simple machines making life easier through physics
TRANSCRIPT
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Simple Machines
Making Life Easier Through Physics
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Work and Energy• Energy is conserved – you
can’t create it or destroy it
• Work is transferring energy from one object to another
• Simple machines can’t increase or decrease the amount of work you do
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Calculating Work
• Work doesn’t change when you use a machine• Most simple machines make our lives easier
by DECREASING the amount of force we need to apply to finish a job – If you decrease the force, the distance must
increase
• Some DSECREASE the distance instead– If you decrease the distance, the force must
increase
dFW
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Types of Simple Machines
•Lever Family–Lever–Pulley–Wheel and axle
•Inclined Plane Family–Inclined plane–Wedge–screw
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Lever• Rigid arm with a turning
point• Turning point is called the
fulcrum• Moves force to a new
location– Resistance force is the force
the lever applies to an object– Effort force is the force a
person applies to the lever• Three classes of levers
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1st class levers• Effort force and
resistance force are on opposite sides of the fulcrum
• Seesaws are a first class lever
fulcrum
Effort force Resistance force
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2nd class levers• Resistance force is
between the fulcrum and the effort force
• wheelbarrows are a second class lever
fulcrum
Effort forceResistance force
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3rd class levers• Effort force is
between the resistance force and the fulcrum
• Your biceps are a third class lever
fulcrum
Effort force Resistance force
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Wrap-Up #1• Classify the following levers by
class1. Scissors2. Fishing rod3. Stapler
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Wrap-Up #1: Answers• Classify the following levers by class1. Scissors
1st class – handle has effort force, the joint is the fulcrum and the blades apply the resistance force
2. Fishing rod3rd class – fulcrum by your body, handle has effort force and the line has the resistance force
3. Stapler 2nd class – the pivot is the fulcrum, you push in the middle and the staple is the resistance force
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Pulleys• The middle point is
like the fulcrum of a lever
• Mechanical advantage is equal to number of ropes
• Three kinds– Fixed pulley– Movable pulley– Block and tackle
(multiple pulleys at the same time)
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Wheel and Axle•Pulley (wheel)
connected to a shaft (axle)
•Small force on the large wheel is turned into a bigger force on the smaller axle
•Screwdrivers are also wheel and axles
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Inclined Plane• Allow you to apply
a horizontal force to move things up
• You use less force than if you lift straight up
• You apply the force over a longer distance, so the work doesn’t change
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Wedge• Changes the direction
of the force and splits it into two– If you push down the
wedge pushes to the left and right
• Useful for splitting things like firewood and your food
• Nails are wedges used to hold things together instead
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Screw• An inclined plane
wrapped around a cylinder
• Allows you to twist it into place instead of pushing straight down
• Allows a longer plane than if it was straight (spiral staircase)
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Wrap-Up #2• Classify each of these images as a type
of simple machine
#1
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Wrap-Up #2• Classify each of these images as a type of simple machine
SCREW
• Classify each of these images as a type of simple machine
#1
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Wrap-Up #2• Classify each of these images as a type
of simple machine
#2
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Wrap-Up #2• Classify each of these images as a type of simple machine
INCLINED PLANE
• Classify each of these images as a type of simple machine
#2
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Wrap-Up #2• Classify each of these images as a type
of simple machine
#3
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Wrap-Up #2• Classify each of these images as a type of simple machine
PULLEY
• Classify each of these images as a type of simple machine
#3
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Wrap-Up #2• Classify each of these images as a type
of simple machine
#4
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Wrap-Up #2• Classify each of these images as a type of simple machine
LEVER
• Classify each of these images as a type of simple machine
#4
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Mechanical Advantage• A measure of how
much the machine helps you– MA < 1, you apply a
stronger force over a smaller distance
– MA = 1, the force’s direction is changed
– MA > 1, you apply a lower force over a greater distance R
E
E
R
d
d
F
FIMA
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Efficiency• Some energy
(work) is always converted into heat by friction
• The percentage of work transferred by the machine is its efficiency
• Higher efficiency means less friction
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