Presentation on theme: "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."— Presentation transcript:
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.!
A. Factors of Efficiency Output Work- Work done by a machine. Input Work- Work done on a machine.
B. Efficiency Definition Efficiency- comparison of output work to input work. Expressed as a percentage (%).
C. Efficiency Equation Efficiency = Output work x 100% Input work E = OW x 100 % IW Units of Measure: Work = Joules (J) Efficiency = percentage (%)
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%
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%
1.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? 2.What force caused the gardening shears to become less efficient? Friction- rust, parts becoming too tight/loose E = OW X 100% IW E = 2,200 J X 100% 3,000 J E = 0.73 X 100% E = 73%
E. Machines in Action Efficiency is usually reduced because of friction. List the three types of friction: 1.Sliding friction 2.Rolling friction 3.Fluid friction Friction causes some of the mechanical energy in a machine to be converted to thermal energy. Thermal energy is usually unwanted!
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.
Tool NameType of Friction Location of Friction ScissorsSliding Rolling When blades close and open On the pin that holds blades together StaplerSliding Rolling When top and bottom pieces close On the hinge between top and bottom Hole PuncherSliding Rolling When handle pushed on bottom piece When hinges/pins move handle RatchetSliding Rolling When metal parts grind past each other When socket (bottom) rotates PliersSliding Rolling When metal parts grind or touch On the pin that holds handles together Can OpenerSliding Rolling When metal cogs turn on each other On the pin that hold the handles together
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.