Work, Power, and Machines

1. Work, Power, and Machines Physical Science

2. What is Work? • Transfer of Energy • Occurs when a force makes an object move a distance

3. When Is Work Done? • Work Done • Object moves in the direction of the force • No Work Done • No movement • Direction of the force and direction of movement are different

4. Is Work being Done? • Pushing on a book forward and the books moves forward. • Pulling on a wall and the wall doesn’t move • Push on a car forward and it rolls backwards

5. Work Formula • Work = Force * Distance W = F*d • W= work (unit: Joules [J]) • F = force (N) • D = distance (m)

6. Work Example Practice 1. A man weighing 750 N climbs a flight of starts 5-m high. How much work did he do? 2. Kayla does 40 J of work while pushing a shopping cart 30 meters. How much force was applied?

7. Work Example Practice 3. David pulls a 450-N sofa up the stairs producing 25-J of work. How far did he pull the sofa?

8. What is Power? • Is the Rate of Doing Work • To increase power, you can increase the amount of work done in a given time

9. Power Formula • Power = Work ÷ time P = W / t • P = power (unit: Watts [W]) • W = work (J) • t = time (s)

10. Power Example Problems 1. A motorcycle does 2000-J of work in 25 seconds. How much power is produced? 2. Mary produced 20-W of power in 0.5 seconds doing push-ups. How much work was done?

11. Work and Power Formulas Together Beth moves a 15 N walker (zombie) 20 meters in 10 seconds. How much power was produced?

12. End DAY 1

13. What is a Machine? • A device that makes doing work easier • Two divisions • Simple machines • Compound Machines

14. How do Machines make work Easier? • Increase Force • (ex: car jacks) • Increase the distance a force is applied • (ex: using a ramp) • Changing the direction of an applied force • (ex: ax blade)

15. Simple Machines • Machines that does work with only one movement of the machine

16. Six types of Simple Machines 1). Lever A bar that is free to pivot or turn around a fixed point (ex: teeter totter) 2). Pulley Grooved wheel with a rope, chain, or cable running along the groove (ex: wishing well)

17. Six types of Simple Machines 3). Wheel & Axle A shaft/axle attached to the center of a larger wheel so that both rotate together (ex: door knobs) 4). Inclined Plane A sloping surface (ex: ramp)

18. Six types of Simple Machines 5). Screw An inclined plane wrapped in a spiral around a cylindrical post (ex: jar lids) 6). Wedge An inclined plane with one or two sloping sides (ex: knife)

19. What are Compound Machines? • When two or more simple machines operate together • Example: Can Opener • Wheel & Axel • Level • Wedge

20. Input force & Output force • Input Force • Force applied to the machine • Symbol = Fin • Output Force • Force applied by the machine • Symbol = Fout

21. Input Work & Output Work • Input Work • Work done by you on a machine • Symbol = Win • Output Work • Work done by the machine • Symbol = Wout

22. Input & Output Work: The Relationship • Input work equals Output work in an ideal machines • Win = Wout • Why? • Law of conservation of Energy • Energy is not created nor destroyed

23. End DAY 2

24. What is Mechanical Advantage? • Is the number of times that a machine increases an input force • Two Versions • Actual Mechanical Advantage • Ideal Mechanical Advantage

25. Actual Mechanical Advantage • Determined by measuring the actual forces on a machines • Ratio of the output force to the input force

26. Actual Mechanical Advantage Formula AMA = Fr / Fe • AMA= actual mechanical advantage • Fr= resistance force (output force) • Fe=effort force (input force) • AMA has no unit • Fr & Fe has the unit of “N”

27. AMA Formula Practice 1) What is the actual mechanical advantage of a machine who’s input force is 30-N but produces an output force of 90-N? 2) You test a machine and find that it exerts a force of 10 N for each 2 N of force you exert operating the machine. What is the actual mechanical advantage of the machine?

28. Ideal Mechanical Advantage • Is the mechanical advantage in the absence of friction • Because friction is always present, the actual mechanical advantage of a machine is always less than the Ideal

29. Ideal Mechanical Advantage Formula IMA = de / dr • IMA = ideal mechanical advantage • de = displacement of effort force (input distance) • dr = displacement of resistant force (output distance) • IMA has no unit • de and dr has the unit of meters

30. IMA Formula Practice 1) A woman drives a car up onto wheel ramps to perform some repairs. If she drives a distance of 1.8 meters along the ramp to raise the car 0.3 meter, what is the IMA? 2) A construction worker moves a crowbar through a distance of 4 meters to lift a load 0.5 meter off the ground. What is the IMA of the crowbar?

31. What is efficiency? % • The percentage of work input that becomes work output • Because there is always some friction, the efficiency of any machine is always less than 100 percent

32. Efficiency Formula • Wout = work output (J) • Win = work input (J)

33. Efficiency Formula Practice 1) You have just designed a machine that used 1000 J of work from a motor for every 800 J of useful work the machine supplies. What is the efficiency of your machine?