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Chapter 6

Chapter 6. Simple Machines. Simple Machines. Wedge Cam Screw Lever Pulley Wheel & Axle Hydraulic press. Black Box Machine. Use input force to do work Ideal Machine – input work equals to output work (no losses) We can change the amount of force needed to do the work. Inclined plane.

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Chapter 6

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  1. Chapter 6 Simple Machines

  2. Simple Machines • Wedge • Cam • Screw • Lever • Pulley • Wheel & Axle • Hydraulic press

  3. Black Box Machine • Use input force to do work • Ideal Machine – input work equals to output work (no losses) • We can change the amount of force needed to do the work

  4. Inclined plane • Pushing a box up inclined plane with incline angle  (no friction) • Lift straight up • Using inclined plane • Hence reduced force needed • But

  5. How to characterize Machine? • Ideal Mechanical Advantage • Geometrical construction • Ratio of output force to input force for ideal machine • Can get IMA of 30-100 or more • Jack & chain hoist

  6. Back to Inclined plane • Pushing a box up inclined plane with incline angle  (no friction) • Lift straight up • Using inclined plane • Hence reduced force needed • But

  7. Actual Mechanical Advantage • Energy losses in machine • Define AMA:

  8. Efficiency of Machine • How “good” is a given machine? • In terms of power

  9. Example—Pulley Systems 20 kg load can be lifted with 65 N force. Pulling rope 150 cm lifts load 30 cm. Find IMA, AMA, Eff?

  10. More simple machines • Wedge • Screw Jack (cam r, pitch p) • Lever (Fulcrum) • Pulley • Hydraulic press

  11. Example If it takes 100 ft-lb of torque to tighten an engine bolt. How long should the wrench be if 60 lb of force is applied?

  12. More on Pulley Systems • IMA of a block and tackle equals to the number of strands supporting the moving block.

  13. Example—Pulley Systems 20 kg load can be lifted with 65 N force. Pulling rope 150 cm lifts load 30 cm. Find IMA, AMA, Eff? How many strand?

  14. Example A pulley can lift 5000 N using 1000 N force. If the IMA is 20, what is the efficiency of the system?

  15. Hydraulic Press • Volume fixed (cross-section area A) • IMA • Almost no losses

  16. Example Compressed air furnishes a force of 60 N to the 0.8 cm^2 area of an oil line that is used to lift a piston in a car lift. What must be the cross sectional area to be able to lift 1100kg vehicle?

  17. Combining machines • Machines in series • Output of 1st is the input of 2nd, etc. • Break 2x2

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