Rube Goldberg ProjectRube Goldberg Project Homework Project – you have to build it at Homework Project – you have to build it at

home.home. Perform a task that is very simple in multiple Perform a task that is very simple in multiple

steps using simple machines.steps using simple machines. 5 steps per person on the team5 steps per person on the team

Contraption must work from beginning to end Contraption must work from beginning to end without intervention, once started.without intervention, once started.

Each step must be labeled Each step must be labeled Each step must include a simple machineEach step must include a simple machine Each step must have mechanical advantage calculated Each step must have mechanical advantage calculated

and labeledand labeled Each step must have work calculated and labeled.Each step must have work calculated and labeled.

Bonus Question: What is the efficiency of your Bonus Question: What is the efficiency of your machine (beginning to end)machine (beginning to end)

Due Monday: 2/23Due Monday: 2/23

Work, Power, MachinesWork, Power, Machines

Chapter 9.1 & 9.2Chapter 9.1 & 9.2

What is Work?What is Work? If I push on a lab table really hard for 20 If I push on a lab table really hard for 20

minutes, is that work?minutes, is that work? NoNo

If I push on the wheeled cabinet lightly If I push on the wheeled cabinet lightly and it moves a little, is that work?and it moves a little, is that work? YesYes

If I write on the white-board, is that If I write on the white-board, is that work?work? YesYes

If I sit in my chair and do nothing, is that If I sit in my chair and do nothing, is that work?work? NoNo

What is Work?What is Work? If I think really hard for 30 minutes, is If I think really hard for 30 minutes, is

that work?that work? NoNo

If I watch the TV for 2 hours, is that If I watch the TV for 2 hours, is that work?work? NoNo

If I play Xbox for 10 minutes, am I doing If I play Xbox for 10 minutes, am I doing work?work? YesYes

What is the common denominator What is the common denominator between work and no work?between work and no work?

What is Work?What is Work? Work = Force x DistanceWork = Force x Distance

No force, no workNo force, no work No movement, no workNo movement, no work

Work is measured in Work is measured in joulesjoules One joule is 1 Newton (force) x 1 meter One joule is 1 Newton (force) x 1 meter

(distance)(distance) 1 N*m = 1J = 1 kg*m1 N*m = 1J = 1 kg*m22/s/s22

1 N is 1 kg*m/s1 N is 1 kg*m/s22

What is Power?What is Power? Which has more power? A semi truck Which has more power? A semi truck

or a fast sports car?or a fast sports car? It dependsIt depends

Which requires more power. Which requires more power. Accelerating from 0 to 60 in 10 seconds Accelerating from 0 to 60 in 10 seconds or 6 seconds?or 6 seconds? 6 seconds6 seconds

Why?Why?

What is Power?What is Power? Power = Work/timePower = Work/time

No work, no powerNo work, no power More time = less powerMore time = less power Less time = more powerLess time = more power More power means doing the same work, More power means doing the same work,

fasterfaster Power is measured in WattsPower is measured in Watts

A Watt is 1 joule in 1 secondA Watt is 1 joule in 1 second

Machines & Mechanical AdvantageMachines & Mechanical Advantage Which is easier:Which is easier:

Lifting a car by your self to change a tireLifting a car by your self to change a tire Using a car jack to lift the carUsing a car jack to lift the car

Obviously, using the car jackObviously, using the car jack Why?Why? Because machines make it easier for us to Because machines make it easier for us to

do work!do work!

Machines and Mechanical AdvantageMachines and Mechanical Advantage Machines don’t change the amount of workMachines don’t change the amount of work

They might change the forceThey might change the force They might change the distanceThey might change the distance They might change the direction of the forceThey might change the direction of the force Usually, they change the amount of force by Usually, they change the amount of force by

changing the distancechanging the distance W = force x distanceW = force x distance

Change one up, the other goes downChange one up, the other goes down

Machines and Mechanical AdvantageMachines and Mechanical Advantage

Both a car jack and a ramp reduce the Both a car jack and a ramp reduce the amount of force required, by increasing amount of force required, by increasing the distance.the distance.

Mechanical advantage tell us how Mechanical advantage tell us how much the input force or distance is much the input force or distance is multiplied by the machine.multiplied by the machine.

