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Simple Machines and Mechanical Advantage Machine– is an instrument that makes work EASIER.
Rube Goldberg Creations Passing man (A) slips on banana peel (B) causing him to fall on rake (C). As handle of rake rises it throws horseshoe (D) onto rope (E) which sags, thereby tilting sprinkling can (F). Water (G) saturates mop (H). Pickle terrier (I) thinks it is raining, gets up to run into house and upsets sign (J) throwing it against non-tipping cigar ash receiver (K) which causes it to swing back and forth and swish the mop against window pane, wiping it clean. If man breaks his neck by fall move away before cop arrives.
Honda Commercial http: //www. boardsmag. com/screeningroom/commercials/581
Simple Machines and Work 2 types of work involved with machines: 1. Work input– the work that goes INTO the machine WORK INPUT = Effort Force X Effort Distance l Effort Force is the force applied TO the machine. (usually what YOU apply to the machine) l Effort Distance is the distance over which you apply force.
Simple Machines and Work 2. Work Output– the work done by the MACHINE WORK OUTPUT = Resistance Force X Resistance Distance l Resistance Force is usually the weight of the object being moved. l Resistance Distance is the distance the object is moved EVEN if there was no machine.
IMPORTANT! Machines DO NOT INCREASE the work put into them, they just make work easier. l Allows you to use less force!!!
Mechanical Advantage: how many times the machine multiplies your effort force. l how much the machine REDUCES how much effort force you have to apply. l What you lose in EFFORT FORCE, you gain in EFFORT DISTANCE.
Mechanical Advantage Example: If you are using a machine that has a mechanical advantage of 2. 5, you will have increased your EFFORT DISTANCE by 2. 5 times. l This allows you to REDUCE the EFFORT FORCE needed by 2. 5 times.
Mechanical Advantage Ideal Mechanical Advantage (IMA)= l Assumes that there is NO FRICTION involved. IMA = Effort Distance/ Resistance Distance or Resistance Force/ Effort Force Ed / R d or R f / Ef
6 Types of Simple Machines 1. 2. 3. 4. 5. 6. Inclined Plane Wedge Screw Lever Wheel and Axle Pulley All are forms of inclined planes
Inclined Plane l A flat slanted surface Ef Rf Ed The weight of the box is the Rf Rd
Inclined Plane IMA = Ed / Rd Rf IMA or Ef IMA = Rf / Ef 3 m ete 1. 5 meter rs Ed 3 m / 1. 5 m = 2 250/ ? ? ? = Box weighs 250 N Rd
Inclined Plane and Work = Force X Distance • Use either: Resistance Force and Resistance Distance OR Effort Force and Effort Distance 3 m ete 1. 5 meter Work = Rf x Rd rs Box weighs 250 N X 1. 5 m = 375 Joules
Wedge l A moving inclined plane The longer and thinner the Wedge (inclined plane), the higher The IMA. (the better the machine)
IMA of a Wedge A wedge is 2 inclined Planes together. 6 cm 10/6 = 1. 67 IMA is 3. 34 m 10 c 10/6 = 1. 67 _______ 3. 34 10 cm Ed/ Rd 6 cm Calculate the IMA of each Inclined plane and add together.
Screw l An inclined plane wrapped around a central bar to form a spiral
IMA of a Screw Higher IMA, MORE THREADS Lower IMA, less threads With more threads, turn the screw for a LONGER DISTANCE so can use LESS FORCE.
Lever l l Rigid bar that is free to pivot about a fixed point. Fulcrum: the fixed point on a lever.
Classes of Levers force Rf ____ Rf F 2 Class R 3 rd Class E 1 st Class _______ nd force Rf force Effort DISTANCE = Effort ARM • from the fulcrum to the point of Effort force. Resistance DISTANCE = Resistance ARM • From the FULCRUM to the point of Resistance force
1 st Class Lever Ef Ef Rf Rf Changes direction of the force
2 nd Class Lever Rf Ef
3 rd Class Lever Does not multiply your effort force, It just makes it a little easier (or increases speed)
Levers and IMA What is the IMA of the following lever? . 25 m What kind of lever is it? Ef 2 m N 00 3
Levers and IMA What is the IMA of the hockey stick? Ef = 60 N. 5 m 2. 5 m What type of lever is the hockey stick? Rf
Wheel and Axle • Made up of 2 circular objects of different sizes Wheel– the large circle • Effort distance Axle– the smaller circle. • Resistance Distance
Wheel and Axle
Wheel and Axle and IMA 24 cm 6 c m What is the IMA? Ed/Rd
Pulley l A rope, belt or chain wrapped around a grooved wheel.
Type of Pulleys Fixed Pulley: pulley attached to a structure. l Changes the direction of the Effort Force l DOES NOT multiply your effort force üCalculate IMA by counting the number of SUPPORTING ropes. IMA = 1
Types of Pulleys Movable Pulley: attach pulley to a moving object • Multiplies force, but does not change direction IMA = 2
Compound Pulleys l Combination fixed and movable pulleys IMA =
Examples of Pulleys
Block and Tackle System
I guess that’s It! Whew! l Any Questions?