Work & Simple Machines

1. Work & Simple Machines

2. Define / Describe WORK • Work is done when a force causes an object to move in the direction that the force is applied. • The formula for work is: W = F X D • If there is no movement, there is no work

3. Two things must happen for work to be done. What are they? • A force must applied to an object • The object must move in the same direction as the force.

4. What is purpose of a machine? To make work easier.

5. How do machines make work easier? Remember that Work = Force X Distance) ***Increasing the distance(D) allows us to decrease the force accomplished with the same amount of work(W).*** They can also change the direction

6. What is mechanical advantage? The number of times a machine multiplies the effort or input force.

7. What are the 6 types of simple machines? • There are three simple machines: • The lever, the pulley, and the inclined plane The wheel and axle, the wedge, and the screw are modifications of these simple machines.

8. What is a compound (or complex) machine? A machine made up of two or more simple machines.

9. Types of Simple Machines

10. The Lever

11. The Levera rigid bar that is free to turn about a fixed point called the fulcrum Every Lever has three (3) parts: 1.  Resistance Force, Input Force or Load, What you are trying to move or lift. 2.  Effort Force or Output Force - The work done on the Lever. 3.  Fulcrum – A fixed pivot point.

12. The Lever

13. 1st Class Lever

14. 1st Class Lever • The Fulcrum (fixed pivot point) is located between the Effort (Input) and the Resistance (Output) Forces.  • The effort and the resistance move in opposite directions.  • The effort force pushes down in order to lift the resistance or load.

15. 1st Class Lever • When the fulcrum is closer to the effort than to the load: • there is a loss in force • There is a gain in speed and distance.

16. 1st Class Lever • When the fulcrum is closer to the load than to the effort: • there is a loss in speed and distance • There is a gain in force.

17. 1st Class Lever • When the fulcrum is midway between the effort and the load: • there is no change in force, speed or distance

18. 1st Class Lever • Examples: • Seesaw • Crowbar • Scissors

19. 2nd Class Levers

20. 2nd Class Lever • The load is between the effort and the fulcrum. • The fulcrum is at one end of the lever. • The fulcrum is usually closer to the load. • Produce a gain in force.

21. 2nd Class Levers • Examples: • Wheelbarrow • Bottle opener • Nutcrackers

22. 3rd Class Levers

23. 3rd Class Levers • The effort is between the load and the fulcrum. • There is usually a loss in force, but a gain in speed and distance.

24. 3rd Class Levers • Examples: • Broom • Shovel • Fishing rod

25. The Pulley

26. The Pulley • A pulley changes the direction of the force: • Instead of lifting up, you can pull down using your body weigh against the load (what is being lifted) • A pulley gains nothing in force, distance or speed

27. The Pulleya wheel that turns around an axle • A pulley is a grooved wheel that turns around an axle (fulcrum), and a rope or a chain is used in the grove to lift heavy objects. • A pulley may be fixed, moveable, or used in combination.

28. The Fixed Pulley • Is attached to something that doesn't move such as the ceiling or wall) • It acts as a first class lever with the fulcrum located at the axis • Instead of a bar the pulley uses a rope or chain.

29. The Pulley • A moveable pulley acts as second class lever • the load is between the fulcrum and the effort

30. The Pulley • A compound pulley is a system of movable pulleys. • Mechanical advantage can be increased by using more than one pulley.

31. The Inclined Plane

32. The Inclined Planea sloping surface that does not move • An inclined plane provides for NOT Less work but less effort.  • The trade off is greater distance to travel.

33. The Inclined Plane • Used to reduce the force needed to overcome the force of gravity when lifting or lowering a heavy object.

34. The Inclined Plane

35. The Screw

36. The Screwan inclined plane wrapped around a central cylinder • A Screw has two (2) parts: • The Body – Cylinder Post • The Thread – Inclined Plane wrapped around the cylinder.

37. The Screw • Functions of the screw • To fasten things – the standard screw or nuts & bolts. • Drill bits are screws used to make holes. • A jackscrew is used to lift heavy objects; car jack.

38. The Screw • When you turn a screw: • The input force is changed by the threads into an output force. • The output force pulls the screw into the materials. • Friction between the threads & the material holds the screw in place.

39. The Wedge

40. The Wedgean inclined plane that tapers to a sharp edge • The wedge used to increase force.  • The material remains in place while he wedge moves through it. • A wedge changes the direction of the input force.

41. The Wedge • Wedges can be forced between two things to hold them tightly together, like nails or a doorstop. • Wedges can be used to split, cut or fasten.

42. The Wheel & Axle

43. The Wheel & Axlea wheel connected to a rigid pole • The Wheel & axle is a modified lever: • The center of the axle acts as a fulcrum – making the wheel a lever that rotates around in a circle.

44. Go to this link for more information about machines. Remember to hit the “back” button on your browser to return to this slide show. http://www.usoe.k12.ut.us/curr/science/sciber00/8th/machines/sciber/intro.htm

45. DE Streaming • Warm Up/ Review: Quick video of the simple machines Work, energy, and simple machines