ME2203 Kinematics of Machinery R-2008 Lecturer Notes

Department of Mechanical Engineering
Question Bank
Subject Code / Subject : ME2203 / Kinematics of Machinery Year / Sem : II / III
Part A
UNIT – 1 BASICS OF MECHANISMS
1. Differentiate between Machine and Mechanism.
Machine: Machine is a mechanism or collection of mechanism which transmits force from the source of power to the resistance (load) to overcome and thus performs useful mechanical work.
Combination of rigid or resistant bodies connected that they move upon each other with definite relative motion E.g Lathe, Shaping Machine etc. E.g single slider mechanism in IC engine
All machines are mechanism All mechanisms are not Machine

2. Write down Kutzbach criterion to find the mobility of a planar mechanism.
The Kutzbach criteria which calculates the mobility.
F = 3(n – 1) – 2j
Where, F- Degrees of freedom
n – number of links
J – number of joints

3. Define transmission angle.
The acute angle between the coupler and the driven link.

4. Enumerate the difference between a Machine and a Structure.
Machine Structure
Machine is a mechanism or collection of mechanism which transmits force from the source of power to the resistance (load) to overcome and thus performs useful mechanical work.

Structure is the assemblage of resistant bodies without any relative motion between the linksE.g IC engine E.g Bridges
All machines are mechanism
5. List out the inversions of a double slider crank chain.
Inversions of Double Slider Mechanism
First Inversion – Scotch Yoke mechanism
Second Inversion – Oldhams Coupling
Third Inversion – Elliptical trammel
Fourth Inversion – Hand Pump
6. Define Degree of Freedom and give the DOF for a shaft in a circular hole.
The number of independent input parameters which must be controlled independently so
that a mechanism fulfills its useful engineering purpose.
7. State Grashof’s law for a four bar linkage.
It states that for a planar four bar linkage, sum of the shortest and longest link – lengths
must be less than or equal to the sum of the remaining two link-lengths, is there is to be a
continuous relative motion between two members
S + L ≤ P + Q
Where, S – Length of shortest link
L – length of longest link
P and Q – remaining two link lengths
i) If L + S < P + Q, then we call this a Grashof Mechanism
G.1 = crank-rocker if S is the crank and either of the
adjacent link is the fixed link
G.2 = double-crank if S is the fixed link
G.3 = double-rocker if the link opposite S is the fixed link
ii) If L + S > P + Q, then we call it non-Grashof mechanism
only double-rocker: no link is capable of making a complete revolution
iii) If L + S = P + Q, it can have G.1~G.3 and
parallelogram form (colinear)
8. Define degree of freedom.
It is defined as the minimum number of input parameters which must be independently
Controlled, inorder to bring the mechanism into a useful engineering purpose.
9. Define kinematic pair and illustrate any two types of constrained pair
When two kinematic links are connected in such a way that their motion is either
completely or successfully constrained, these two links are said to form a kinematic pair.
E.g foot step bearing, circular shaft in the circular slot
10. Define Pantograph
A pantograph is a mechanism used to produce paths on an enlarged or reduced scale as
exactly as possible the path described by a given point. It is based on four bar kinematic
chain
11. Define Link and List the various type of link
Link is a resistant body is one which is capable of transmitting the required motion and
force with negligible deformation in the direction of force transmission.
Types of links : 1)Rigid Link 2) Flexible link 3) Fluid link
12. Define the kinematic chain
Kinematic chain is defined as the combination of kinematic pairs in which each link
forms a pair of two kinematic pairs and the relative motion between the links is either
completely constrained or successfully constrained.
When a number of links connected in space make relative motion of any point on a link
with respect to any other point on the other link follow a definite law it is known as
kinematic chain.
13. Name the inversions of four bar mechanisms
Inversions of four bar mechanisms
First Inversion – Coupled wheels of locomotive – double crank
Second Inversion – Beam Engine - Crank and lever mechanism
Third Inversion – Watt’s Engine Indicator – Double lever mechanism
14. Name the inversions of single slider mechanism
Inversions of Single Slider Mechanism
 First Inversion – Reciprocating engine mechanism
 Second Inversion – Gnome Engine or Rotary Engine – Whitworth quick return
mechanism
 Third Inversion – Quick return mechanism – Crank and slotted lever – Oscillating
cylinder engine
 Fourth Inversion – Hand Pump
15. Name some straight line generating mechanism
 Peaucellier mechanism
 Scott Russel mechanism
 Hart’s mechanism
16. Write down the Grubler’s criteria for planar mechanism
The following equation is used to describe mobility in 2D or planar systems:
M = 3(N-1) – 2 f1 – f2
Where,n = total number of links
M = DOF
f1 = number of 1DOF joints
f 2 = number of 2 DOF joints
This is known as GRUBLER’S EQUATION and is for mobility of planar systems.
