Machines, Work and Energy

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Machines, Work and Energy

• When someone does work what does that
  m-e-a-n???

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Is this weightlifter doing work??
NO!!
But But But But Hes trying to lift 832 pounds!!!
So hes definitely exerting a force.
Then why isnt he doing work??
The weights DID NOT MOVE.
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In science, work is calculated using a formula
(of course)

• Work Force X Distance
• Force units Newton, N
• Distance units meter, m
• Work units Joule, J
• J Nm

OHHHH, Now I get it The weightlifter was
applying a BIG force, but if the object doesnt
move, then distance zero. And anything times
zero is
ZERO
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Some work is too hard to do by ourselves. (Even
if you are a weighlifter.)
What can we use to help us??
MACHINES!!

• Change the amount of force you exert
• Change the distance over which you exert force
• Change the direction in which you exert force
• But machines DO NOT change the amount of work done

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What is a machine?

• a tool that enables you to do work.
• works by changing the direction or size of the
  force needed to do the work.

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SIMPLE MACHINES

• A machine that does work with one movement.
• There are six simple machines.

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INCLINED PLANE

• A sloped or slanted surface that is used to raise
  or lower an object.
• An inclined plane reduces the effort force
  needed.
• You gain mechanical advantage by

MA length of plane height of plane
2 meters
10 meters
What is the mechanical advantage?
MA 10 m 2 m
MA 5
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SCREWS

• The screw is an inclined plane wrapped around a
  cylinder.

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A screw

• is a curving inclined plane.
• is used to
• fasten,
• lift, or
• apply pressure.

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Wedge is defined as an

• Inclined plane that
• Moves and
• Is used to cut or separate
• The wedge may consist of

a Single inclined plane

• or
• Two inclined planes
• back to back.

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A lever

• is a bar that rests or turns on a fulcrum.
• makes it easier to lift a weight.

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LEVERS

• A lever is a rod or a bar which moves around a
  fixed point called a fulcrum.
• The fulcrum is the fixed point about which the
  lever pivots.
• Levers are classified according to the locations
  of
• Effort force (where you are applying the effort).
• Resistance force (what you are trying to move).
• And the fulcrum
• There are three classes of levers.

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1st CLASS LEVERS

• The fulcrum is located between the effort force
  and the resistance force.
• Effort is applied to one end of the lever, and
  the resistance is moved in the opposite direction.

Resistance force
Effort force
Fulcrum
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2nd CLASS LEVERS
Resistance force

• The resistance is located between the fulcrum
  and resistance force.
• An example of a 2nd class lever is a

Door
Effort force
Fulcrum
Bottle opener
Wheel barrow
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3rd CLASS LEVERS
Fulcrum

• In the third class lever, the effort is located
  between the resistance arm and the fulcrum.
• Examples of a third class lever are

Effort force
Resistance force
Raking
Fishing
Playing baseball Or golfing!
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MECHANICAL ADVANTAGEOF LEVERS
Effort force

• The mechanical advantage (MA) of a lever is
  measured by
• M A effort arm length
• resistance arm length

4m
Resistance force
2m
What is the MA of the Lever???
MA EAL RAL
Fulcrum
MA 4m 2m
MA 2
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A pulley

• is made up of
• a wheel,
• an axle, and
• a rope.
• makes it easier to lift heavy objects.

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PULLEYS

• A pulley is a wheel with a rope, belt, or chain
  wrapped around it.
• There are fixed pulleys, and moveable pulleys.
• There are also pulley systems, or more than 1
  pulley working together to move an object.

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FIXED PULLEYS
Pulley attached to Stationary object.

• The mechanical advantage of a fixed pulley is 1.
• The fixed pulley only changes the direction of
  the effort force.
• Effort force must be greater than resistance
  force for the object to move.
• A pulley gains advantage by the distance the rope
  is pulled.

Rope
Resistance force
Effort force
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MOVEABLE PULLEYS
Effort force

• A moveable pulley moves with the resistance as
  you pull on the rope.
• The MA of a moveable pulley is greater than 1
  because it multiplies the effort force.
• The distance that you pull the rope, will
  however, be further than the object moves.

Rope
Moveable pulley
Resistance Force
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A wheel and axle

• is a larger wheel connected to a smaller inner
  one.
• is used to
• turn objects, or
• move objects across a surface.

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WHEEL AND AXLE

• A wheel attached to a shaft which is called an
  axle.
• The mechanical advantage is a ratio of the size
  of the wheel in comparison to the size of the
  shaft.

Wheel is 15cm in diameter, and the shaft is 2cm
in diameter. What is the mechanical advantage?
MA wheel radius radius of axle
MA 15cm 2cm

MA 7.5
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Pulleys
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If you needed to move a heavy rock, you would use
me. (Hint I have a fulcrum.)
Now for a review

• I am a lever.

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You need to move a piano into a truck in the
easiest way possible. Which simple machine would
you use?

• You would use an inclined plane.

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If you wanted a bucket of water from a well, I
would come in handy. What simple machine am I?

• I am a pulley.

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When youre riding your bicycle, I am the simple
machine that moves along the surface on which you
are riding. What am I?

• I am a wheel and axle.

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When you want to keep your door from slamming
shut, which simple machine would you use?

• You would use a wedge.

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COMPOUND MACHINES

• A machine with two or more simple machines
  working together.
• Almost everything we use is a compound machine.
• Do not confuse compound machine with complex!
• A pair of scissors and a pencil sharpener are
  examples of compound machines.