January 4, 2010

• Quietly get out Problem Set 2 Solutions (classwork/ homework) for a review today.

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DRILL

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F x d = W

Wo / Wi = Eff

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• The technology of putting together mechanical parts to produce, control, and transmit motion.

Example applications: •Gear systems in a car transmission, •Brakes on a bicycle, •Agitator in a washing machine, •Latch on a door.•Springs in vehicle shocks

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• Machines are artifacts that transmit or change the application of power, force, or motion.

• What is an artifact?– something created by humans usually for a practical

purpose.

• Machines can be simple or complex– Complex machines are comprised of….

• Inputs go in• Outputs come out

Simple Machines

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1.COMPONENTS:– Levers

– Pivot Points

– Linkage Joints

INPUT

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• INSTRUCTIONS: Transmit the given input motion to the desired output motion using only the allowed components.

input input input

input input

2. 3. 4.

5. 6.

• Correctly copy the following onto the remaining 2” x 2” boxes in your notebook.

1. A hot air balloon carries 200 lbs cargo, 150 lbs human, and 200 lbs materials up a distance of 2,000 feet. How much work did the balloon do (keep all units)?

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2. A physical therapy doctor told his 150-lb patient to do 30,000 ft-lbs of work each day to rehabilitate his leg. The patient decides to climb a hill to perform this work. How high does the patient need to climb in order to meet his goal?

1. F x d = W

550 lbs x 2,000 ft =

W = 1,100,000 ft-lbs.

2. F x d = W

150 lbs x d = 30,000 ft-lbs.150 lbs. 150 lbs.

d = 200 ft.

1. You have a dog that weighs 50 pounds. You carry her up the stairs a total vertical height of 9 feet. How much work did you do (keep all units)?

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2. 2004 Hummer H2

• Output = 320 miles• Input = 32 gallons• Efficiency = ?

3. 2004 Toyota Prius

• Output = 500 miles• Input = 10 gallons• Efficiency = ?

F x d = W

50 lbs x 9 ft =

W = 450 ft-lbs.

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DRILL (continued)

2. 2004 Hummer H2

• Output = 320 miles• Input = 32 gallons• Efficiency = ?

3. 2004 Toyota Prius

• Output = 500 miles• Input = 10 gallons• Efficiency = ?

Wo / Wi = Eff

320 mls / 32 gal =

Eff = 10 mpg

Wo / Wi = Eff

500 mls / 10 gal =

Eff = 50 mpg

Identify which Core technology is represented by the examples below:

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a. Door latch e. Crankshaft

b. Thermostat f. Cylinder

c. Fan g. Battery

d. Light bulb h. Gas tank

a. Mechanical

b. Electronic

c. Mechanical/Thermal

d. Optical

e. Mechanical

f. Structural

g. Electrical

h. Structural

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• 3 Categories of simple machines based on the principle of the LEVER:

LEVER

Lever Wheel and Axle

Pulley

• Lever Arm • Fulcrum• Applied Force• Load• 3 different Classes of levers:

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LEVER

Which is 1st class?

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• 1st class:– The fulcrum is between the load and the effort force

LEVER

Which is 2nd class?

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• 2nd class:– The load is between the effort and the fulcrum

LEVER

Which is 3rd class?

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• 3rd class:– The effort is placed between the load and the fulcrum

LEVER

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• Notice the direction of motion of the Force and Load for each of the 3 classes of lever.

Sketch the pictures below and answer the questions:

• Which lever would be easier to push down, A or B?

• Which load will travel the greater distance, A or B?

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A B

Demonstrate it

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• Simple machines work on 2 basic principles:

LEVER

INCLINED PLANE

Principle: a law of nature underlying the working of an artificial device

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• Which class is the lever below?• Describe it.

FIRST CLASSSECOND CLASSTHIRD CLASS

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• A shaft attached to a disk

WHEEL-and-AXLE

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• Which class of lever?

WHEEL-and-AXLE

2nd Class

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• Which class of lever?

WHEEL-and-AXLE

3rd Class

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• Pulleys are grooved wheels attached to an axle.• Generally, what class lever do they act as?