M = 0  Motion impossible - statically determinate
M = 1  Single input /monitoring necessary
M = 2  Double input/output necessary
M = -1  Statically indeterminate structure
17. Define Kinematic Pair
When two links are in contact with each other it is known as a pair.If the pair makes
constrain motion it is known as kinematic pair.
18. Classify the kinematic pair based on the various characteristics
Kinematic pairs are classified on the basis of the following characteristics
1) Type of relative motion between contacting elements
2) Type of contact between contacting elements
3) Number of degrees of freedom
4) Type of closure
19. Define Higher and lower pair
Kinematic pairs in which there is a surface (area) contact between the contacting
elements. All revolute pairs, sliding pairs, screw pairs, globular pairs, cylindrical pairs
and flat pairs fall in this category.
Kinematic pairs in which there is a point or line contact between the contacting elements
are called as higher pair. Meshing gear teeth, cam and follower pair, wheel rolling on a
surface, a ball and roller bearings and pawl and ratchet are of higher pair.
When the two element of a pair have a line or point contact when the relative motion
takes place and the motion between the two elements is partly turning and partly sliding,
then the pair is known as higher pair
20. Define kinematic inversion
A mechanism is formed by fixing one of the links of a chain. The process of choosing
different links of a kinematic chain for becoming frame.
21. Define Mechanical Advantage
It is defined as the ratio of the output torque, supplied by the driven link, to the input
torque, required to be supplied to the driver link.
22. What is meant by planar mechanism
A planar mechanism is one in which all particles describe plane curves in space and all
these curves lie in parallel planes: that is, the loci of all points are plane curves parallel to
a single common plane. It utilizing only lower pairs is called planar linkages, they include
only prismatic and revolute pairs.
23. What is meant by spatial mechanism
If there is any relative motion that is not in the same plane or in parallel planes, the
mechanism is called spatial mechanism. Spatial mechanisms are three dimensional.
24. What are the methods for determining the velocity of a point on a link?
Instantaneous centre method,WWW.VIDYARTHIPLUS.COM
WWW.VIDYARTHIPLUS.COM V+ TEAM
Relative velocity method
26. Write down the Kutzback criteria for spatial mechanism.
According to Kutzback criterian,
Mobility, n = 6(N-1)-5PI-4P2-3P3-2P4-1p5
UNIT – II KINEMATIC ANALYSIS
1. How will you determine the magnitude and direction of Coriolis component of
acceleration ?
The direction of the Coriolis component of acceleration can be determined by rotating
the velocity of a sliding vector Vs through 90˚ in the direction of rotation of angular
velocity ω
The magnitude of Coriolis component of acceleration can be determined by
F = 2 Vs ω
=Angular velocity
 Vs =Linear velocity
2. Define rubbing velocity.
The links in a mechanism are mostly connected by means of pin joints. The rubbing
velocity is defined as the algebraic sum between the angular velocities of the two
links which are connected by pin joints, multiplied by the radius of the pin.R = w.r.
3. Define Corioli's component of acceleration.
The corioli’s component of acceleration has two components of acceleration i.e. the
vector sum of tangential acceleration and centripetal acceleration.
4. Define Instantaneous center of rotaion
Instantaneous center of rotation (Kinematics), in a plane or in a plane figure which
has motions both of translation and of rotation in the plane, is the point which for the
instant is at rest.
Instantaneous axis of rotation (Kinematics), in a body which has motions both of
translation and rotation, is a line, which is supposed to be rigidly united with the
body, and which for the instant is at rest. The motion of the body is for the instant
simply that of rotation about the instantaneous axis
5. Illustrate the space centrode and body centrode
The trace of the locus of the center of rotation on the body is the body centrode and in
space is the centrode.
6. State the properties of instantaneous centre method
 An Instantaneous centre of rotation is a point common to two links having
relative motion.
 IC is a point about which one body can be assumed to rotate with respect to
the oother
 It is an imaginary point at which the two bodies have same absolute velocity,
It follows that the two bodies have zero relative velocity at the coincident
points I.
 IC is in general not a stationary point, because the mechanism moves from
one position to another, the velocities of points like A and B keep on
changing.
