(Are they really that simple?!)

# (Are they really that simple?!)

## (Are they really that simple?!)

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##### Presentation Transcript

1. (Are they really that simple?!)

2. What is work? • In science, the word work has a different meaning than you may be familiar with. • #1 According to your text, work is done when a force causes an object to move in the direction of the force

3. Work or Not? • According to the scientific definition, what is work and what is not? • a teacher lecturing to her class • a mouse pushing a piece of cheese with its nose across the floor

4. Chapter 8 Section1 What is Work?

5. Chapter 8 Section1 What is Work?

6. Chapter 8 Section1 What is Work?

7. Chapter 8 Section1 What is Work?

8. Chapter 8 Section1 What is Work?

9. 2. What is a “force”? • A push or a pull What unit describes the size of a force? • Newton (N) Measured with a spring scale

10. 3. What is a machine? • Something that makes work easier

11. 4. How do machines make work easier? What do machines do? • They change the size or direction of the force you apply

12. 5. The work YOU do on a machine is called the • Work input (input force) OR effort The work done by the machine on another object is called the • Work output (output force) work input or effort work output

13. 6. Machines DO NOT change the amount of work done. They only make it easier. • Work = F (force) X d (distance) 12 J = 3N x 4m 12 J = 2N x 6m 12J = 1N x 12m

14. So, why use machines? Machines make work easier by changing the • amount of force you exert • distance over which you exert your force, or • direction in which you exert your force However, the amount of work does not change! (W=Fxd)

15. TIME OUT!!! What is “mechanical advantage”? • Jot this down at the bottom of your page! Mechanical advantage is the number of times a machine multiplies force. • The greater the MA, the less effort required and the easier the work! • And that’s a GOOD thing! 

16. Inclined plane p. 145Describe: • Flat, slanted surface. An inclined plane makes work easier by letting you apply a _____________ force over a __________________ smaller longer distance The longer the ramp, the less effort required, the greater the mechanical advantage.

17. Inclined Plane: Examples • ramp • stairs • hills • boat ramps • winding roads • slides

18. Which inclined plane has the greater mechanical advantage? Why? See your lab: Exploring Inclined Planes! Which machine above makes less work? Did I getcha? Work is the same; it just gets easier! Why? Shorter distance, more effort. 2m x 6N = 12J Longer distance, less effort. 6m x 2N = 12 J

19. Wedge p. 146Describe: • Two inclined planes that move Like the inclined plane, the wedge needs a __________ input force over a _________________ small large distance

20. Which wedge has the greater mechanical advantage? The longer and thinner, the greater the mechanical advantage. That’s why sharper knives work better for cutting!

21. Wedge: Examples • nails • knives • chisels • axes • paper cutter • can opener • needle/pin • door stop

22. Screw p. 146Describe: • An inclined plane wrapped around a cylinder To turn a screw, a ____________ force over a ______________ is needed. smaller greater distance The closer the threads, the greater the mechanical advantage.

23. Which screw has the greatest mechanical advantage? • Remember to look at the pitch-how close the threads are!

25. Screw: Examples • screws • light bulbs • bolts • jar lids • C-clamps • corkscrews • drill bits

26. 1st class lever p. 141Describe a lever: A bar that rotates at a fixed point Resistance is AKA the load What is a fulcrum? A fixed point What’s in the middle? FLE: fulcrum *Change in direction The closer the fulcrum to the load, the greater the mechanical advantage.

27. 1st lever: Examples • see saw • paint can opener • crow bar • door on hinges See Lab: Exploring Levers

28. 2nd class lever p. 142 The output force does work on the Resistance is AKA the load load What’s in the middle? FLE: load (or resistance) *No change in direction

29. 2nd class lever: Examples • wheelbarrow • nutcracker • garlic press See Lab sheet

30. 3rd class lever p. 142 The input force is AKA as your Resistance is AKA the load effort What’s in the middle? FLE: effort *No change in direction

31. 3rd class lever: Examples • hammer • broom • fishing pole See Lab sheet

32. Wheel and axle p. 144Describe: • Two rounded objects that move together The larger object is the _____________ The smaller object is the ______________ wheel axle The larger the wheel, the longer the distance and the greater the MA.

33. Some wheels are NOT simple machines. They only reduce friction between two surfaces that are rubbing together. Let’s check your worksheet now to see if you understand the difference. Refer to your worksheet on wheels. reduce friction wheel and axle

34. Wheel and axle p. 144 Gears are a special type of wheel and axle. They have teeth that interlock with other gears.

35. Wheel and axle: Examples • faucet • doorknobs • steering wheels • screwdrivers • wrenches • egg beaters

36. pulley p. 143Describe: • a grooved wheel that holds a rope or cable What are pulleys used for? lifting

37. Fixed pulley p. 143 To determine the MA of a pulley, count the support ropes that are pulling UP. See Lab: Exploring Pulleys MA = 1 This pulley only changes The direction of the force.

38. Movable pulley p. 143 Count the support ropes pulling UP to determine the MA. 10 N force MA = 2 This pulley multiplies your force by two. You need half the effort. 20 N block

39. Block and tackle pulley system p. 143 Count the support ropes to determine the MA. 5 N force MA = 4 This pulley multiplies your force by four. You need one-fourth the effort. 20 N block

40. What is the MA of the compound pulley we used in lab? MA = 3 This pulley multiplies your force by three. You need one-third the effort.

41. Pulley: Examples • mini-blinds • hoists in a garage • flag poles • sailing ships

42. A fixed pulley is shown. A fixed pulley can make work easier by • A. Changing the size of the input force needed to lift an object • B. Changing the direction of the force needed to lift an object • C.Changing the size and direction of the force needed to lift • an object • D. Changing the amount of work that must be done

43. A fixed pulley is shown. A fixed pulley can make work easier by • A. Changing the size of the input force needed to lift an object • B. Changing the direction of the force needed to lift an object • You pull down, object goes UP. MA = 1 • C.Changing the size and direction of the force needed to lift • an object • D. Changing the amount of work that must be doneNEVER!

44. This moveable pulley makes work easier by • A Changing the size of the input force needed to lift an object • B Changing the direction of the force needed to lift an object • C Changing the size and direction • of the force needed to lift an object • D Changing the amount of work that • must be done

45. This moveable pulley makes work easier by • A Changing the size of the input force needed to lift an object • You pull UP, the block moves UP. However, there are 2 • ropes pulling UP, so the MA = 2. (change in force) • B Changing the direction of the force needed to lift an object • C Changing the size and direction • of the force needed to lift an object • D Changing the amount of work that • must be done NEVER!!

46. The man in the picture is using a pulley system or a block and tackle. A pulley system can make work easier by • A Changing the size of the input force needed to lift an object • B Changing the direction of the force needed to lift an object • C Changing the size and direction • of the force needed to lift an object • D Changing the amount of work • that must be done

47. The man in the picture is using a pulley system or a block and tackle. A pulley system can make work easier by • A Changing the size of the input force needed to lift an object • B Changing the direction of the force needed to lift an object • C Changing the size and direction • of the force needed to lift an object • Pull down, object UP. • Two support ropes, MA = 2, half the • effort force is needed to lift the block. • D Changing the amount of work • that must be doneNEVER!

48. (Are they really that simple?!) Sure!! Now that you have learned all about them! Study your notes tonight!