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."— Presentation transcript:
1 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 numberMA = OF/IFMA = 6600 N480 NMA = 14No Units for M.A.!
3 A. Factors of Efficiency Output Work- Work done by a machine.Input Work- Work done on a machine.
4 B. Efficiency Definition Efficiency- comparison of output work to input work. Expressed as a percentage (%).
5 C. Efficiency Equation Efficiency = Output work x 100% Input work E = OW x 100 %IWUnits of Measure:Work = Joules (J)Efficiency = percentage (%)
6 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 workEfficiency = 200,000 J x 100%250,000 JEfficiency = 0.8 x 100%Efficiency = 80%
7 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 workEfficiency = 100,000 J x 100%250,000 JEfficiency = 0.4 x 100%Efficiency = 40%
9 gardening shears to become less efficient? 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 thegardening shears to becomeless efficient?E = OW X 100%IWE = 2,200 J X 100%3,000 JE = X 100%E = 73%Friction- rust, parts becoming too tight/loose
10 E. Machines in ActionEfficiency is usually reduced because of friction. List the three types of friction:Sliding frictionRolling frictionFluid frictionFriction causes some of the mechanical energy in a machine to be converted to thermal energy. Thermal energy is usually unwanted!
11 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.
12 Tool NameType of FrictionLocation of FrictionScissorsSlidingRollingWhen blades close and openOn the pin that holds blades togetherStaplerWhen top and bottom pieces closeOn the hinge between top and bottomHole PuncherWhen handle pushed on bottom pieceWhen hinges/pins move handleRatchetWhen metal parts grind past each otherWhen socket (bottom) rotatesPliersWhen metal parts grind or touchOn the pin that holds handles togetherCan OpenerWhen metal cogs turn on each otherOn the pin that hold the handles together
13 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.