7. Name the various components of acceleration
Radial component of acceleration
Tangential component of acceleration
8. State and explain the kennedy’s theorem
It states that if three bodies are in relative motion with respect to one another, the
three relative instantaneous centres of velocity are collinear.
9. List the various types of instantaneous centres. What is the formulation to
calculate the no of instantaneous centres are in a mechanism
The various types of instantaneous centres are
1. Fixed
2. Permanent
3. Neither fixed or permanent
Formula to calculate the no of instantaneous centre is
n (n-1) / 2
10. What are the expression for radial and tangential component of acceleration?
Radial component
 a
r
OB=OB*OB
Tangential component
 a
r
OB=OB*OB
 Where, OB=Angular velocity of link OB
 OB=Angular acceleration of link OB
 OB=Length of link OB.
UNIT – III KINEMATICS OF CAMS
1. List the classifications of cam followers based on shape.
Cam followers are classified based on shape as follows
1. Knife edge follower
2. Roller follower
3. Flat followe
4. Spherical follower
2. What are the various types of motions of follower
The cam rotates at a uniform angular velocity, the follower may have the following
motions
1. uniform velocity or uniform motion
2. simple harmonic motion SHM
3. Uniform acceleration and retardation
4. Cycloidal motion
3. What are the classifications of cams based on contact surfaces?
Cylindrical cam and Radial or Disc cam
4. State the basic requirements for high speed cams.
5. What are the necessary elements of a cam mechanism?
Cam-The driving member is known as the cam
Follower-The driven member is known as the follower.
Frame-It supports the cam and guider the follower.
6. What is prime circle of a cam? What is the radial distance between the prime circle
and base circle for a cam with knife edge follower?
Prime circle is the smallest circle drawn to the pitch curve from the centre of rotation of
cam.
7. Define Cam
A cam may be defined as a machine element having a curved outline or a curved groove,
which, by its oscillation or rotation motion, gives a predetermined specified motion to
another element called the follower . The cam has a very important function in the
operation of many classes of machines, especially those of the automatic type, such as
printing presses, shoe machinery, textile machinery, gear-cutting machines, and screw
machines
8. Define pitch curve of the cam.
The path generated by the trace point at the follower is rotated about a stationary cam.
i.e., BY holding the cam fixed and rotating the follower in a direction opposite to that of
cam, then the curve generated by the locus of the trace point is called the pitch curve.
9. Define Radial follower
When the motion of the follower is along an axis passing through the centre of the cam it
is known as radial follower.
10. Define offset follower.
When the motion of the follower is along as axis away from the cam centre it is called
offset follower.
11. Briefly explain the features of mushroom followers
Mushroom followers is used where the space is limited
12. Why roller follower is preferred to knife edge follower
Excessive wear of the knife edge follower is reduced by roller follower
13. Define pressure angle
Pressure angle represents the included angle at any point on the pitch curve between the
line of motion of follower and normal to that point on the cam profile. This angle is of
great importance in designing the cam profiles.
14. Define undercutting in cam. How it occurs? How can you prevent undercutting in cam ?
The cam profile must be continuous curve without any loop. If the curvature of the pitch
curve is too sharp, then the part of the cam shape would be lost and thereafter the
intended cam motion would not be achieved. Such a cam is said to be undercut.
Undercutting occurs in the cam because of attempting to achieve too great a follower lift
with very small cam rotation with a smaller cam.
Prevent undercutting in cam
- By decreasing the follower lift.
- By increasing cam rotation angle.
- By increasing the cam size' (i.e., Base circle).
UNIT – IV GEARS
1. Define (a) Module (b) Diametral Pitch of gears.
Module (m): is the ratio of pitch diameter to the number of teeth on the gear. m = D/T,
where D- pitch circle diameter, T – no of teeth
Diametrical Pitch : It is the number of teeth per unit pitch circle. = T/D
2. What is axial pitch of a helical gear?
It is the distance, parallel to the axis, between similar faces of adjacent teeth. It is same as
circular pitch and is therefore denoted by pc. The axial pitch may also be defined as the
circular pitch in the plane of rotation or the diameteral plane.
3. List out the applications of epicyclic gear train.
Epicyclic gear trains are used in the differential gear box of an automobile, wrist watches,
hoists, pulley blocks, back gear of lathe machine, in aircrafts etc.
4. Define epicycles gear train.
 In a gear train when the axes of shafts over which the gears are mounted move
relative to a fixed axis is called epicyclic gear train.
5. Define velocity ratio.
 Velocity ratio of a simple gear train is defined as the ratio of the angular velocity of
 the first gear in the train to the angular velocity of the last gear.
