9 mechanical power systems permission granted to reproduce for educational use only.©...
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9Mechanical Power Systems
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Basic Concepts• List the six simple machines and give an
example of each.• List three types of gears. • Name the two primary characteristics of
power.• Identify two mechanical transmission
devices and describe how each operates.• Define mechanical advantage and give an
example.• Recognize the difference between the ideal
mechanical advantage (IMA) and actual mechanical advantage (AMA).
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Intermediate Concepts• Discuss force and rate in a mechanical
system.• Describe the difference between scalar and
vector quantities.
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Advanced Concepts• Design a mechanical system for a specific
application.• Predict the result of a mechanical system
based on knowledge of balanced and unbalanced loads.
• Calculate the mechanical advantage of a simple machine.
• Compute the mechanical advantage of compound machines.
• Solve for the percentage of frictional loss in a mechanical system.
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Mechanical Systems
• Produce work using one or more machines• Machines can change size, direction, and
speed of forces• Machines can change type of motion
produced
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Simple Machines
• Levers• Pulleys• Wheels and axles• Inclined planes• Screws• Wedges
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Simple Machines
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Levers
• Rotates around fulcrum• Position of fulcrum, load, and input force
determines lever class– First-class levers– Second-class levers– Third-class levers
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Pulleys
• Discs rotating around center axis• Operate on principle of levers• Several pulleys together make block and
tackle
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Wheels and Axles
• Also based on principle of levers• Large-diameter wheel and small-diameter
axle are attached to each other• Can be used to change size or distance of
force
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Inclined Planes
• Makes use of sloping surfaces
• Rolling objects up slopes is easier than lifting objects
• Much less force to achieve same result
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Screws
• Operates on principle of inclined planes• Long incline plane wrapped around shaft• Screws with more threads per inch have
advantages– Apply greater force– Create for surface area to produce friction
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Wedges
• Consist of two inclined planes placed back to back
• Often used to split materials
• Hatchets are wedges that use weight and fast movement to split wood
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Gears
• Metal wheel with small notches cut into rim• Gear sets are made so gear teeth interlock
and drive each other• Gears can control mechanical power in the
same way as belts and pulleys• Gears change direction of power, speed, and
torque
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Quantities of Measurement
• Scalar quantity represents physical quantity and is expressed by number or unit
• Vector quantities have both magnitude and direction– Displacement– Velocity
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Torque
• Force that produces twisting or turning effect or rotation
• Two components– Amount of force
applied to lever arm
– Radius of lever arm itself
• Measured using Prony brake
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Horsepower (hp)
• Rate at which output work is performed• Several types of hp ratings:
– Indicated horsepower (ihp)– Brake horsepower (bhp)– Frictional horsepower (fhp)
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Net Forces of Balanced and Unbalanced Loads• Balanced forces are in state of equilibrium• Movement ceases in balance• Forces of effort and opposition must be
totally balanced• Unbalanced loads can be calculated with
addition and subtraction
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Transmission of Mechanical Energy• Compound machines use two or more
simple machines• Variations in simple machines may be used• Operations of industrial machines and
transportation vehicles rely on principles of one or more simple machines
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Clutches
• Connects power source to rest of machine• Device is needed so vehicles can remain at
rest with engine running, start without stalling, and shift gears while moving
• Operate on principle of friction• Types in vehicles are diaphragm clutch and
centrifugal clutch
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Pulleys and Belts
• Many belts move around pulleys in vehicles• Transmit power from engine to drive engine
components, such as water pump and fan• Control mechanical energy through five
different arrangements
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Chains and Sprockets
• Found on bicycles, mopeds, and motorcycles• Usually used as drive system to bring power
to driving wheel of vehicle• Provide positive power transfer, which
means chain cannot slip like belt on pulley
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Shafts and Bearings
• Shafts are vital parts of automobile engines and drive systems
• Bearings are made to be strong and allow shaft to turn inside them
• Shafts are not easily bent, so universal joints are used when flexibility is needed
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Mechanical Advantage
• Simple machines can gain mechanical advantage– Levers– Pulleys– Wheels and axles– Inclined planes– Wedges– Gears
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Ideal Mechanical Advantage vs. Actual Mechanical Advantage• Ideal mechanical advantage (IMA)• Actual mechanical advantage (AMA)
– Accounts for loss of energy through friction– Friction is heat energy that is common by-
product of mechanical energy– AMA is always less than IMA because IMA
assumes for 100% efficiency– AMA accounts for frictional losses
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ReviewWhat are the six simple machines?Levers, pulleys, wheels and axles, inclined
planes, screws, and wedges
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ReviewWhat two simple machines also operate on
the principle of the lever?Pulleys and wheels and axles
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ReviewWhat type of quantity is displacement?Vector quantities