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1
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2
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3
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- Work is done when a force causes an object to move in the direction that
the force is applied.
- The formula for work is: W = F X D
- If there is no movement, there is no work
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4
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5
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- A force must applied to an object
- The object must move in the same direction as the force.
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6
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7
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8
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9
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- They can change the amount of force
- They can change the distance
- (Remember that Work = Force X Distance)
- They can also change the direction
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10
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- Any change in the size of the force changes the distance. No machine can
increase both force and distance.
- Multiply force which decreases distance the load moves.
- Multiply the distance which decreases force.
- Or, they leave force and distance alone but change the direction in
which the load moves.
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11
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12
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- The number of times a machine multiplies the effort or input force.
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13
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14
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- There are three simple machines:
- The lever, the pulley, and the inclined plane
The wheel and axle, the wedge, and the screw are modifications of
these simple machines.
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15
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16
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- A machine made up of two or more
simple machines.
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17
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18
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- A simple machine made with a rigid bar free to pivot (move) around a fixed point
called a fulcrum
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19
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20
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- A first class lever is like a teeter-totter or see-saw. One end will
lift an object (child) up just as far as the other end is pushed down.
- A second class lever is like a wheel barrow. The long handles of a wheel
barrow are really the long arms of a lever.
- A third class lever is like a fishing pole. When the pole is given a
tug, one end stays still but the other end flips in the air catching the
fish.
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21
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22
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23
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24
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- A simple machine made with a rope, belt or chain wrapped around a
grooved wheel. A pulley works two ways.
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25
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26
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27
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- A pulley works two ways.
- It can change the direction of a force or it can change the amount of
force.
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28
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29
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- Fixed pulley
- Does not multiply force.
- Changes the direction of the effort force.
- Mechanical advantage is equal to one.
- Movable pulley
- Multiplies effort force but cannot change direction of the effort
force.
- Mechanical advantage is the effort distance divided by the resistance
distance.
- Pulley system
- A combination of fixed and movable pulleys.
- Mechanical advantage is equal to the number of supporting ropes.
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30
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31
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- A fixed pulley changes the direction of the applied force. ( Ex. Raising
a flag )
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32
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33
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- A movable pulley is attached to the object that is being moved.
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34
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35
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- A simple machine with no moving parts. It is simply a straight slanted
surface. ( Ex. a ramp.)
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36
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37
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38
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- A wheel and axle is a modification of a pulley. A wheel is fixed to a
axle.
- The wheel and axle must move together to be a simple machine.
- Sometimes the wheel has a crank or handle on it.
- Examples of wheel and axles include roller skates and doorknobs.
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39
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40
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41
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- A modification of an inclined plane that moves .
- It is made of two inclined planes put together.
- Instead of the load being moved up an inclined plane, the inclined plane
moves the load.
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42
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43
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44
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- A simple machine that is like an inclined plane.
- It is an inclined plane that wraps around a shaft.
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45
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46
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- http://www.usoe.k12.ut.us/curr/science/sciber00/8th/machines/sciber/intro.htm
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Notes