6. Define gear train.
 A combination of gears that is used for transmitting motion from one shaft to another
 shaft is known as gear train. E.g. spur gear, spiral gear.
.
7. What is the principle reason for employing non standard gears?
a) To eliminate the undercutting.
b) To prevent interference.
c) To maintain reasonable contact ratio
8. What is the principle reason for employing non standard gears?
a) To eliminate the undercutting.
b) To prevent interference.
c) To maintain reasonable contact ratio
9. When in volute interference occurs.
If the teeth are of such proportion that the beginning of contact occurs before the
interference point is met then the involute proportion of the driven gear will mate a
non in volute portion of the driving gear and involute interference is said to occur.
10. Define cycloid.
A cycloid is the curve traced by a point on the circumference of a circle which rolls
without slipping on a fixed straight line.
11. Define gear tooth system.
A tooth system is a standard which specifies the relationship between addendum,
dedendum, working depth, tooth thickness and pressure angle to attain interchangeability
of gears of tooth numbers but of the same pressure angle and pitch
12. What are the conditions to be satisfied for interchangeability of all gears.
For interchangeability of all gears, the set must have the same circular pitch, module,
diameter pitch, pressure, angle, addendum and dedendum and tooth thickness must be
one half of the circular pitch.
13. List out the characteristics of involute action.
 a) Arc of contact.
 b) Length of path of contact.
c) Contact ratio.
14. Define I) path of contact. II) Length of path of contact.
 Path of contact: It is the path traced by the point of contact of two teeth from the
beginning to the end of engagement.
Length of path of contact: It is the length of common normal cut- off by the
addendum circles of the wheel and pinion.
15. Define circular pitch.
 It is the distance measured on the circumference of the pitch circle from a point
of one tooth to the corresponding point on the next tooth. It is denoted by Pc
 Circular pitch Pc= π/DT
 Where D = Diameter of pitch circle.
 T = Number of teeth on the wheel
16. List out the function of differential gear used in the rear drive of an automobile.
 a) To transmit motion from the engine shaft to the rear driving wheels.
 b ) To rotate the rear wheel of different speeds while the automobile is taking a turn.
17. What is reverted gear train?
A reverted gear train is a compound gear train in which, the first and last gears are
coaxial with each other. E.g In clocks and simple lathes where back gear is used to impart
slow speed to the chuck
18. Define undercutting in Gears.
The under cutting concept in gearing is, when the two gears mates, pinions whose base
circle is more than the dedendum circle, therefore the profile of tooth below the base
circle is non– involute. In this case the profile of wheel and pinion will not be tangent to
each other and the tip of the wheel will dig out or interfere with the flank of the pinion
and remove the part of material called under cut and the process of removal of material is
under cutting of gears. The teeth of pinion will become weak due to undercutting.
19. What is meant by Angle of dwell?
It is the angle through which the cam rotates while the follower remains stationary at
the highest or the lowest .
\
20. What are the properties of involute tooth profile
a) A normal drawn to an involute at pitch point is a tangent to the base circle.
b) Pressure angle remains constant during the mesh of an involute gears.
c) The involute tooth form of gears is insensitive to the centre distance and depends only
on the dimensions of the base circle.
d) The radius of curvature of an involute is equal to the length of tangent to the base
circle.
e) Basic rack for involute tooth profile has straight line form.
21. What is meant by contact ratio
It is defined as average number of pairs of teeth which are in contact. It is the ratio of
length of arc of contact to circular pitch.
22. Define pressure angle and explain the effect of different pressure angle.
The pressure angle is the angle which the common normal to the contacting tooth
profiles, at the point of contact, makes with the common tangent to the two pitch circles
at the pitch point.
23. Discuss the advantages of involute gear tooth profile.
a) It is easy to manufacture and the center distance between a pair of involute gears
can be varied without changing the velocity ratio. Thus close tolerances between
shaft locations are not required. The most commonly used conjugate tooth curve is
the involute curve.
b) In involute gears, the pressure angle, remains constant between the point of tooth
engagement and disengagement. It is necessary for smooth running and less wear of
gears.
c) The face and flank of involute teeth are generated by a single curve where as in
cycloidal gears, double curves (i.e. epi-cycloid and hypo-cycloid) are required for
the face and flank respectively. Thus the involute teeth are easy to manufacture than
cycloidal teeth.
