Presentation on theme: "What do simple machines do for us anyway?"— Presentation transcript:
1 What do simple machines do for us anyway? Mechanical AdvantageWhat do simple machines do for us anyway?
2 There are four ways that a machine helps us to do work. Transfers our effort force from one place to another. Ex: seesawMultiply your effort force Ex: crowbarMagnify speed and distance Ex: baseball batChanging the direction of the force. Ex: pulley on the flagpole
3 There are 2 types of mechanical advantage. IMA – Ideal mechanical advantage.This is the number of times a machine is designed to multiply your effort force.It is based on measurements of the machine.Ignores frictionAMA – Actual mechanical advantageThis is the number of times the machine actually multiplies your effort force.AMA = resistance force/effort force.Includes the effects of frictionIMA is always larger than AMA.
4 Mechanical Advantage Definition - a quantity that measures how much a machine multiplies force or distanceTwo typesActual: measures the actual forces action on a machine- AMA = output forceinput forceIdeal: measures the mechanical advantage in the absence of friction- IMA = input distanceoutput distance
5 Mechanical Advantage Problems Q: Alex pulls on the handle of a claw hammer with a force of 15 N. If the hammer has a actual mechanical advantage of 5.2, how much force is exerted on a nail in the claw?A: output force = (5.2)(15N) = 78 NQ: If you exert 100 N on a jack to lift a 10,000 N car, what would be the jack’s actual mechanical advantage (AMA)A: AMA= 10,000 N / 100 N = 100
6 Mechanical Advantage Problems Q: Calculate the ideal mechanical advantage (IMA) of a ramp that is 6.0 m long and 1.5 m high? A: IMA = 6.0m / 1.5m = 4.0 Q: The IMA of a simple machine is 2.5. If the output distance of the machine is 1.0 m, what is the input distance? A: Input distance = (2.5)(1.0m) = 2.5 m
7 Efficiency of Machines Definition- a quantity, usually expressed as a percentage, that measures the ratio of useful work inputFormula- Efficiency = useful work outputwork input- % of work input that becomes work output- due to friction, efficiency of any machine is always less than 100%
8 Efficiency ProblemsQ: Alice and Jim calculate that they must do 1800 J of work to push a piano up a ramp. However, because they must also overcome friction, they must actually do 2400 J of work. What is the efficiency of the ramp? A: 1800 J/ 2400 J x 100 = 75% Q: If the machine has an efficiency of 40%, and you do 1000 J of work on the machine, what will be the work output of the machine? A: Work Output = (Efficiency x work input) / 100% Work Output = (40% x 1000 J) / 100% = 4.0 x 102 J
9 Simple Machines Definition - one of the six basic types of machines 2 types or families1. lever2. inclined planes
10 LeversDefinition- a rigid bar that is free to move around a fixed pointex. screwdriverall levers have a rigid arm that turns around a point called the fulcrumforce is transferred from one part of the arm to anotheroriginal input force can be multiplied or redirected into output forcelevers are divided into 3 classes, based on the locations of the input force, output force, and the fulcrum
11 There are 3 Classes of Levers Depends on the location of 3 items:1. Fulcrum – fixed point on a lever2. Effort Arm – the part of the lever that exerts the effort force.3. Resistance Arm – the part of the lever that exerts the resistance force. EA RA
12 1st Class Lever Changes the direction of the force Multiplies effort forceMagnifies speed and distanceEx: seesaw, crowbar, scissors
13 2nd Class Lever Multiply effort force Mechanical advantage is always greater than 1.Ex: bottle opener, boat oars, wheel barrow
14 3rd Class Lever Magnifies speed and distance Mechanical Advantage always less than 1Ex: baseball bat, golf club, broom, shovel
15 Wheel and Axis Definition - simple machine that consists of two disks or cylinders, each one with a different radiusex. steering wheel, screwdrivermade of a level or a pulley (wheel) connected to a shaft (axle)small input force, multiplied to become a large output force
16 Inclined Planes Definition - slanted surface along which a force moves an object to a different elevationex. knife, ax, zipper, wedge, screwramp redirects the force applied to lift object upwardturns a small input force into a large output force by spreading the work out over a large distance- wedge: functions as two inclined planes back to back, turning a downward force into two forces directed out to the sides-screw: an inclined plane wrapped around a cylinder
17 PulleysDefinition- a simple machine that consists of a rope that fits into a groove in a wheel.- very similar to a leverpoint in the middle of the pulley is like a fulcrumrest of the pulley acts like the rigid arm3 Types of Pulleys- fixed pulleys- moveable pulleys- pulley system
20 1. What is the IMA of this pulley system. 2 1. What is the IMA of this pulley system? Ignoring friction, if you want to lift the resistance 3 meters what will the effort distance be? Ignoring friction how much effort force will be necessary to lift a load of 15 newtons? 4. How much work is done?
21 Compound Machines Definition - a machine that is made of more than one simple machineex. scissors, jacks, bicycle, washing machine, car, clock
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