2Review Work = Force * distance measured in Joules [newton meters] this remains true using effort force or resistance forcePower = Work / timemeasured in Joules per secondMechanical Advantage = Force(out) / Force(in)Efficiency = Work(out) / Work(in) * 100
3Machines A Simple Machine accomplishes the work in one motion. A Compound Machine is made up of two or more simple machines. Most machines are compound machines.
4Simple Machines There are six types of simple machines: Lever Wheel-and-AxlePulleyInclined PlaneWedgeScrew
5Helpful NoteALL of the equations for the mechanical advantage of different types of machines will be given to you for the test [which will take place tentatively on Monday, 2/8].Ideal vs. Actual Mechanical EfficiencyIdeal = according to the equationActual = taking into account the efficiencyex: MA = 2 but machine only has a 94% efficiency2 = the ideal MA2* .94 = actual efficiency. MA = 1.88
6Lever Bar Fulcrum A Lever is comprised of: a bar (straight or curved) a fixed point called the fulcrum on which the bar pivotsBarFulcrum
7LeverThe distance from where the effort force is applied to the fulcrum is the Effort Arm of the lever.this is where your effort is doneEffort Arm
8LeverThe distance from the fulcrum to where the resistance force is applied is the Resistance Arm.Resistance Arm
9Lever There are three classes of levers: class is determined by where the location of the effort force, resistance force (load), and the fulcrum
10Lever 1st class lever: see-Saw (Teeter-Totter) prying up a lid by pushing down on a barpairs: scissors, pliers, hedgeclippers
11Lever2nd class lever:doorwheelbarrow armspairs: shears, nutcracker
12Lever 3rd class lever: NOTE: MA = < 1 effort increases to increase distance of loadtweezers!anything you swingbat, sword, stick, golf clubbrooms, rakes, mops
13MALever The MA of a lever is calculated as: MALever = Effort Arm Resistance Arm(again, both in units of length, so there are no MA units)The longer the effort arm, the more the MA [the better it is for you]recall: increase distance, less force
14PracticeWhat is the MA of a lever with an Effort Arm of 6 m and a Resistance Arm of .3 m?Which type of lever does not increase the force output of the machine?If a lever has a MA of 9, and a force of 6 N is applied, how much force will the lever apply?
15Wheel-and-AxleWheel & Axle - a simple machine made of two circles of different diameters that rotate together.The outer circle (wheel) is turned with less force over a larger distance so that the inner circle (axle) turns with more force over a shorter distance.Ex. Steering wheels, door knobs, faucet handles
16MAWheel&Axle MA = radiusWheel radiusAxle Explains how to steer larger vehicles with less force
17PracticeWhat is the MA of a Wheel with a 50 cm radius connected to an Axle with a 2.5 cm radius?
18PulleyPulley - a simple machine comprised of a wheel with a rope or chain running around it.The MA of a pulley system is equal to the number of ropes which support the object, because the weight is distributed.MA = 1no differenceMA = 2no differenceMA = 3no differenceMA = 4no difference
19Pulley There are two types of pulleys Fixed do not move, merely redirect forceMoveableattached to the object being pulled and multiply forcerises and falls with the object
20PulleyBlock and Tackle System - a multiple-pulley system where large amounts of distance are converted into force.composed of a fixed pulley & a moveable pulleyMA = number of supporting ropes
21Practice 2 What is the effort force? [give in pounds of force] 35 lbs What is the MA of this pulley system?2What is the effort force? [give in pounds of force]35 lbs
22Practice 3 What is the effort force? [give in pounds of force] What is the MA of this pulley system?3What is the effort force? [give in pounds of force]23.3 lbs
23PracticeWhat is the Force Output of this pulley system?50 N