24. Describe the advantages and applications of helical, bevel and worm gears
Helical gear :
Applications : These are highly used in transmission because they are quieter even at
higher speed and are durable. The other possible applications of helical gears are in
textile industry, blowers, feeders, rubber and plastic industry, sugar industry, rolling
mills, food industry, elevators, conveyors, cutters, clay working machinery, compressors
and in oil industry.
25. Define gear tooth system.
 A tooth system is a standard which specifies the relationship between addendum,
 dedendum, working depth, tooth thickness and pressure angle to attain
interchangeability of gears of tooth numbers but of the same pressure angle and pitch
26. What is meant by arc of contact
It is the path traced by a point on the pitch circle from the beginning to the end of
engagement of two meshing teeth.
27. State and prove law of gearing
The common normal at the point of contact between a pair of teeth must always pass
through the pitch point for all positions of the mating gears.
28. How the gears are classified?
a) Based on teeth: Straight teeth- Spur, Helical- Helical and Herring Bone,
Inclined Teeth – Bevel Gears, Curved teeth – Spiral Gears
b) Based on engagement: External Gear, Internal Gear, Rack and Pinion
Common type – Spur, Helical, bevel, Worm and worm wheel
29. Define angle of obliquity or Pressure angle
Angle between the common normal of two gear teeth profile at the point of contact and
the common tangent at the pitch point.
30. What is the commonly used Gear Profile?
14 involute profile, Cycloidal involute, 20 full depth involute.
31. What is corrected Gear?
In many cases it is advantages to correct the gear by shifting the profile of the
cutter by a small amount. The gear tooth profile remains as a part of involute curve as in
the case of standard in corrected gearing, but a different portion of involute gear of the
same base circle is used as active profile. These gears are called corrected gears.
32. What are advantages of toothed gears over other type of transmission system?
 a) Positive drives – No slip, no variation in velocity ratio
b) Suitable for short distances
c) High power transmission
d) Change of speed is easy
33. What is meant by interference of Gears?
Gear profile usually starts from base circle and ends with tip circle gear teeth and made
in such a way that their contact is along the profile. Since the top surface of teeth is
made flat the tip of the teeth of one gear tends to dig into the bottom flank of mating
gears. This action is called interference. It can be overcomed by undercutting the tooth
of gears i.e. to remove some of the material in the root of the gear teeth
34. What are the advantage of Helical gears over Spur Gears
a) Noise less operation
b) High power transmission
c) Fully engaged
d) High speed operation
e)
35. What are the two important failure modes in Gears
Tooth Breakage, Pitting of Tooth Surface, Abrasive Wear, Seizing of teeth.
36. Why helical gear tooth is stronger than spur gear?
The teeth of helical gear are inclined to axis of gear. During meshing the helical gears are
made to contact in point whereas spur gears are in line contact. Therefore helical gear
tooth are stronger than spur gear tooth.
UNIT – V FRICTION
1. Distinguish between sliding and rolling friction.
Sliding Friction – When two dry surfaces have a sliding motion relative to each other,
then it is called as sliding friction e.g friction between nut and bolt.
Rolling friction – When two dry surfaces have a rolling motion relative to each other,
then it is called as rolling friction E.g – friction in ball and roller bearings.
2. State the condition for transmission of maximum power in belt drives.
The velocity of the belt v = √ (Tmax / 3m)
3. What is bearing?
A bearing is a machine element which supports another moving machine element known
as journal. It permits a relative motion between the contact surfaces of the member while
carrying the load.
4. What are the factors to be considered when designing a disc or plate clutch?
When there is a uniform pressure
When there is a uniform axial wear.
5. What are the functions of clutch?
To engage or disengage the rest of transmission as required.
To transmit the engine power to rear wheels when the rear wheels without shock.
To enable the gear to get engaged when the vehicle is in motion.
6. What is clutch?
A clutch is a machine member used to connect a driving shaft to a driven shaft so
that the driven shaft may be stared or stopped at with or with out stopping the driving
shaft. It is used in automobile.
7. Where is a V belt used?
The V belt is mostly used in the factories and workshops where a great amount of power
is to be transmitted from one pulley to another when the two pulleys are very near to each
other.
8. What are the factors that have to be considered for the selection of a belt drive?
Speed of the driving and driven shafts.
Speed reduction ratio
Power to be transmitted
Shaft lay out
Space available
9. List out any four desirable characteristics of brake lining material.
a)It should have low wear rate
b) High heat resistant
c) It should have high coefficient of friction with minimum fading
d) It should have adequate mechanical strength and high heat dissipation capacity
e) E.g materials – bronze, steel, wood on cast iron and fiber, asbestos, leather, cork on
metal,
10. What is creep in the case of belt
The relative motion between belt and pulley surface due to unequal stretching of the two
sides of drive. The effect of creep slow down the speed of the belt on the driving pulley
than the peripheral velocity of pulley.
