2. What is Work?  Work: A force must be exerted on an object and the object must move in the direction of the force  No movement means no work  Movement in a direction not of the force means no work

3. How do you calculate work?  Work = Force x Distance  Joule: SI unit for work

4. What is power?  Power: rate at which work is done  Power = Work/time  Watt: SI unit for power

5. Section 2: What is a Machine?  Example: Use a machine to change a flat tire  Machines: make work easier  Machine: device that helps make work easier by changing the size or direction of a force  Not all machines are complicated  Examples: tire iron, jack, scissors

6. Work in, Work out  Two kinds of work are always involved when machines are used  1. work done on the machine  2. work done by the machine on another object  Work—force applied through a distance  Work input—work you do on the machine  Work output—work done by a machine

7. How machines Help  Machines do not increase the amount of work done  Work output can never be greater than work input

8. Machines Do Not Save Work  Machines make work easier because they change size or direction of input forces

9. The Force-Distance Trade-off  When machines change size of force the distance must also change  When one (distance or force) increases the other must decrease

10. Mechanical Advantage  Some machines make work easier than others  Mechanical advantage—how many times the machine multiplies the force  MA = output force/input force  Ex. 500 N/50N = 10  Output of 10 means that the output force is ten times bigger than the input force

11. Mechanical Advantage  The larger the Mechanical Advantage, the easier a machine makes your work  MA increases the distance the output force moves the object

12. Mechanical Efficiency  Work output can never be greater than work input  Work output always less than work input  More efficient machines have to do less work to overcome friction  ME = work output/work input X 100  ME is expressed as a percentage  Ideal machine—machine that is 100 % efficient (does not exist)

13. Section 3: Types of Machines  Six simple machines: lever, inclined plane, wedge, screw, wheel and axle, pulley  Simple machines combine to form compound machines

14. Levers  Simple machines that consist of a bar that pivots at a fixed point (fulcrum)  3 Classes of Levers based on the location of the fulcrum, load, and input force

15. First Class Lever  Fulcrum is in-between the input force and the load  Change direction of the input force  Can increase force or distance  Example: hammer pulling a nail, seesaw, rowing Fulcrum Load Input

16. Second Class Lever  Load is in-between fulcrum and input force  Does not change direction of the input force  Example: bottle opener, wheel barrow Fulcrum Load Input

17. Third Class Lever  Input force is in-between fulcrum and the load  Does not change direction of the input force  Does not increase input force  Example: hammer pounding a nail Fulcrum LoadInput

18. Inclined Planes  Inclined Plane: simple machine that is a straight slanted surface  Example: ramp  Makes work easier by reducing input force and increasing distance  Mechanical Advantage: the longer the inclined plane compared to its height the greater the advantage  MA= Length of inclined plane/height of inclined plane

20. Wedges  Wedge: double inclined plane that moves  Ex. Knives, doorstop, plows, axe heads, chisels  Mechanical Advantage: the longer and thinner the wedge, the greater the mechanical advantage  MA = length of wedge/greatest thickness of wedge

21. Screws  Screw: inclined plane wrapped around a spiral  Ex. Bolt, drywall screw, jar lid  Mechanical Advantage: imagine unwinding a screw to form an inclined plane  The longer the spiral of a screw, the closer together the threads, the greater the mechanical advantage

22. Wheel and Axle  Wheel and axle: consists of two circular objects of different sizes  Examples: handle of fishing reel, knob, doorknob, wrenches, ferris wheels, screwdrivers  MA = radius of the wheel/radius of the axle

23. Pulley  Pulley: simple machine that consist of a grooved wheel that holds a rope or cable  Load attaches to one end of rope and input force exerted on the opposite end  Types: fixed, movable, block and tackle (combines fixed and moveable pulleys)

24. Fixed Pulley  Pulley attached to something that does not move  Only change the direction of the force  Do not increase force  Input force and output force are the same  MA of (1)  Ex. Elevator

25. Moveable Pulley  Pulley attached to something that moves  Does not change the direction of the force  Increases the force  Must exert input force greater distance that load is moved because both sides of rope must move to lift load  MA: Equal to the # of rope segments that support a load

26. Block and Tackle  Fixed pulley and movable pulley used together  MA can be large if several pulleys used  Block and Tackle multiplies your input force but the distance must increase  Ex. Input force multiplied 4 times, must pull rope 4m to lift load 1m

27. Compound Machine  Compound Machines: made up of two or more simple machines  Ex. Block and tackle pulley, can opener, scissors, zipper  Mechanical Efficiency: The more moveable parts the lower the mechanical efficiency; Reduction of friction can increase efficiency