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Aim: What is work?

Date: 11/1/2007. Aim: What is work?. Homework: ABS & OWE Homework & Quizzes due tomorrow. What is work?. Scientists definition: work is only done on an object when a force is applied to that object & the object moves over a distance. What is a force?.

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Aim: What is work?

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  1. Date: 11/1/2007 Aim: What is work? Homework: ABS & OWE Homework & Quizzes due tomorrow.

  2. What is work? Scientists definition: work is only done on an object when a force is applied to that object & the object moves over a distance What is a force?

  3. The Greek god Atlas is carrying the world on his shoulders. Is he doing work?

  4. How is work measured? Work = Force X Distance W F D What is the standard unit for work & energy? W = F x D Joules = Newton-meter

  5. 1) John uses a force of 20 newtons to push a box across the floor a distance of 3 meters. How much work did John do while pushing the box? W = F x D W = (20 N) x (3 m) W = 60 N-m or 60 Joules

  6. 2) Tara does 0.1 Joules of work by prying the lid off a can. The lid moves a distance of 0.01 meters. How much force did Tara use to open the can? Force = work/distance F = 0.1 J 0.01 m F = 10 N

  7. Date: 11/7/2006 Tuesday Aim: 1. What are 6 simple machines? 2. What is a complex machine? Do Now: 1. What is a machine? 2. Who is the strongest person in the class? (paint can demo) Homework: Complete Handout on Levers & Handout (Work & Power): Write Formulas, Plug in #s, Calculate & give units for #1-5

  8. What is a simple machine? A device (tool) used to make work easier What are various types of simple machines? 1. Lever: a stiff bar (that pivots on a fixed point called a fulcrum) which lifts or moves loads. 

  9. 1 2 3 E R F (What is in the Middle)

  10. 2. Wedge: an object with at least one slanting side ending in a sharp edge, which cuts material apart. (Moving Inclined Plane)

  11. 3. Pulley: • a belt, rope, or chain wrapped around a grooved wheel • Fixed Pulley: • changes the direction of the effort force • Movable Pulley: • Multiplies the effort force

  12. 4. Inclined Plane: slanting surface connecting a lower level to a higher level

  13. 5. Wheel & Axle: • A lever that rotates in a circle around a rigid pole or, • A wheel with a rod, called an axle, through its center lifts or moves loads.

  14. 6. Screw: an inclined plane wrapped around a central cylinder

  15. Compound Machine: 2 or more simple machines working together

  16. Date: 11/5/2007 Wednesday Aim: How is work input & work output calculated? Do Now: Handout – Identifying Simple Machines Homework: Read pgs 160-165 & Answer Self-Check Ques. (1-3) on pg 165

  17. What are the forces involved in using a machine to do work? Effort Force (FE): the force that you put into using the machine 2. Resistance Force (FR): the force that the machine exerts on the object

  18. What are the distances involved in using a machine to do work? Effort Distance (DE): the distance that you move the machine 2. Resistance Distance (DR): the distance that the machine moves

  19. What is work input & how is it calculated? the work that you do in using the machine work input = effort force X effort distance Or Winput = FE X DE

  20. What is work output & how is it calculated? the work that the machine does on the object work output = resitance force X resistance distance Or Woutput = FR X DR

  21. What is the force that opposes Kevin? 250 N 25 M 1000 N 5 M

  22. Why is work input greater than work output? WI = (250 N)(25m) = 6250 J = FE X DE WO = (1000 N)(5m) = 5000 J = FR X DR

  23. Date: 11/6/2007 Tuesday Aim: What is the difference between mechanical advantage & the efficiency of using a machine? Do Now: What is the difference between work input & work output? Homework: Read pages 166 – 174 & Answer Ques. (1-12) on pg 180 (write complete sentences!!!)

  24. What is mechanical advantage? The benefit of using a machine or, The number of times a machine multiplies the effort force

  25. A.M.A. is a comparison of both Forces: A.M.A. = FR/ FE It calculates the actual benefit of using a machine because in reality we have to take the Force of Friction into consideration. What is the mathematical formula for Actual Mechanical Advantage?