11. Discuss the advantages of V belts
It provides longer life 3 to 5 years
It can be easily installed and removed
High velocity ratio
Drive is positive.
12. What is meant by self locking and over hauling screw
If Φ < α, then the torque required to lower the load will be negative i.e load will start
moving downward without applying any torque. Is known as overhauling of screws.
If Φ > α, the torque required to lower the load will be positive i.e some of torque is
required to lower the load such a screw is know as self locking screw
13. Name the various types of pivot bearing
Based on the shape of the end of shaft and the shape of bearing surface,
1. Flat pivot bearing
2. Flat collar bearing
3. Conical pivot bearing
4. Truncated conical or trapezoidal bearing
5.
14. Define brake and name its various types
The frictional force is used to absorb the energy possessed by a moving member.
Various types of brake
1. Block or shoe brake
2. Band brake
3. Band and block brake
4. Internal expanding shoe brake
5.
15. Define centrifugal clutch
It works on the principle of centrifugal force i.e the centrifugal force is nicreases with the
increase in speed. It is used when it is required to engage the driven member
automatically after the driving member has attained certain speed.
16. List out the commonly used breaks.
1. Hydraulic brakes: e.g., Pumps or hydrodynamic brake and fluid agitator.
2. Electric brakes: e.g., Eddy current brakes.
3. Mechanical brakes: e.g., Radial brakes and Axial brakes
17. What do you mean by a brake?
Brake is a device by means of which motion of a body is retarded for slowing down (or)
to bring it to rest which works on the principle of frictional force, it acts against the driving
force.
18. Explain. Self-energising.
When moments of efforts applied on the break drum and frictional force are in the same
direction, the breaking torque becomes maximum (frictional force aids the braking action).
In such a case the brake is said to be partially self-actuating or self energising.
19. When is the intensity of pressure acting brake shoe is assumed to be uniform ?
The intensity of pressure is assumed to be constant when the break shoe has small angle
of contact. For large angle of contact, it is assumed that the rate of wear of the shoe remains
constant.
20. Where does the P.I.V. drive system used?
PIV. (Positive Infinitely Variable) drive is used in an infinitely varying speed systems.
21. Why lubrication reduces friction?
In practical all the manting surfaces are having roughness with it. It causes friction. If the
surfaces are smooth then friction is very less. Lubrication smoothens the manting surface by
introducing oil film bet_een it. The fluids are having high smoothness than solids and thus
lubrication reduces friction.
22. What you meant by 'Crowning in pulley' ?
The process of increasing the frictional resistance on the pulley surface is known as
crowning. It is done in order to avoid slipping of the belt.
23. What is meant by initial tension in belts?
In order to' increase the frictional grip between the belt and pulleys, the belt is tightened
up. Due to this the belt gets subjected to some tension even when the pulleys are stationary.
This tension in the belt is called initial tension (To).
24. State the law of belting?
Law of belting states that the centre line of the belt as it approaches the pulley must lie in
a plane perpendicular to the axis of the pulley or must lie in the plane of the pulley,
otherwise the belt will runoff the pulley.
25. What is meant by angle of contact? (Lap angle)
It is the angle made by a common normal drawn to the tangent line at the point of
engagement and at the point of disengagement of the belt on a pulley, at its centre.
26. What is the centrifugal effect on belts?
During operation, as the belt passes over a pulley the centrifugal effect due to its self
weight tends to lift the belt from the pulley surface. This reduces the normal reaction and
hence the frictional resistance.
27. What are the disadvantage of V-belt drive over flat belt?
 1.V- belt cannot be used in large distance. .
2. It is not as durable as flat belt.
3. Since the V belt subjected to certain amount of creep therefore it is not suitable for
constant speed applications such as synchronous machines, and timing devices.
4. It is a costlier system.
28. When is the cross belt used instead of open belt?
1. Cross. belt is used where the direction of rotation of driven pulley is opposite to
driving pulley.
2. Where we need more power transmission there we can use cross belt drive.
29. What is wipping ? How it can be avoided in belt drives?
If the centre distance between two pulleys are t9° long then the belt begins to vibrate
in a direction perpendicular to the direction of motion of belt. This phenomenon is called
as wipping. Wipping can be avoided by using idler pulleys.

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