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# Do Now 3 /3/2014 - PowerPoint PPT Presentation

Do Now 3 /3/2014. Take 4 sheets from back table Homework – Simple Machine worksheet Test Thursday. Simple Machines. Levers. A lever is a rigid bar that is free to pivot, or rotate, about a fixed point. The fixed point that a lever pivots around is called the fulcrum . .

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Do Now 3/3/2014

• Take 4 sheets from back table

• Homework – Simple Machine worksheet

• Test Thursday

### Simple Machines

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

• The fixed point that a lever pivots around is called the fulcrum.

• I.M.A=

Distance from fulcrum to input force

Distance from fulcrum to output force

Output force

First Class Lever

• The Fulcrum (fixed pivot point) is located between the Input and the Output Forces.  A SEESAW.

• The Input and the Output Forces move in opposite directions.  The Input Down in order to Lift the Load.

• When the Fulcrum is closer to the Input than to the Output, there is a Loss in Force but a Gain in Speed and Distance.

• When the Fulcrum is closer to the Output than to the Input, there is a Loss in Speed and Distance, but a Gain in Force.

• When the fulcrum is Midway between the Input and the Output, there is no change in Force, Speed or Distance.

• Samples of First Class Levers – Seesaw, Crowbars, Scissors, and Claw Hammers.

Input force

Second Class Lever

• The Output Force is between the Input Force and the Fulcrum.

• The Fulcrum is at one End of the Lever.

• The Fulcrum is usually closer to the Output Force, (load).

• Second Class Levers produce a gain in Force.

• Samples of Second Class Levers – Wheelbarrow, Bottle Openers, and NutCrackers.

Input force

Output force

Output force

Input force

Input force

Output force

• The Input Force is Between the Output force and the Fulcrum.

• Samples of Third Class Levers – Broom, Shovel, Fishing Pole, Baseball Bat, and Tongs.

• A grooved wheel with a rope (or a chain, or even steel cable) wrapped around it.

• You can change the direction and the amount of your input force.

• A pulley that you attach to a structure.

• Changes the direction of the input force.

• Does not change the amount of force you apply.

• Ideal Mechanical Advantage = 1

1

• If you attach a pulley to the object that you wish to move.

• I.M.A= 2

• The output force is 2 times the input force you exert on the rope.

• You must exert your force over a greater distance.

2

• The ideal mechanical advantage of a pulley system is equal to the number of sections of rope that support the object.

1

1

2

2

b

c

Efficiency?

b

A

b

b

• Two or more wheels linked together by interlocking teeth.

• A machine that utilizes two or more simple machines.