Mechanical Advantage

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Mechanical Advantage Simple Machines (esp.
Levers!)
Making Work Feel Easier!
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1 Revisiting Work
We know that WORK is done when a force moves an
object a distanceits calculated by multiplying
the forces strength by the distance the object
moves.
W F x d
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2 Yeah, we know thatweve done a billion of
those problems
but did you stop to realize that theres almost
always a way to make the same amount of work
easier???
Heres Joes TV
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3 Joe wants his TV on top of his dresser
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4 So Joe does what people have done for
thousands of years
_at_!
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5 He finally does itwhat has he accomplished
(besides a sore back)?
W F x d W 300N x 1.5m W 450 J
TV 300 N
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6 Joes uncle, a professional mover, gives him a
tip on the phone
Use a Ramp Next Time!
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7 What if he HAD used a ramp???
Joe pushes with 150N
W F x d W 150N x 3m W 450 J
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8 Lets compare the 2 methods
Pick up TV
Use a ramp

• Distance 1.5 meters (short)
• ?

• Distance 3 meters (longer)
• ?

• Force 150N (not so bad)
• ? ?

• Force 300N (HEAVY)
• ? ? ?

• Work done 450J

• Work done 450J

I know which one I'd pick, especially if I had 20
TVs!
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9 So, using a ramp is better?
Well, it is in situations where you want to make
things feel lighter than they really are. A ramp
is just one kind of simple machine
Simple machine a device that makes work feel
easier by reducing the amount of force needed to
move an object.
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10 Six simple machines

• Lever

• Pulley

These things all make work feel easier. How? By
making the force you have to push or pull with a
lot less than just picking things straight
up. Yes, you push/pull farther, but who cares if
it lets you get the job done?

• Inclined plane (ramp)

• Screw

• Wheel Axle

• Wedge

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11 Thank you for
Considering the following
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12 Lets talk about Levers

• Levers have 3 parts
• Load object lifted or moved
• Fulcrum pivot point
• Force your push or pull

Force
Load
Fulcrum
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13 Three kinds of levers
Three classes of levers depend on which of the 3
parts is in the middle.
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14 How is the 2nd class different?
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15 and the 3rd class lever?
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16 How to tell which class a lever is

• 1. Identify the three parts of the lever
• Force (where you grab use the lever)
• Fulcrum (where it pivots)
• Load (the object raised, moved, crushed, etc.)
• 2. Decide which part is in the middlethat lets
  you know.

Fulcrums in the middlethis is a 1st class lever
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17 How does a lever help?
Your job is to get this 100N weight onto the
table. If you picked it straight up, the force
(100N) and distance (1m) would be 100J.
100 N
Using this lever, you will pull a lot farther
(2.5m), but the ball will feel like its only
40N. The total work is still 100J, the same as
picking it up, but it feels a whole lot easier!
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18 This concept is called
Mechanical advantage the amount that a simple
machine reduces the force needed to do work.
Mechanical Advantage
Example A lever makes a 60 pound dog feel like
its only 20 pounds. Whats this levers
mechanical advantage?
60 lbs. 20 lbs. 3 This lever will make
anything feel 3 times lighter than it really is.
A 108 pound teenager would feel like 36 pounds
(divide by 3) using this lever!
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19 More with Mechanical Advantage

• We will abbreviate mechanical advantage with
  M.A.
• M.A. has no units. Its just a number.
• The true weight of the object is called Output
• Force, abbreviated Fo
• The force you have to push/pull with is called
• Input Force, Fi

(we just need some practice)
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20 Levers have their own trick to finding
Mechanical Advantage
If you know how far it is from the fulcrum to
your force, and also how far it is from the
fulcrum to the load, just divide the two.
MAlever (distance fulcrum to force) (distance
fulcrum to load)
This levers MA is 9. It makes things feel 9
times lighter!
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21 Summary

• If youd rather push a light object a longer
  distance RATHER than
• break your back by picking up a heavy object,
  then use a simple
• machine. SIMPLE MACHINES MAKE WORK FEEL EASIER.
• Levers come in 3 varietiesthese classes depend
  on which of the
• 3 parts is in the middle.
• Levers, like the other simple machines, use a
  concept called
• mechanical advantage (MA) to increase the
  distance you push,
• while reducing how hard you have to push.
• MA is a number showing how many times easier work
  feels when
• using a simple machine. A pulley with MA of 5
  would make a
• 40 pound kid feel like 8 pounds. Nice!

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22 And thats the