3. In science, the word work has a different meaning than you may be familiar with. The scientific definition of work is: using a force to move an object a distance (when both the force and the motion of the object are in the same direction.)

4. According to the scientific definition, what is work and what is not? a teacher lecturing to his/her class a mouse pushing a piece of cheese with its nose across the floor

6. Work = Force x Distance The unit of force is Newtons The unit of distance is meters The unit of work is Newton-meters One Newton-meter is equal to one Joule So, the unit of work is a Joule

7. Work = Force x Distance Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done?

8. Work = Force x Distance Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done? Work = F X D = 20N*10m 200Nm=200 joules

9. Before engines and motors were invented, people had to do things like lifting or pushing heavy loads by hand. Using an animal could help, but what they really needed were some clever ways to either make work easier or faster.

10. Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces.

11. The six simple machines are: Lever Wheel and Axle Pulley Inclined Plane Wedge Screw

12. A machine is a device that helps make work easier by accomplishing one or more of the following functions: Increasing the magnitude of a force Increasing the distance of a force Increasing the speed of a force Changing the direction of a force Transferring a force from one place to another

13. Input force (the force you apply) Output force (force which the machine applies to the task). When a machine takes a small input force and increases the magnitude of the output force, a Mechanical Advantage has been produced.

14. Friction is ignored when calculating IMA. IMA > 1 means it increases force Each machine calculates IMA differently As we cover each machine, put the IMA formula on the grid sheet for that machine

15. AMA is the ratio of output force/input force (R/E). If an input force of 20 newtons and the output force of 100 newtons, the machine has an Actual Mechanical Advantage (AMA) of 5. AMA = R / E Formula is the SAME for all machines Friction decreases the AMA.

16. No machine can increase both the magnitude and the distance of a force at the same time.

17.  A lever is a rigid bar that rotates around a fixed point called the Fulcrum.  Effort Force supplied by you  Resistance Force: force supplied by the machine to move something  There are 3 Classes of levers

18. The class of a lever is determined by the location of the effort, resistance and fulcrum.

19. Note the location of the F, E and R for each type of lever For all levers the following formulas are correct IMA = L E /L R = divide the length of the Effort arm by the length of the Resistance arm (both measured from force to the fulcrum) AMA = Resistance / Effort.

20. The fulcrum is located at some point between the effort and resistance forces. Common examples of first-class levers include see-saw, crowbar, scissors, pliers, tin snips A first-class lever ALWAYS changes the direction of force.

22. the Resistance is located between the fulcrum and the Effort. Common examples of second-class levers include nut crackers, wheel barrows and bottle openers. Advantage: Always increases the force Never changes the direction of force.

25. Effort is applied between the Fulcrum and the Resistance. Examples of third-class lever: tweezers, a rake and your arm Never changes the direction of the force Always produces a gain in speed and distance Always DECREASES the force

26. The wheel and axle is a large wheel rigidly secured to a smaller wheel or shaft, called an axle. When the wheel or axle is turned, the other part also turns. One full revolution of either part causes one full revolution of the other.

27.  IMA =  Radius(wheel) _____________ Radius(axle)  AMA = R/E

28. Can change the direction of a force or Can gain a Mechanical Advantage depending on how the pulley(s) is(are) arranged.

29. Fixed pulley :if it does not rise or fall with the load being moved. A fixed pulley changes the direction of a force; however, it does not increase the force.

30. A Moveable pulley rises and falls with the load that is being moved. A single moveable pulley creates an IMA of 2. It does not change the direction of a force. The IMA of a moveable pulley is equal to the number of ropes that support the moveable pulley. Pulling down strand does not count.

31. Composed of at least 1 fixed and 1 moveable pulley linked IMA = # of supporting strands. PULLING DOWN DOES NOT COUNT AS A SUPPORTING STRAND.

32. An inclined plane is an even sloping surface. A Ramp. The inclined plane makes it easier to move a weight from a lower to higher elevation. IMA = Run/Rise IMA = Effort Distance/ Resistance Distance

33. The IMA of an inclined plane is equal to the length of the slope divided by the height of the inclined plane. IMA(Slope) = run/rise Mechanical Advantage, is derived by increasing the effort distance through which the force must move.

35. The screw is also a modified version of the inclined plane. While this may be somewhat difficult to visualize, it may help to think of the threads of the screw as a type of circular ramp (or inclined plane).

37. INPUT WORK = Effort X Distance the Effort moved IW = E x D E D E is not the same as L E. L E is measured from fulcrum to the E. D E is measured along the direction of movement. OUTPUT WORK = Resistance X Distance the Resistance moved OW = R x D R D R is not the same as L R. L R is measured from fulcrum to the R. D R is measured along the direction of movement.

38. Some output force is always lost due to friction. Efficiency=(Output Work/Input Work)*100 Formula for Efficiency is the same for ALL machines No machine has 100% efficiency due to friction.

40. MachineInput Work(IW) Output Work(OW) IMA AMA R/E Efficiency Output work Input work X 100 Theoretical Effort (TE) R/IMA Lever E x D E D E = Distance the Effort moved R x D R D R = Distance that the Resistance moved L E /L R L E = Length of the effort arm L R = Length of the resistance arm R/E Output work Input work X 100 R/IMA PulleyE x D E R x D R # supporting strands R/E Output work Input work X 100 R/IMA Wheel & AxelE x D E R x D R Radius (wheel) -------------------- Radius (axel) R/E Output work Input work X 100 R/IMA Inclined PlaneE x RunR x RiseRun/RiseR/E Output work Input work X 100 R/IMA WedgeE x Run(length)R x Rise(width) Run/Rise or Length/Width R/E Output work Input work X 100 R/IMA ScrewE x D E R x D R # threads -------------------- 2.5xLength(cm) R/EOutput work Input work X 100 R/IMA Calculations related to Simple Machines KEY

41. 1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building being constructed, or a project supervisor observing and recording the progress of the workers from an observation booth. 2. How much work is done in pushing an object 7.0 m across a floor with a force of 50 N and then pushing it back to its original position? 3. Using a single fixed pulley, how heavy a load could you lift?

42. 4. Give an example of a machine in which friction is both an advantage and a disadvantage. 5. Why is it not possible to have a machine with 100% efficiency? 6. What is effort force? What is work input? Explain the relationship between effort force, effort distance, and work input.

43. 1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building being constructed, or a project supervisor observing and recording the progress of the workers from an observation booth. Work is defined as a force applied to an object, moving that object a distance in the direction of the applied force. The bricklayer is doing more work. 2. How much work is done in pushing an object 7.0 m across a floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is done in 20 sec? Work = 7 m X 50 N X 2 = 700 N-m or J 3. Using a single fixed pulley, how heavy a load could you lift? Since a fixed pulley has a mechanical advantage of one, it will only change the direction of the force applied to it. You would be able to lift a load equal to your own weight, minus the negative effects of friction.

44. 4. Give an example of a machine in which friction is both an advantage and a disadvantage. One answer might be the use of a car jack. Advantage of friction: It allows a car to be raised to a desired height without slipping. Disadvantage of friction: It reduces efficiency. 5. Why is it not possible to have a machine with 100% efficiency? Friction lowers the efficiency of a machine. Work output is always less than work input, so an actual machine cannot be 100% efficient. 6. What is effort force? What is input work? Explain the relationship between effort force, effort distance, and input work. The effort force (E) is the force applied to a machine. Input work (IW) is the work done on a machine. The input work (IW) of a machine is equal to the effort force (E) times the distance (D E ) over which the effort force is exerted.