  26. I.M.A. is a comparison of both Distances: I.M.A. = DE/ DR Ideal means perfect A perfect machine would not have friction (There is no such thing as a perfect machine!!!) What is the mathematical formula for Ideal Mechanical Advantage?

  27. 1) Suppose you are unable to open a crate with your bare hands. To help you use a crowbar. You have to push the crowbar handle down 20 cm to move the crate lid up 4 cm. What is the ideal mechanical advantage of the crowbar? I.M.A. = DE/ DR I.M.A. = 20 cm / 4 cm I.M.A. = 5

  28. 2) You move a rock by placing a long pole underneath it. You apply a force of 10 Newtons & in turn, the pole exerts a force of 125 Newtons on the rock. What is the Actual Mechanical Advantage of the pole? A.M.A. = FR/ FE A.M.A. = 125 N / 10 N A.M.A. = 12.5

  29. What is efficiency? Comparison of Work Input to Work Output Work Input is always greater than Work Output (friction must be overcome) Most efficient machine has the least amount of friction

  30. What is the mathematical formula for efficiency? Work Output Work Input X 100

  31. What is the efficiency of a bicycle if you do 6 Joules of work in riding it and the bicycle does 5 Joules of work? Efficiency = Work Output Work Input 5 Joules 6 Joules X 100 X 100 = Efficiency = 83.3%

  32. 250 N 25 M 1000 N 5 M =4 = FR/ FE = 1000/250

  33. = 5 = DE/ DR = 25/5 WI = (250 N)(25m) = 6250 J = FE X DE WO = (1000 N)(5m) = 5000 J = FR X DR 5000 6250 Work Output Work Input X 100 = 80% X 100

  34. Date: 11/7/2007 Wednesday Aim: 1. What is the relationship between friction & efficiency? 2. Lab – Its All Uphill Do Now: 1. Take out homework. 2. What is friction? 3. Is there any machine that doesn’t have friction? Homework: Handouts Study for next Wednesday’s Quiz & Thursday’s Exam on Work & Simple Machines

  35. What is a perfect machine? A machine that has no friction & is therefore: 100% Efficient Work Output = Work Input

  36. What does the Law of Machines State? No Machine is 100% Efficient

  37. How can you reduce friction between parts of a machine? Use lubricants such as oil, grease, wax Put wheels on certain parts Use ball bearings

  38. Date: 11/30/2007 Aim: Lab – How can a weak person lift a very heavy object with one hand? Do Now: Who are the smallest & largest people in the class? Homework: Study for tomorrow’s Quiz & Wednesday’s Exam on Work & Simple Machines

  39. Why is work input equal to work output? 5 m 2 N 1 m 10 N WI = (2 N)(5m) = 10 J = FE X DE = FR X DR WO = (10 N)(1m) = 10 J

  40. Is this a perfect machine? Why or Why not? 5 m 2 N 1 m 10 N = FR/ FE = 10/2 = 5 = 5/1 = DE/ DR = 5 WI = (2 N)(5m) = 10 J = FE X DE Work Output Work Input = 10 J 10 J = FR X DR X 100 WO = (10 N)(1m) = 10 J = 100% X 100

  41. 1 2 3 E R F (What is in the Middle)

  42. Identify the Effort Force, Fulcrum, Resistant Force & Class Lever

  43. Date: 11/14/2007 Wednesday Aim: 1. Take & go over quiz. 2. Review: What do you know about Work & Simple Machines? Do Now: Prepare for Quiz Homework: Study for tomorrow’s Exam on Work & Simple Machines ***Make sure to Bring a Pencil & Calculator

  44. Which one is a fixed pulley/movable pulley? IMA = 1 IMA = 2

  45. 25 m 10m 5m 5m I.M.A. = 2 I.M.A. = 5 As the slant decreases, the mechanical advantage increases.

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