PULLEYS

1st Class

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• Simple Machines can be:

– Force Multiplier: Increases the force applied to the work at hand

– Distance Multiplier: Increases the distance the load moves

FORCE/DISTANCE MULTIPLIERS

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• From the drill:– Which is the force multiplier?

• In other words, which arrangement gives you greater strength

FORCE/DISTANCE MULTIPLIERS

A B

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• From the drill:– Which is the distance multiplier?

• In other words, which arrangement gives you greater distance

FORCE/DISTANCE MULTIPLIERS

A B

MECHANICAL ADVANTAGE

FORCE MULTIPLIERS

FL

DL DF

For All Lever Classes

What are the units for MA?There are no units – it’s a ratio

DFDL

M.A.= LF

=

MA is the number of times a mechanical device multiplies

the Applied Force

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You now have 2 equations:

L x DL = F x DF

DF L

DL F

FORCE MULTIPLIERS

=

Hint: They’re really the same equation rearranged

• Machines are… – artifacts that transmit or change the application of power,

force, or motion.

• What is an artifact?– something created by humans usually for a practical

purpose.

• Machines can be simple or complex– Complex machines are comprised of…. Simple Machines

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M.A. = Radius (D) to Force (F) = DF

Radius (D) to Load (L) DL

• Rotary Motion • the circular motion which occurs when the wheel and

axle are rotated about the centerline axis. • Linear Motion

• the straight-line motion which occurs when a wheel rolls along a flat surface. The linear distance traveled when the wheel completes one revolution is equal to the circumference of the wheel.

Circumference = Pi * Wheel diameter U3d-L8

WHEEL AND AXLE

• A pulley is an adaptation of a wheel and axle.

• A single pulley simply reverses the direction of a force.

• When two or more pulleys are connected together, they permit a heavy load to be lifted with less force.

• The trade-off is that the end of the rope must move a greater distance than the load.

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PULLEY

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M.A. = Total number of strands supporting the load

MA = L / F

PULLEY

• Fixed Pulley – when a pulley is attached or fixed to a strong member, which will not move.

• How many strands are supporting the load?

• What is the MA of a fixed pulley?

• How many lbs of force are required to lift 100 lbs of load?

• When a fixed pulley is used, the force needed to lift a weight does not change.

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11

100

PULLEY

• Movable Pulley – splits the work in half.• How many strands are supporting the load?• What is the MA of a movable pulley?• How many lbs of force are required to lift 100 lbs of load?• When a movable pulley is used, the force needed to lift a

load is half that of the load.

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2

50

2

PULLEY

• Block and Tackle – a system of three pulleys• How many strands are supporting the load?• What is the MA of a movable pulley?• How many lbs of force are required to lift 120 lbs of load?• When a block and tackle is used, the force needed to lift a

load is 1/3 that of the load.

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40

33

PULLEY

• 3 Categories of simple machines based on the principle of the INCLINED PLANE:

INCLINED PLANE

Inclined Plane Wedge Screw

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• Inclined Plane – sloped surfaces used to make a job easier– Easier to go up a slope than a vertical surface

• Wedge – used to split, separate, and grip– Wood chisel, firewood axe, doorstop

• Screw – an inclined plane wrapped around a shaft– 1/2-inch x 12 machine screw

• ½” diameter• 12 threads per inch

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• The inclined plane is the simplest machine of all the machines.

• An inclined plane is a flat sloping surface along which an object can be pushed or pulled. An incline plane is used to move an object upward to a higher position.

H

D

L

F

M.A.= Distance = D

Height H

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Effort

Wedge -Comparison to the Inclined Plane

Inclined Plane

Effort

Wedge

Wedges can be single or double:

Single Double

L

H

L

H

FORCE

Effort

Wedge -Comparison to the Inclined Plane

Inclined Plane

Effort

Wedge

Wedges can be single or double:

Single Double

L

H

L

H

FORCE

1. During its use, an inclined plane remains stationary, while the wedge moves.

2. With an inclined plane the effort force is applied parallel to the slope of the incline.

3. With a wedge the effort force is applied to the vertical edge (height) incline.

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D

HM.A.=

Effort

Wedge -Comparison to the Inclined Plane

Inclined Plane

Effort

Wedge

Wedges can be single or double:

Single Double

L

H

L

H

FORCE FORCE

DD

H H