Mechanical engineering focuses on designing, producing, and improving technical objects with moving parts. The chapter discusses various mechanical functions including linking parts, guiding motion, transmitting motion, and transforming motion. Motion transmission systems relay motion without changing its nature, while transformation systems alter the motion's nature. Examples of transmission systems are gear trains, chains, belts, and friction gears, while transformation systems include rack and pinion gears, screws, cams, sliders, and eccentrics. Speed and torque considerations are also discussed.

1. MechanicalMechanical
EngineeringEngineering
Chapter 13Chapter 13
ObservatoryObservatory
pp. 424-454pp. 424-454
STST ESTEST
ASTAST SESE

2. What is Mechanical Engineering?What is Mechanical Engineering?
 Mechanical Engineering is the branch ofMechanical Engineering is the branch of
engineering that focuses on the design,engineering that focuses on the design,
production, analysis, working andproduction, analysis, working and
improvement of technical objects withimprovement of technical objects with
moving parts.moving parts.
 Main TopicsMain Topics
• LinksLinks
• GuidingGuiding
• TransmissionTransmission
• TransformationTransformation

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3. Linking in Technical ObjectsLinking in Technical Objects
 Linking is the mechanical functionLinking is the mechanical function
performed by any component thatperformed by any component that
connects different parts of aconnects different parts of a
technical object.technical object.

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4. Degrees of Freedom of MovementDegrees of Freedom of Movement
 The Degrees of Freedom are the setThe Degrees of Freedom are the set
of independent movements that areof independent movements that are
possible for a given part in apossible for a given part in a
technical object.technical object.
 E.g. A door can only rotate aroundE.g. A door can only rotate around
the hinges – 1 degree freedomthe hinges – 1 degree freedom
 E.g. A manual transmission gear shiftE.g. A manual transmission gear shift
moves forward/back and left/right –moves forward/back and left/right –
2 degrees of freedom2 degrees of freedom

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5. Guiding ControlsGuiding Controls
 Guiding is the mechanical functionGuiding is the mechanical function
performed by any component thatperformed by any component that
controls the motion of moving parts.controls the motion of moving parts.
 A Guiding Component or Control is aA Guiding Component or Control is a
component whose mechanicalcomponent whose mechanical
function is to guide the motion offunction is to guide the motion of
moving parts.moving parts.

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6. Types of GuidingTypes of Guiding
 Translational Guiding ensures the straightTranslational Guiding ensures the straight
translational motion of a moving part.translational motion of a moving part.
E.g. a vertical window grooveE.g. a vertical window groove
 Rotational Guiding ensures the rotationalRotational Guiding ensures the rotational
motion of a moving part.motion of a moving part.
E.g. a bicycle wheel hubE.g. a bicycle wheel hub
 Helical Guiding ensures the translationHelical Guiding ensures the translation
motion of a moving part while it rotatesmotion of a moving part while it rotates
about the same axis. E.g. threaded shankabout the same axis. E.g. threaded shank
in a vicein a vice

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7. Adhesion and Friction of PartsAdhesion and Friction of Parts
 Adhesion is the phenomenon by which twoAdhesion is the phenomenon by which two
surfaces tend to remain in contact withsurfaces tend to remain in contact with
each other without slipping.each other without slipping.
 In mechanics, Friction is a force thatIn mechanics, Friction is a force that
resists the slipping of one part overresists the slipping of one part over
another.another.
 Lubrication is the mechanical functionLubrication is the mechanical function
performed by any component that reducesperformed by any component that reduces
friction between two parts.friction between two parts.

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8. Adhesion FactorsAdhesion Factors
 Adhesion is affected by the following factors:Adhesion is affected by the following factors:
• Nature of materials – rubber/ice vsNature of materials – rubber/ice vs
rubber/asphaltrubber/asphalt
• Presence of lubricant – decreases adhesionPresence of lubricant – decreases adhesion
• TemperatureTemperature – cold decreases adhesion– cold decreases adhesion
• State of the surfaces in contact – rough vsState of the surfaces in contact – rough vs
smoothsmooth
• Perpendicular force (weight) on surface –Perpendicular force (weight) on surface –
more weightmore weight  more adhesionmore adhesion

9. Motion Transmission SystemsMotion Transmission Systems
 Motion Transmission is theMotion Transmission is the
mechanical function of relaying amechanical function of relaying a
motion from one part to anothermotion from one part to another
without altering the nature of thewithout altering the nature of the
motion.motion.
 A Motion Transmission System is aA Motion Transmission System is a
set of components that perform theset of components that perform the
function of transmitting motion.function of transmitting motion.

