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Simple Machines

Simple Machines. Which of these is a machine?. 1. What is a Machine?. Machine- a device that you can use to do work in a way that is easier or more effective. Transfers mechanical energy from one object to another. Examples: Bulldozer Doorknob Hammer Shovel.

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Simple Machines

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  1. Simple Machines

  2. Which of these is a machine?

  3. 1. What is a Machine? • Machine- a devicethat you can use to do work in a way that is easier or more effective. • Transfers mechanical energy from one object to another. • Examples: • Bulldozer • Doorknob • Hammer • Shovel

  4. 2. How do Machines Make Work Easier? • Change the amount of force. • Example: Hammering a nail. • Change the direction of force. • Example: Opening window blinds • Change the distance of force. • Example: Sweeping the floor.

  5. 3. Two Forces Involved When Using a Machine • Input Force(IF)- The force applied to a machine. Also called “Effort Force.” • Output Force (OF)- The force applied by the machine. Also called “Resistance force.”

  6. 4. Input and Output Force a. OF (Output Force) equals the weight of the object moved. b. Example: You push a desk across the floor. • IF= the push you give on the desk • OF= weight of the desk c. Example: You push a wheelbarrow filled with rocks. • IF= the push you give on the wheelbarrow • OF= weight of the rocks

  7. 5. Mechanical Advantage • The number of times a machine multiplies the input force (IF). • Formula: MA = Output force = OF Input force IF

  8. 6. Practice: Mechanical Advantage What is the MA of a crowbar when you apply 200 N of force to raise an object weighing 2,000 N? MA = OF/IF MA = 2,000 N 200 N MA = 10 No Units for M.A.!

  9. What is the MA of a forklift that requires 480 N of input force and gives 6,600 N of output force? Round to nearest whole number MA = OF/IF MA = 6600 N 480 N MA = 14 No Units for M.A.!

  10. Efficiency

  11. A. Factors of Efficiency • Output Work- Work done by a machine. • Input Work- Work done on a machine.

  12. B. Efficiency Definition Efficiency- comparison of output work to input work. Expressed as a percentage (%).

  13. C. Efficiency Equation Efficiency = Output work x 100% Input work E = OW x 100 % IW Units of Measure: Work = Joules (J) Efficiency = percentage (%)

  14. D. Practice Problems: 1. You cut the lawn with a hand mower. You do 250,000 J of work to move the mower. If the work done by the mower in cutting the lawn is 200,000 J, what is the efficiency of the lawn mower? Efficiency = Output work x 100% Input work Efficiency = 200,000 J x 100% 250,000 J Efficiency = 0.8 x 100% Efficiency = 80%

  15. 2. Suppose you left your lawn mower outdoors all winter. It’s now rusty. Of our 250,000 J of work, only 100,000 J go to cutting the lawn by the mower. What is the efficiency of the lawn mower now? Efficiency = Output work x 100% Input work Efficiency = 100,000 J x 100% 250,000 J Efficiency = 0.4 x 100% Efficiency = 40%

  16. E = OW X 100% IW • An old pair of garden shears requires 3,000 J of input work. The gardening shears give 2,200 J of output work. How efficient are the gardening shears? • What force caused the gardening shears to become less efficient? E = 2,200 J X 100% 3,000 J E = 0.73 X 100% E = 73% Friction- rust, parts becoming too tight/loose

  17. E. Machines in Action Efficiency is usually reduced because of friction. List the three types of friction: • Sliding friction • Rolling friction • Fluid friction Friction causes some of the mechanical energy in a machine to be converted to thermal energy. Thermal energy is usually unwanted!

  18. Activity With your Lab Partner With your lab partner, examine the machine at your table. Try to carefully operate it. Observe and describe where friction might occur and list which type of friction is occurring in the space provided below.

  19. F. Why are Machines not 100% Efficient? • Actual mechanical advantage- the mechanical advantage a machine produces in a real situation. Efficiency is usually lost because of friction. • Ideal mechanical advantage- mechanical advantage in the absence of friction.

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