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? 1.Pushing on a book forward and the books moves forward. 2.Pulling on a wall and the wall doesn’t move 3.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 stairs 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 & Axle – Lever – Wedge

20. Input force & Output force Input Force – Force applied to the machine – Symbol = F in Output Force – Force applied by the machine – Symbol = F out

21. Input Work & Output Work Input Work – Work done by you on a machine – Symbol = W in Output Work – Work done by the machine – Symbol = W out

22. Input & Output Work: The Relationship Input work equals Output work in an ideal machines W in = W out 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 = F r / F e AMA= actual mechanical advantage F r = resistance force (output force) F e =effort force (input force) AMA has no unit F r & F e 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 = d e / d r IMA = ideal mechanical advantage d e = displacement of effort force (input distance) d r = displacement of resistant force (output distance) IMA has no unit d e and d r 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 W out = work output (J) W in = 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?