Simple%20Machines%20and%20Mechanical%20Advantage

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Simple Machines and Mechanical Advantage

• Machine is an instrument that makes work EASIER.

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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.
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Rube Goldberg
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Honda Commercial
http//www.boardsmag.com/screeningroom/commercials
/581
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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
• Effort Force is the force applied TO the
  machine. (usually what YOU apply to the machine)
• Effort Distance is the distance over which you
  apply force.

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Simple Machines and Work

• 2. Work Output the work done by the MACHINE
• WORK OUTPUT Resistance Force X Resistance
  Distance
• Resistance Force is usually the weight of the
  object being moved.
• Resistance Distance is the distance the object is
  moved EVEN if there was no machine.

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IMPORTANT!

• Machines DO NOT INCREASE the work put into them,
  they just make work easier.
• Allows you to use
• less force!!!

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Mechanical Advantage

• Mechanical Advantage how many times the machine
  multiplies your effort force.
• how much the machine REDUCES how much effort
  force you have to apply.
• What you lose in EFFORT FORCE, you gain in EFFORT
  DISTANCE.

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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.
• This allows you to REDUCE the EFFORT FORCE needed
  by 2.5 times.

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Mechanical Advantage

• Ideal Mechanical Advantage (IMA)
• Assumes that there is NO FRICTION involved.
• IMA Effort Distance/ Resistance Distance
• or
• Resistance Force/ Effort Force
• Ed / Rd or Rf / Ef

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6 Types of Simple Machines

1. Inclined Plane
2. Wedge
3. Screw
4. Lever
5. Wheel and Axle
6. Pulley

All are forms of inclined planes
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Inclined Plane

• A flat slanted surface

Ef
Rf
Rd
Ed
The weight of the box is the Rf
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Inclined Plane IMA
Ed
IMA Ed / Rd 3m / 1.5m 2 or IMA Rf /
Ef 250/ ???
Rf
IMA
Rd
IMA
Ef
Box weighs 250 N
3 meters
1.5 meter
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Inclined Plane and Work

• Work Force X Distance
• Use either Resistance Force and Resistance
  Distance
• OR
• Effort Force and Effort Distance

Box weighs 250 N
3 meters
1.5 meter
Work Rf x Rd 250 N X 1.5m 375
Joules
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Wedge

• A moving inclined plane

The longer and thinner the Wedge (inclined
plane), the higher The IMA. (the better the
machine)
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IMA of a Wedge
6 cm
6 cm
A wedge is 2 inclined Planes together.
10/6 1.67 10/6 1.67 _______
3.34
Ed/ Rd
10 cm
10 cm
Calculate the IMA of each Inclined plane and
add together.
IMA is 3.34
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Screw

• An inclined plane wrapped around a central bar to
  form a spiral

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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.
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Lever

• Rigid bar that is free to pivot about a fixed
  point.
• Fulcrum the fixed point on a lever.

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Classes of Levers
force
Rf
________
Rf
1st Class F 2nd Class R 3rd Class E
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

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1st Class Lever
Ef
Ef
Ef
Rf
Rf
Rf
Changes direction of the force
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2nd Class Lever
Rf
Ef
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3rd Class Lever
Does not multiply your effort force, It just
makes it a little easier (or increases speed)
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Levers and IMA
What is the IMA of the following lever? What
kind of lever is it?
.25 m
Ef
2 m
300 N
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Levers and IMA
What is the IMA of the hockey stick? What
type of lever is the hockey stick?
Ef 60 N
. 5 m
2.5 m
Rf
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Wheel and Axle

• Made up of 2 circular
• objects of different sizes

• Wheel the large circle
• Effort distance

• Axle the smaller circle.
• Resistance Distance

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Wheel and Axle
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Wheel and Axle and IMA
What is the IMA? Ed/Rd
6 cm
24 cm
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Pulley

• A rope, belt or chain wrapped around a
• grooved wheel.

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Type of Pulleys

• Fixed Pulley pulley attached to a structure.
• Changes the direction of the Effort Force
• DOES NOT multiply your effort force

• Calculate IMA by counting the
• number of SUPPORTING ropes.

IMA 1
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Types of Pulleys

• Movable Pulley attach pulley to a moving object

• Multiplies force, but does not change direction

IMA 2
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Compound Pulleys

• Combination fixed and movable pulleys

IMA
IMA
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Examples of Pulleys
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Examples
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Block and Tackle System
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I guess thats It! Whew!

• Any Questions?