanical Advantage in absence of friction • IMA =input distance( dE) Output distance (dR) • dE = effort (input) distance • dR = resistance (output) distance • b/c friction is always present, AMA is always less (<) than IMA

21. If x = 3 cm and y = 15 cm, what is the ideal mechanical advantage of the pliers? x y • 15cm / 3cm = 5

22. Efficiency no machine can be 100% efficient, why not? work output Efficiency = ------------------------- X 100% work input

23. Thanks Cambridge Physics Outlet for amazing graphics!

24. You have just designed a machine that uses 1000J of work from a motor for 800J of useful work the machine supplies. What is the efficiency of your machine? 800J / 1000J X 100 = 80%

25. Types of simple machines • Lever – rigid bar that is free to move around a fixed point

26. Fulcrum=the fixed point the bar rotates around • Input arm (effort) = distance between the input force and fulcrum • Output arm (load) = distance between the output force and the fulcrum

27. Position of fulcrum identifies class of lever

28. First class levers • Fulcrum located between the input force (effort) and output force (load) "Give me one firm spot on which to rest (a fulcrum) and I will move the Earth” ~Archimedes

29. Second class levers • Output force (load) is located between the input force (effort) and fulcrum • mechanical advantage is >1 The input distance your hands move to lift the wheelbarrow is larger than the output distance the wheelbarrow moves to lift its load

30. Third class levers • Input force is located between the fulcrum and the output force • Mechanical advantage <1 The output distance over which the lever exerts its force is always larger than the input distance you move the lever through

31. Identify which class lever goes with each picture

32. 2.Wheel and Axle • Variation of a lever • Consists of two disks (cylinders) each one with a different radius

33. 3. Pulley • Variation of a lever • Consists of a rope that is different in size, direction, or both from that of the input force

34. 3 types of pulleys 1. Fixed pulley = changes only the direction of the input force

35. 2. Movable pulley = changes both direction and the size of the input force

36. 3. Pulley System= made up of both fixed & movable pulleys

37. 4. Inclined Plane • Slanted surface along which a force moves an object to a different elevation

38. 5. wedge • Variation of inclined plane • A V-shaped object whose sides are two inclined planes sloped toward each other * A thin wedge has a greater IMA than a thick wedge of the same length

39. 6. Screw • Variation of inclined plane • Wrapped around a cylinder *Screws w/ threads that are closer together have a greater IMA

40. Complex (Compound) Machines • Combination of 2or more simple machines to operate together

41. FYI: Rube Goldberg machine • device, or apparatus is a deliberately over-engineered machine that performs a very simple task in a very complex fashion, usually including a chain reaction. • The expression is named after American cartoonist & inventor Rube Goldberg.

42. IAN page 35: Simple Machines • Define machine. (do this at the TOP of the page under the title) • Define and illustrate each type of simple machine. • Definition from textbook or notes • Illustration should be an appropriate example

43. IAN page 34: Work and Power • Define Work. • Write the equation & circle for Work. • Define all of the variables in the equation & give the units for each. • Define Power. • Write the equation &circle for Power. • Define all variables & give units.

44. You exert a vertical force of 72 N to lift a box a height of 1 meter in a time of 2 seconds. How much power is used to lift the box?

45. Star questions • True or False • Decreasing the amount of time it takes to do work, increases the power • True • Motion must occur in order for work to be done • True

46. Agenda: 5/8 • Trade cell phone for calculator • Be in your seat and ready to start when the bell rings! • Today’s Order of Operations: • PhysiFacts (AMA, IMA, & Efficiency handout) • Work, Power, and Machines Choice Project • Bill Nye Gravity Videot • Reminders: Work, Power, and Machines Choice Project due BY FRIDAY! (it will count as a test grade!)

47. Agenda: 5/9 • Keep cell phones today • You DO NOT need a calculator today • Be in your seat and ready to start when the bell rings! • Today’s Order of Operations: • Gravity Video • Types of Energy IAN page 36 • Work, Power, and Machines Choice Project • Reminders: Work, Power, and Machines Choice Project due BY FRIDAY! (it will count as a test grade!)

48. IAN page 36: Forms of Energy • Define and illustrate each of the forms of energy (there are 6) • Definitions need to come from the textbook • Use pages 450 – 452 in your textbook for definitions and pictures

49. Agenda: 5/10 • Trade cell phone for a calculator • Be in your seat and ready to start when the bell rings! • Today’s Order of Operations: • Energy Notes • Kinetic and Potential Energy IAN page 37 • Survivor Review Game! / Review Sheet

50. NEW SEATS 3rd BLOCK • Group 1: Britney, Skylin, Monseratt, Bryan, Sunnie, Elizabeth • Group 2: Carlos, Tyner, Amber, Krysta, Jayden • Group 3: Colby, Zane, B, Maiyuri, Nia, Jas • Group 4: Jonathan, Yovani, Kinajah, Dulce, Madelyn, Martha • Group 5: Chase, Reagan, Ginger, Dania, Bri