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10. Characteristics of Motion inCharacteristics of Motion in
Transmission SystemsTransmission Systems
 The most common rotationalThe most common rotational
transmission systems are:transmission systems are:
 Gear TrainsGear Trains
 Chain and Sprocket SystemsChain and Sprocket Systems
 Worm and Worm Gear SystemsWorm and Worm Gear Systems
 Friction Gear SystemsFriction Gear Systems
 Belt and Pulley SystemsBelt and Pulley Systems

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11. Types of Components in aTypes of Components in a
Mechanical SystemMechanical System
 Driver component: receives the forceDriver component: receives the force
required to activate the system –pusherrequired to activate the system –pusher
 Driven component: receives the motionDriven component: receives the motion
and transfers it to another part - pusheeand transfers it to another part - pushee
 Intermediate component: locatedIntermediate component: located
between the driver and driven componentbetween the driver and driven component
– not all systems have this.– not all systems have this.
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12. Construction Considerations forConstruction Considerations for
Motion TRANSMISSION SystemsMotion TRANSMISSION Systems
 Depending on the need, a systemDepending on the need, a system
may only rotate in one direction.may only rotate in one direction.
 That will affect the choice of system.That will affect the choice of system.

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13. Gear TrainsGear Trains
 The direction of rotation changesThe direction of rotation changes
from one wheel to the next.from one wheel to the next.
 The system can be reversed.The system can be reversed.

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14. Gear Train FactorsGear Train Factors
 Gear teeth: all the gear teeth in a systemGear teeth: all the gear teeth in a system
must be identical – same shape, direction,must be identical – same shape, direction,
size and be equally spaced. E.g. Straightsize and be equally spaced. E.g. Straight
or helicalor helical
 Gear type: the rotational axis of the gearsGear type: the rotational axis of the gears
can be positioned different ways.can be positioned different ways.
 Gear size: the greater the number ofGear size: the greater the number of
teeth, the fewer the speed of rotation – orteeth, the fewer the speed of rotation – or
bigger diameterbigger diameter  slower speed.slower speed.
 a/k/a big & slow, small & fasta/k/a big & slow, small & fast

15. Chain and Sprocket SystemsChain and Sprocket Systems
 The direction of all sprockets on theThe direction of all sprockets on the
same side of the chain is the same.same side of the chain is the same.
 A sprocket on the other side of theA sprocket on the other side of the
chain moves in the oppositechain moves in the opposite
direction.direction.
 It can be reversed.It can be reversed.

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16. Worm and Worm Gear SystemsWorm and Worm Gear Systems
 The direction of rotation depends onThe direction of rotation depends on
the direction of the threads on thethe direction of the threads on the
worm screw shaft.worm screw shaft.
 It is not reversible.It is not reversible.

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17. Friction Gear SystemsFriction Gear Systems
 Friction gear systems are similar toFriction gear systems are similar to
gear trains except that motion isgear trains except that motion is
transferred by FRICTION and not bytransferred by FRICTION and not by
the GEAR TEETH.the GEAR TEETH.
 They are less efficient because ofThey are less efficient because of
slippage.slippage.
 Factors that affect friction gearFactors that affect friction gear
systems are: gear type (straight,systems are: gear type (straight,
bevel or spherical), gear size andbevel or spherical), gear size and
choice of material.choice of material.

18. Friction Gear SystemsFriction Gear Systems
 The directionThe direction
alternates fromalternates from
one gear to theone gear to the
next.next.
 It is reversible.It is reversible.

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19. Belt and Pulley SystemsBelt and Pulley Systems
 Similar to the chain and sprocket system.Similar to the chain and sprocket system.
 The chain is replaced by a belt.The chain is replaced by a belt.
 The sprocket is replaced by a pulley.The sprocket is replaced by a pulley.
 The choice of the belt material and theThe choice of the belt material and the
tightness of the belt affect the friction andtightness of the belt affect the friction and
hence the efficiency of the system.hence the efficiency of the system.
 The direction is the same for any pulley onThe direction is the same for any pulley on
the same side of the belt.the same side of the belt.
 It is reversible.It is reversible.

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20. Speed Changes in Motion TransmissioSpeed Changes in Motion Transmissio
 A Speed Change occurs in a motionA Speed Change occurs in a motion
transmission system when the drivertransmission system when the driver
does not turn at the same speed asdoes not turn at the same speed as
the driven component(s).the driven component(s).

