Download Key Words: inclined plane, simple machine, screw

Unit – “Simple Machines”
Sections – “Inclined Planes,” “Screws,” and “Wedges”
Key Words: inclined plane, simple machine, screw, complex machine, wedge,
Essential Questions:
Inclined Planes
What is an inclined plane?
How does an inclined plane make it easier to lift objects?
How can an inclined plane be used in a system?
Screws
What is a screw?
How does a screw make work easier?
How can a screw be used in a system?
Wedges
What is a wedge?
How does a wedge make work easier?
What is a complex machine?
How can a wedge be used in a system such as a complex machine?
Machine – a device used to make work easier by adjusting the amount or
direction of force applied to the object
- purpose is to reduce the amount of work you have to put in
- law of conservation of energy:
o energy cannot be created nor destroyed, only change form/transferred
 machine cannot
increase the amount of energy used to do work
do more work than you put in
 machine can
change the amount of force or the distance over which force is
applied
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Simple machines – a machine with only 1 movement
o Inclined plane
 a simple machine used for over four thousand years to decrease the effort
required to move heavy objects
 sloped surface (ramp)
 can move a heavy load using less force over a greater distance
 ex. 150 kg fridge (1500N) 1m off the ground
W = (1500N)(1m) = 1500 J
5 m long ramp
o Makes distance 5 times longer than straight up
o Effort force = 1500/5 = 300N
o MA = 5
-
o Screw
 Inclined plane wrapped around a shaft
 Spread over a greater distance
 Fasten materials together
inclined plane creates a groove in the material where it can fit and
hold
 other ways people use screws in machines
opening and closing vices/clamps, drilling, etc.
o Wedge
 uses two inclined planes together to cut or push apart different materials
 Used to cut
 1 or 2 sloping sides
 Ex. Knife, axes, hatchets, chisels, teeth
 amount of force needed to raise an object or split them apart depends on
the angle between the wedge surfaces
Compound machine – combo of simple machines
Section: “Levers”
Key Words: first-class lever, fulcrum, lever, second-class lever, simple machine, third-class lever
Essential Questions:
What is a lever?
How does a lever make work easier?
How can a lever be used in a system?
o Lever

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

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a rod or plank that pivots about a point (fulcrum)
ex. Shovel, teeter-totter, etc.
can help to lift heavy things
Four parts:
lever stick
fulcrum
load
force
position of the fulcrum can make lifting easier or harder
three types of levers:
first-class
o E
F
L
o the fulcrum is positioned between the effort and the load
o the effort is smaller than the load
o the effort moves further than the load
-
o the lever can be considered as a force magnifier
o ex. crowbar, seesaw, scissors, elbow extension
second-class
o E
L
F
o the effort and the load are positioned on the same side of the
fulcrum but applied in opposite directions
o the load lies between the effort and the fulcrum
o the effort is smaller than the load
o the effort moves further than the load
o the lever can be considered as a force magnifier
o ex. wheel-barrow, nutcracker, rowing, standing on toes, pushups
third-class
o L
E
F
o the effort lies between the load and the fulcrum
o the effort is greater than the load
o the load moves further than the effort
o the lever can be considered as a distance magnifier
o ex. tongs, shoveling, kayak paddling, batting, knee and elbow
flexion
(http://www.engineeringtoolbox.com/levers-d_1304.html)
(http://www.exrx.net/Kinesiology/Levers.html)
Section: “Pulleys”
Key Words: Block-and-tackle, compound pulley, fixed pulley, mechanical advantage, moveable pulley, pulley,
simple machine
Essential Questions:
What is a pulley?
How do different types of pulleys make work easier?
How can pulleys be used together in a system to increase mechanical advantage?
o Pulley



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a surface, such as a wheel, that redirects force using rope
load is attached to one end and input effort force the other
MA increases with increased number of pulleys used
can be fixed or move within system (moveable)
fixed
o changes the direction of the input force, not the strength
(magnitude)
o output forces = input force
moveable
o increases the output force, not the direction
2 or more form a “compound pulley”
can change both direction and strength (magnitude)
“block-and-tackle”
MA = output/input
Additional pulleys to system will increase MA
Ropes attached to each pulley help support load and reduce total
input force applied
Section: “Wheels and Axles”
Key Words: simple machine, wheel and axle, mechanical advantage, work
Essential Questions:
What is a wheel and axle?
How does a wheel and axle make it easier to do work?
How can a wheel and axle be used in a system?
o Wheel & axle
 A simple machine made of a larger wheel connected to a smaller wheel or
rod (axle)
 First-class lever that rotates around the fulcrum
circular lever
center is fulcrum
 When you apply an input force to turn the wheel, the output force on the
axle is increased
 But you have to apply the input force to the wheel over a longer distance, so
the amount of work stays the same
 Used in compound machines
Increases the output force on object being turned or moved
Examples
o Doorknob
 Wheel and axles attached to latch
 Handle – wheel
 Increases force on the axle so you can apply less force
on the knob to pull the latch
o Steering wheel
 Increases force to turn the wheels of vehicle
o Cars & bicycles
 Used to increase the distance over which the output
force acts
 Applies the input force to the axle
 Input force is applied to axle
 Output force is reduced but applied over a greater
distance to move forward more easily
Mechanical Advantage
- work produced by a machine can never be greater than the work put into it
- effort force
-
Efficiency
-
o the force you exert
resistance force
o the force you must overcome
work in = work out
if you increase the effort distance, the effort force is decreased
mechanical adv. Compares effort force applied to a machine to the resistance force it must
overcome
o MA – Fr /Fe
o Tells how many times the effort force is increased
the ability of a machine to convert the work input, into the work output
a percentage
efficiency = W out/W in * 100
100% efficiency is ideal – unrealistic
Friction always affects efficiency