What is a machine?

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What is a machine?

• A machine is a device that makes work easier by
  changing
• the amount of force you exert,
• the distance over which you exert your force, or
• the direction in which you exert your force.

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Work In, Work Out
When you use a machine you do work on
the machine (input or effort force), and the
machine does work on something else (output or
resistance force).
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Machines do not save work!
Remember Work Force x Distance
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When a machine changes the size of the force, the
distance through which the force is exerted must
also change.
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Work input Machine Work
output Example
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Work input Machine Work output
Example
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Work input Machine Work
output Example
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Window blinds do not multiply force, they change
the direction of the effort force. Pulling
down on the cord changes the direction of the
force to pull the blinds up. Effort force and
resistance force are equal. Mechanical advantage
is 1
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What is Mechanical Advantage?

• Mechanical advantage is a number that tells how
  many times a machine multiplies force.
• Mechanical advantage (MA)
• output force (Resistance)
• input force (Effort)

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MA 500 N 10 50 N
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What is a lever?

• A lever is a rigid bar that is free to pivot, or
  rotate, about a fixed point (fulcrum).

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First class levers
Can be used to increase force or to
increase distance.
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Second class levers
Second class levers do not change the direction
of the input force, but allow you to apply less
force than the force exerted by the load.
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Third class levers
Do not change the direction of the input force
and do not increase the input force. Output
force is always less than the input force.
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Mechanical Advantage of levers.
Ideal mechanical Distance from fulcrum to
input force advantage
Distance from fulcrum to output force.
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1st Class Levers
Different classes of levers are identified by the
way the joint and muscles attached to the bone
are arranged. For the Class 1 lever the pivot
lies between the effort and load. A see saw in a
playground is an example of a Class 1 lever where
the effort balances the load. This pivot exists
in the place where your skull meets the top of
your spine. Your skull is the lever arm and the
neck muscles at the back of the skull provide the
force (effort) to lift your head up against the
weight of the head (load). When the neck muscles
relax, your head nods forward.
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dge/sci_media/images/tip_toe
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2nd Class Lever
Different classes of levers are identified by the
way the joint and muscles attached to the bone
are arranged. For the Class 2 lever the load is
between the pivot and the effort (like a
wheelbarrow). The effort force needed is less
than the load force, so there is a mechanical
advantage. Standing on tip toes is a Class 2
lever. The pivot is at your toe joints and your
foot acts as a lever arm. Your calf muscles and
achilles tendon provide the effort when the calf
muscle contracts. The load is your body weight
and is lifted by the effort (muscle contraction).
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3rd Class Lever
Different classes of levers are identified by the
way the joint and muscles attached to the bone
are arranged. For a Class 3 lever the load is
further away from the pivot than the effort.
There is no mechanical advantage because the
effort is greater than the load. However this
disadvantage is compensated with a larger
movement. This type of lever system also gives us
the advantage of a much greater speed of
movement. A bent arm is a Class 3 lever. The
pivot is at the elbow and the forearm acts as the
lever arm. The biceps muscle provides the effort
(force) and bends the forearm against the weight
of the forearm and any weight that the hand might
be holding.
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Different classes of levers are identified by the
way the joint and muscles attached to the bone
are arranged. For a Class 1 lever the pivot lies
between the effort and the load. A see saw in a
playground is an example of a Class 1 lever where
the effort balances the load. The place where
your skull meets the top of your spine is a Class
1 lever. Your skull is the lever arm and the neck
muscles at the back of the skull provide the
force (effort) to lift your head up against the
weight of the head (load). When the neck muscles
relax, your head nods forward.
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Different classes of levers are identified by the
way the joint and muscles attached to the bone
are arranged. For the Class 2 lever the load is
between the pivot and the effort (like a
wheelbarrow). The effort force needed is less
than the load force, so there is a mechanical
advantage. Standing on tip toes is a Class 2
lever. The pivot is at your toe joints and your
foot acts as a lever arm. Your calf muscles and
achilles tendon provide the effort when the calf
muscle contracts. The load is your body weight
and is lifted by the effort (muscle contraction).
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Different classes of levers are identified by the
way the joint and muscles attached to the bone
are arranged. For a Class 3 lever the load is
further away from the pivot than the effort.
There is no mechanical advantage because the
effort is greater than the load. However this
disadvantage is compensated with a larger
movement. This type of lever system also gives us
the advantage of a much greater speed of
movement. A bent arm is a Class 3 lever. The
pivot is at the elbow and the forearm acts as the
lever arm. The biceps muscle provides the effort
(force) and bends the forearm against the weight
of the forearm and any weight that the hand might
be holding.
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