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# Mechanical Technology - PowerPoint PPT Presentation

Mechanical Technology. Mechanical Advantage Build Challenge: Crane or Rescue Vehicle. Key Ideas. Mechanical Advantage IMA AMA Efficiency Equilibrium Moment/Torque Machine Principle Machine Simple Machine Complex/Compound Machine Work Power. Mechanical Advantage.

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## PowerPoint Slideshow about 'Mechanical Technology' - mimis

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### Mechanical Technology

Crane or Rescue Vehicle

• IMA

• AMA

• Efficiency

• Equilibrium

• Moment/Torque

• Machine

• Principle Machine

• Simple Machine

• Complex/Compound Machine

• Work

• Power

• An expression of the ratio of force output to force input

• Assumes a “perfect world”

• No friction or Thermodynamics

• Distance Travelled by Effort / Distance Travelled by Load

• Considers friction and Thermodynamics

• Force applied by Load / Force applied by Effort

• Efficiency

• A measure of the useable portion of energy in a system

• AMA / IMA

• Assumes a “perfect world”

• Efficiency = 1

• AMA = IMA

• DEFE = DLFL

• FE:FL = DL:DE

• Ratio of Forces is INVERSE of Ratio between Distances

• Beam (LEVER ARM) supported by pivot point (FULCRUM)

• 3 classifications

• One of two PRINCIPLE MACHINES

• Force Multiplier or Distance Multiplier

• “Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.” Archimedes

• Fulcrum between Load and Effort

• EFL

• Load between Fulcrum and Effort

• FLE

• Effort between Fulcrum and Load

• FEL

Wait a “moment!”

• Moment: a measure of the force inducing the tendency of an object to rotate within a system.

• measured by the application of a force some distance from the “center of rotation”

• This is virtually the same concept as “Torque”

• This is NOT the same thing as “Torsion,” the structural stress resulting from moment/torque

• Torque = Moment = F * D = τ

• (that’s a lower-case Greek letter, “tau.”)

• Measured (USCMS) in Foot-Pounds (ftlbs)

• D = Distance travelled by Force

• Assume rotation doesn’t stop

• D = pi*2*radius (distance from fulcrum to force)

• => dEFE = dLFL

• Distance between Effort and Fulcrum * Force of Effort

• Compare these equations to “Moment”

• => dE:dL = hE:hL

• Height travelled = d sin ß

• ß is the same for both sides of the lever, so…

• dE sin ß = dL sin ß

• Therefore dE = dL<<implies>>hE = hL

• Levers can be FORCE MULTIPLERS or DISTANCE MULTIPLERS

• IMA of a Lever: dE / dL

• >1 - Force Multiplier

• =1 - neutral system

• <1 - Distance Multiplier

• Behaves as Class 2 Lever

• ONLY WHEN EFFORT IS APPLIED TO WHEEL!!!!!!!!!

• Behaves as Class 3 Lever

• WHEN EFFORT IS APPLIED TO AXLE!!!!!!!!!

• Force Multiplier, distance reducer

• (steering wheel)

• Distance Multiplier, force reducer

• (automotive transmission)

• D = Distance travelled by Force

• D = pi*2*radius (distance from CoR to force)

• D = pi*diam. = pi*2*rad. = Circum

• => dEFE = dLFL

• Distance between Effort and CoR * Force of Effort

• Compare these equations to “Moment”

• Grooved wheels attached to an axle

• Grooves runs concentrically around the outer rim of the wheel

• Behave like Class 2 Levers

• Direction Changer, Force Multiplier, or Distance Multiplier

• “Open” system or “Closed” system

• DE measured by length of rope

• DL measured by lift of load

• Open pulley systems leave disconnected the ends of the rope/cable/chain/belt

IMA of Fixed Pulley: 1

IMA of fixed pulley: 1

IMA of moving pulley: 2

IMA = 4?!!?

AH!! 2 Pulleys!

• When two or more simple machines are used in conjunction with one another

• Can be same machine (pulleys and pulleys)

• Can be different machines (lever, w/a, pulley)

• Total IMA = Product of simple IMA

• MAT = MA1 * MA2 * … * MAn

• Closed pulley systems have connected the ends of the belt/cable/chain/cable

• Behave somewhat like a wheel-and-axle… just in two pieces

Follower

Resistance

Output

Driver

Effort

Input

Effort

• SEVERAL equivalent equations!!

• New Variables!!

• d = diameter

• τ = torque

• ω = Rotational Velocity (rotations-per-minute; revolutions-per-minute; RPM)

• IMA = dout/din = ωin/ωout

• AMA = τout/τin

Effort

• Second PRINCIPLE MACHINE

• Reduces the force required to lift an object

• Ideal Mechanical Advantage: length of slope / height of slope

• NOT THE SAME AS CALCULATION OF SLOPE ANGLE

• NOT A MOVING OBJECT!

Length of Slope

Height

• Basically two inclined planes connected

• Functions as moving IP

Length of Slope

Length of Slope

½ Face

Face

• EQUATION FOR Wedge EQUILIBRIUM

• 2sE = fL

• 2 * Length of Slope * Force of Effort

• Width of Wedge Face * Force of Load

• EQUATION FOR PULLEY MECHANICAL ADVANTAGE

• 2s / f

• 2 * Length of Slope / Width of Wedge Face

• Theoretical Mechanical Advantage: pi*dm / l

• pi = (appx.) 3.1415 or 22/7

• dm = average diameter of the screw

• l = “lead” of the screw

• axial advance of a helix for one complete turn on a gear

• In other words… the distance between threads

• Same basic idea as Pulleys

• Gears have teeth or spurs extending radially outward from the outer or inner edge of the wheel

• Gears do not slip, as pulleys can

• Gears ALWAYS reverse the direction of rotation between adjacent gears

• Use an “idler gear” between driver and follower to have follower turn in same direction as driver

• Force Multiplier or Speed Multiplier

• SEVERAL equivalent equations!!

• New Variables!!

• d = diameter

• τ = torque

• ω = Rotational Velocity (rotations-per-minute; RPM)

• n = number of teeth

• IMA = nout/nin = dout/din = τout/τin = ωin/ωout

• IMA = “GEAR RATIO”

• WORK = FORCE x DISTANCE

• In a way, measures the conversion of “POTENTIAL ENERGY” into “KINETIC ENERGY”

• No distance = no work.

• No force = no work.

• TORQUE = rotational work

• TORQUE = FORCE x RADIUS

• Power = Work / Time

• Horsepower (hp) = (Force in pounds x Distance in feet) / (Time in seconds x 550)

• Yep… the number (constant) 550…

• HP was originally used by James Watt to describe the “power” equivalence of steam engines in terms we could understand

• This number was chosen… for some reason… but it’s actually twice the number that it should be… the first motor was THAT powerful…

• Electrical Power is measured in WATTS

• 1 Watt = 1 Joule / 1 Second