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21. Speed Changes in GearSpeed Changes in Gear
Train/Friction Gear SystemsTrain/Friction Gear Systems
 The Speed or Gear Ratio depends on the #
gear/threads/diameter of the driver/driven gear.
 Gear/Speed Ratio = Driver Gear
Driven Gear
Calculate speed of driven gear if the driver gear
has 100 teeth and turns at 50 rpm and the driven
gear has 20 teeth. Gear Ratio = 100 teeth = 5
20 teeth
Therefore the smaller (faster) gear’s speed is
50 rpm x 5 = 250 rpm
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22. Speed Changes in Worm andSpeed Changes in Worm and
Worm GearWorm Gear SystemsSystems
 Relative to the worm, the more teethRelative to the worm, the more teeth
a worm gear has, the slower itsa worm gear has, the slower its
speed.speed.
 To increase the speed of the wormTo increase the speed of the worm
gear, it should have less teeth.gear, it should have less teeth.

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23. Speed Changes in a PulleySpeed Changes in a Pulley
Transmission SystemTransmission System
 To increase the speed, the drivenTo increase the speed, the driven
component should have a smaller diameter.component should have a smaller diameter.
 To decrease the speed, the drivenTo decrease the speed, the driven
component should have a larger diameter.component should have a larger diameter.
 Gear Ratio =Gear Ratio = Driver DiameterDriver Diameter == 5 cm5 cm == 11
Driven Diameter 15 cm 3Driven Diameter 15 cm 3
 The driven pulley is 3 times SLOWERThe driven pulley is 3 times SLOWER
 E.g. If the driver turns at 30 rpm, then theE.g. If the driver turns at 30 rpm, then the
driven turns at 30 /3 = 10 rpm.driven turns at 30 /3 = 10 rpm.
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24. TorqueTorque
 Torque involves two forces of equalTorque involves two forces of equal
strength but applied in opposite directionsstrength but applied in opposite directions
which cause a component to rotate aboutwhich cause a component to rotate about
an axis.an axis.
 E.g.E.g. Arm wrestlingArm wrestling , if done, if done correctlycorrectly..
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25. Torque and Speed ChangeTorque and Speed Change
 Engine Torque increases theEngine Torque increases the
rotational speed of components inrotational speed of components in
mechanical systems.mechanical systems.
 Resisting Torque slows or stops theResisting Torque slows or stops the
rotation of components in mechanicalrotation of components in mechanical
systems.systems.
 If the ratio of the torque strengthIf the ratio of the torque strength
between the driver and the driven is:between the driver and the driven is:
• =1=1  No speed changeNo speed change
• >1>1  Increased speedIncreased speed
• <1<1  Decreased speedDecreased speed
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26. TRANSFORMATION SystemsTRANSFORMATION Systems
 Motion transformation is theMotion transformation is the
mechanical function of relaying amechanical function of relaying a
motion from one part to anothermotion from one part to another
while altering the nature of thewhile altering the nature of the
motion.motion.
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27. Characteristics of Motion inCharacteristics of Motion in
TRANSFORMATION SystemsTRANSFORMATION Systems
The most common systems are:The most common systems are:
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Type Driver Motion Driven Motion Reversible
Rack & Pinion Rotation
Translation
Translation
Rotation
Yes
Screw Gear,
Type 1
Rotation Translation No
Screw Gear,
Type 2
Rotation Translation No
Cam & Follower Rotation Translation No
Slider Crank Rotation
Translation
Translation
Rotation
Yes

28. Rack and Pinion SystemsRack and Pinion Systems
 The rack is the straight bar withThe rack is the straight bar with
teeth.teeth.
 The pinion is the gear part.The pinion is the gear part.
 It is used in many steering systems.It is used in many steering systems.
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29. Screw Gear SystemsScrew Gear Systems
 The screw gear uses a threaded boltThe screw gear uses a threaded bolt
to move another gear or itself.to move another gear or itself.
 Type 1 Type 2____Type 1 Type 2____
Car Jack Pipe WrenchCar Jack Pipe Wrench


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30. Cam and Follower SystemsCam and Follower Systems
 A cam is an non-circular wheelA cam is an non-circular wheel
and acts as the driver.and acts as the driver.
 The follower is the driven gear.The follower is the driven gear.
 This is used in car timingThis is used in car timing
mechanisms for the intake of gasmechanisms for the intake of gas
into the piston chamber.into the piston chamber.
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31. EccentricsEccentrics
 An eccentric is a cam whose centreAn eccentric is a cam whose centre
of rotation is off-centre.of rotation is off-centre.

32. Slider-crank MechanismsSlider-crank Mechanisms
 The slider is the piston.The slider is the piston.
 The crank attaches the piston toThe crank attaches the piston to
another wheel.another wheel.
 In cars, the piston is the slider is theIn cars, the piston is the slider is the
driver.driver.
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33. Check Up!Check Up!
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 Chapter 13 – Page 451-2Chapter 13 – Page 451-2
 Q. 7-11Q. 7-11
 Q. 12 - 17Q. 12 - 17