Machines and Mechanical AdvantageMachines and Mechanical Advantage

For any machine:For any machine: Input work = output workInput work = output work Forces may be differentForces may be different Distances may be differentDistances may be different Work remains constantWork remains constant

Simple MachinesSimple Machines

Common Work AssistantsCommon Work Assistants

Six Simple MachinesSix Simple Machines Inclined PlaneInclined Plane WedgeWedge ScrewScrew LeverLever Wheel and AxleWheel and Axle PulleyPulley

Inclined PlaneInclined Plane Inclined Plane: A Flat, Slanted SurfaceInclined Plane: A Flat, Slanted Surface Purpose: Exert smaller force over Purpose: Exert smaller force over

larger distancelarger distance Ideal Mechanical Advantage:Ideal Mechanical Advantage:

Length of incline / Height of inclineLength of incline / Height of incline Example: RampExample: Ramp

WedgeWedge Two Inclined Planes, Two Inclined Planes,

Back to BackBack to Back Thick at one end, tapers Thick at one end, tapers

to thin edge = strong to thin edge = strong output forceoutput force

Example: Axe, Knife, Example: Axe, Knife, Splitting wedge, zipperSplitting wedge, zipper

ScrewsScrews

Inclined Plane wrapped Inclined Plane wrapped around a cylinderaround a cylinder

Applies input force over Applies input force over a long distancea long distance

Closer the threads, Closer the threads, greater advantagegreater advantage

Examples: Screws, jar Examples: Screws, jar lids, faucetslids, faucets

LeversLevers Rigid Bar that pivots on a fixed object (the Rigid Bar that pivots on a fixed object (the

fulcrum)fulcrum) Mechanical Advantage of lever:Mechanical Advantage of lever:

Distance from fulcrum to input force / Distance Distance from fulcrum to input force / Distance from fulcrum to output forcefrom fulcrum to output force

Three classes of levers:Three classes of levers: First Class: fulcrum between input & output (pry First Class: fulcrum between input & output (pry

bar)bar) 22ndnd Class: Output between input and fulcrum Class: Output between input and fulcrum

(Wheelbarrow)(Wheelbarrow) 33rdrd Class: Input between output and fulcrum Class: Input between output and fulcrum

(Rake)(Rake)

First Class LeverFirst Class Lever

Second Class LeverSecond Class Lever

Third Class LeverThird Class Lever

Wheel and AxleWheel and Axle

Two cylindrical objects that Two cylindrical objects that rotate around a common axisrotate around a common axis Larger is wheelLarger is wheel Smaller is axleSmaller is axle

Advantage: Multiplies force Advantage: Multiplies force over longer distanceover longer distance Radius of Wheel / Radius of AxleRadius of Wheel / Radius of Axle

PulleyPulley A grooved wheel with a ropeA grooved wheel with a rope Pulley used to change directionsPulley used to change directions Fixed Pulley: pulley attached to a structure Fixed Pulley: pulley attached to a structure

(advantage = 1)(advantage = 1) Movable Pulley: pulley attached to object Movable Pulley: pulley attached to object

you wish to pull (advantage = 2)you wish to pull (advantage = 2) Pulley Systems: (block and tackle) Pulley Systems: (block and tackle)

combination of fixed and moveable pulleyscombination of fixed and moveable pulleysAdvantage = number of sections of ropeAdvantage = number of sections of rope

Single PulleySingle Pulley

Let’s Look at how to lift a large object:

•100 lb block of something.•We could lift it with a rope•To lift it 10 meters in 1

second would take 454N of force

•To lift 10 meters would take 454J of work

Single PulleySingle PulleyIf we add a single pulley to

the system by running a rope over a wheel:

•We could lift it with a rope•To lift it 10 meters in 1

second would take 454N of force

•To lift 10 meters would take 454J of work

•But now we are pulling DOWN or sideways instead of up – usually easier•Gravity works with us instead of against us

2 Pulleys – a Pulley System2 Pulleys – a Pulley System

You can see that the weight is now suspended by two pulleys rather than one.

• That means the weight is split equally between the two pulleys,

• each one holds only half the weight, or 50 pounds (22.7 kilograms).

• you only have to apply 50 pounds of force (the ceiling exerts the other 50 pounds of force on the other end of the rope).

• Mechanical advantage is now 2 (2 output force for 1 input force)

Pulley Systems – Block and TacklePulley Systems – Block and Tackle

In this diagram, the pulley attached to the weight actually consists of two separate pulleys on the same shaft, as shown on the right. This arrangement cuts the force in half and doubles the distance again. To hold the weight in the air you must apply only 25 pounds of force, but to lift the weight 100 feet higher in the air you must now reel in 400 feet of rope.

• Mechanical Advantage depends on number of loops around the pulley

• 4 Loops = 4/1 advantage

Compound MachinesCompound Machines

Complex Machines Complex Machines Use two of more simple Use two of more simple

machinesmachines Example: pencil Example: pencil

sharpener uses wheel sharpener uses wheel and axle to turn inside and axle to turn inside mechanism. Inside, axle mechanism. Inside, axle turns gears, which turn turns gears, which turn two cutting screws two cutting screws (screw + wedge) cut (screw + wedge) cut wood. wood.

GEARS: link one wheel GEARS: link one wheel & axle to another& axle to another