Mechanical Advantage & Efficiency WORK, WORK, WORK! A “Work” Fundamental: A person CANNOT get out of doing work…one can only sacrifice force for distance or vice versa (Reminder: Work = Force x Distance) Work input = Work output = Kinetic Energy F x D (input) = F x D (output) = ½ mv2 F=5 D=2 F = 10 KE = 10 J D=1 Simple Machines Work can be re-distributed by simple machines, of which there are 6: WHEEL & AXLE Compound Machines Any combination of simple machines is called a compound machine. Example: Can opener – Wedge (teeth) – Wheel & axle (crank) – Lever (handle) How many machines can you count? Mechanical Advantage Calculating the “ease” of a machine is called the Mechanical Advantage (MA). The higher the mechanical advantage number, the less force is needed. – Example: an MA of 2 means that it is 2x easier to do, or ½ the force is needed. IMA Ideal Mechanical Advantage (IMA): The theoretical MA if NO friction was involved. IMA for a pulley is the # IMA for a lever is calculated by… of strings DIRECTLY supporting the object… Effort Distance 2 = Resistance Distance 1 IMA = 2 ED=2 RD=1 AMA Actual Mechanical Advantage (AMA) is the REAL advantage, and is less than IMA because of friction. AMA = Resistance Force (RF) = force by machine Effort Force (EF) force by you AMA is always less than IMA…why? FRICTION is the culprit! Efficiency Efficiency: The percentage of work input that gets directly transferred to work output. (the rest is lost mainly to friction) 100% efficiency only occurs theoretically or “ideally” (hence IMA) Efficiency Calculate efficiency 3 different ways: 1) (Actual) AMA x 100 = _____ % (Ideal) IMA 2) Work (Output) x 100 = ______% Work (Input) 3) Resistance Force x Resistance Distance x 100 = ___% Effort Force x Effort Distance RF x RD EF X ED Assignment 1. RF = 6000 N EF= 4000N MA=________________ 2. RD = 40 m ED= 1200 m MA=________________ 3. Using a lever to move a boulder, Ben applies 256 newtons of force and moves the lever 12.0 meters. The weight of the boulder is 540 newtons. If the boulder is moved 0.20 meters, what is the percent efficiency of the lever? 4. It took 150 N of force for Andy to lift a box weighing 2350 N with a pulley. What is the mechanical advantage of the pulley?_____________ Was this an ideal or actual mechanical advantage? ______________ 5. John wants to lift a box weighing 82 N up on to a shelf that is 1.2 m high . If he does this task in 16 seconds, how much power will be needed?
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