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April 15General Science Chapter 61 Machines Chapter 6.

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Presentation on theme: "April 15General Science Chapter 61 Machines Chapter 6."— Presentation transcript:

1 April 15General Science Chapter 61 Machines Chapter 6

2 April 15General Science Chapter 62 Machine A device that makes work easier

3 April 15General Science Chapter 63 Simple machine A device that does work with only one movement There are six types  LeversInclined Plane  PulleyWedge  Wheel & AxleScrew

4 April 15General Science Chapter 64 Work and machines Work is done when a force is exerted through a distance Machines make work easier by changing the size or direction of the force, or both.  Opening a paint can with a screwdriver Changes size – you can use less force Changes direction

5 April 15General Science Chapter 65 Forces and machines Effort force (F e ) – applied to the machine  The force you exert Resistance force (F r ) – applied by the machine to overcome gravity or friction

6 April 15General Science Chapter 66 Work and machines Work input (W in ) – work done on the machine  Effort force times distance it moves  W in = F e X d e Work output (W out ) – work done by the machine  Resistance force times distance it moves  W out = F r X d r

7 April 15General Science Chapter 67 Conservation of energy You can never get more work out than you put in If force increases, distance must decrease.

8 April 15General Science Chapter 68 Mechanical advantage The number of times a machine multiplies the effort force

9 April 15General Science Chapter 69 Mechanical advantage Can be greater than 1  Opening paint can Can be equal to 1  Raising blinds Can be less than 1  Hitting a baseball

10 April 15General Science Chapter 610 Example A worker applies an effort force of 10 N to pry open a window that has a resistance of 500 N. What is the mechanical advantage of the crowbar? F r = 500 NF e = 10 N

11 April 15General Science Chapter 611 You try A jack is used to lift a 2000-N rock. The effort force is 200 N. Find the mechanical advantage.

12 April 15General Science Chapter 612 Discuss #1 A simple machine is a device that does work with only one __________. List the 6 simple machines  Give an example of each What is the force applied to a machine? What is the force applied by a machine?

13 April 15General Science Chapter 613 Discussion #1 What is mechanical advantage? What does it mean when the MA value is equal to 1? How do we calculate MA?

14 April 15General Science Chapter 614 Levers Examples  Crowbars  Seesaws  Baseball bat

15 April 15General Science Chapter 615 Definitions A lever is a bar that is free to pivot, or turn, about a fixed point. A fulcrum is the fixed point of a lever. The effort arm is the part of the lever on which the force is applied. The resistance arm is the part of the lever that exerts the resistance.

16 April 15General Science Chapter 616 Lever fulcrum Resistance arm Effort arm Effort force

17 April 15General Science Chapter 617 Mechanical advantage Review, we learned that We can also use for levers

18 April 15General Science Chapter 618 You try You use a crowbar 160 cm long as a lever to lift a large rock. The rock is 20 cm from the fulcrum. You push down on the other end of the crowbar. What is the length of the effort arm? The resistance arm? What is the MA of the lever?

19 April 15General Science Chapter 619 First class levers The fulcrum is in the middle  Seesaw  crowbar fulcrum Resistance arm Effort arm Effort force

20 April 15General Science Chapter 620 Second class levers The resistance is in the middle  wheelbarrow  nutcracker fulcrum Resistance arm Effort arm Effort force

21 April 15General Science Chapter 621 Third class levers The effort is in the middle  Baseball bat  broom fulcrum Resistance arm Effort arm Effort force

22 April 15General Science Chapter 622 Discuss #2 What is a lever? What is a fulcrum? What is the effort arm? What is the resistance arm?

23 April 15General Science Chapter 623 Discussion #2 What are the 3 types of levers?  What is an example of each type of lever?  Which type usually has a MA value less than 1?

24 April 15General Science Chapter 624 Pulleys Pulley – grooved wheel with a rope or chain running along the groove Acts like a lever  The two ends of the rope are the effort arm and the resistance arm  The wheel acts like the fulcrum

25 April 15General Science Chapter 625 Fixed pulley Attached to something that doesn’t move Change the direction of a force MA of 1 LeLe LrLr FrFr FeFe

26 April 15General Science Chapter 626 Movable pulley Attached to the object being moved MA greater than 1 Effort distance must be greater than resistance distance LeLe LrLr FrFr FeFe

27 April 15General Science Chapter 627 Block and tackle System of fixed and movable pulleys Has MA equal to the number of ropes that support the resistance weight  Count every rope coming off the movable pulleys

28 April 15General Science Chapter 628 Examples of Block & Tackle

29 April 15General Science Chapter 629 Example of Block & Tackle #2

30 April 15General Science Chapter 630 Wheel and axle Consists of two wheels of different sizes that rotate together  The effort force is usually applied to the large wheel  The small wheel, or axle, exerts the resistance force Examples: doorknob, water faucet, gears, pencil sharpener

31 April 15General Science Chapter 631 Wheel and axle Can be thought of as a lever attached to a shaft  Radius of wheel is effort arm  Radius of axle is resistance arm  Center of axle is fulcrum

32 April 15General Science Chapter 632 Inclined plane A ramp Lifting something along an inclined plane means you cover more distance than lifting it straight up, but you get to use a smaller force

33 April 15General Science Chapter 633 Screw An inclined plane wrapped in a spiral around a cylindrical post. As you drive in a screw, the inclined plane slides through the wood.

34 April 15General Science Chapter 634 Wedge An inclined plane with one or two sloping sides Examples  Chisels  Knives  Axe blades The material stays in place while the wedge moves through it.

35 April 15General Science Chapter 635 Variations All six kinds of simple machines are variations of two basic machines  The lever  The inclined plane

36 April 15General Science Chapter 636 Discuss #3 What kind of simple machine is a ramp? What is an inclined plane wrapped in a spiral around a cylindrical post? What kind of simple machine are chisels, knives, and axes?

37 April 15General Science Chapter 637 Discussion #3 What type of pulleys have a MA = 1? What is the difference between a fixed pulley and a movable pulley? What is a block and tackle? What two groups can simple machines be broken into?

38 April 15General Science Chapter 638 Compound Machine A machine that is made up of 2 or more simple machines. Examples of compound machines  Fishing rod, pencil sharpener, an axe

39 April 15General Science Chapter 639 Rube Goldberg #1 Open window (A) and fly kite (B). String (C) lifts small door (D) allowing moths (E) to escape and eat red flannel shirt (F). As weight of shirt becomes less, shoe (G) steps on switch (H) which heats electric iron (I) and burns hole in pants (J). Smoke (K) enters hole in tree (L), smoking out opossum (M) which jumps into basket (N), pulling rope (O) and lifting cage (P), allowing woodpecker (Q) to chew wood from pencil (R), exposing lead. Emergency knife (S) is always handy in case opossum or the woodpecker gets sick and can't work.

40 April 15General Science Chapter 640 Rube Goldberg #2

41 April 15General Science Chapter 641 Rube Goldberg #3 ew/1487 Honda video ew/1487

42 April 15General Science Chapter 642 Efficiency Measure of how much of the work put into a machine is changed to useful work put out by the machine.

43 April 15General Science Chapter 643 Efficiency Can it ever be more than 100%? How can we increase efficiency?

44 April 15General Science Chapter 644 example A worker pushes a 1500 N chair up an inclined plane that is 4.0 m long and 1.0 m high. The worker exerts a force of 500 N. What is the efficiency of the inclined plane? 1 m 4 m

45 April 15General Science Chapter 645 You try Using a fixed pulley, you pull the rope down 1.0 m with a force of 72 N. A 65-N object is raised 1.0 m. What is the efficiency of the pulley?

46 April 15General Science Chapter 646 Power Power is the rate at which work is done.

47 April 15General Science Chapter 647 Watts Power is measured in Watts, named after James Watt, who invented the steam engine. 1 W = 1 J/s Very small unit, so we often use kW Watts = 1 horsepower

48 April 15General Science Chapter 648 Example A figure skater lifts his partner, who weighs 450 N, 1 meter in 3 seconds. How much power is required?

49 April 15General Science Chapter 649 You try A N elevator rises 30.0 m in 60.0 s. How much power is required? Express your answer in kW.

50 April 15General Science Chapter 650 Making Connections Joules = 1 calorie  Joules are units for energy and work 1 Calorie = 1000 calories  A Calorie is used for foods, so if a candy bar has 250 Calories it is the same as calories.

51 April 15General Science Chapter 651 Example #1 Tommy eats a candy bar that has 230 Calories. How many Joules is that? 1 Calorie = 1000 calories 1 calorie = Joules so 1 Cal = 4184 Joules therefore 230 Calories = Joules

52 April 15General Science Chapter 652 Example #1 continued How much Power can be produced with the 230 Calorie candy bar in 1 hour? 230 Cal = Joules Use the equation below

53 April 15General Science Chapter 653 Example #1 continued..

54 April 15General Science Chapter 654 Discuss #4 What is a compound machine? What is efficiency? What part of an axe is the lever?  What class of lever is it?  What are the benefits of attaching a wedge to a lever to make an axe?

55 April 15General Science Chapter 655 Discussion #4 What units are used to measure Power? Why is the unit kW used more often than W? What is the conversion factor for horsepower to Watts?


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