A force exerted on a body can cause a change in either the shape or the motion of the body. The unit of force in SI system is the newton (N) and CGS system is dyne. No solid body is perfectly rigid and when forces are applied to it, changes in dimensions occur. Such changes are not always perceptible to the human eye since they are negligible. For example, the span of a bridge will sag under the weight of a vehicle and a spanner will bend slightly when tightening a nut. It is important for civil engineers and designers to appreciate the effects of forces on materials, together with their mechanical properties of materials.
There are three main types of mechanical forces that can act on a body. They are:
  1. Tensile force
  2. Compressive force and
  3. Shear force

1. Tensile force

Tensile force that tends to stretch a material, as shown in the figure 1 below.

Figure 1: Tensile force
For example,
  1. Rubber bands, when stretched, are in tension.
  2. The rope or cable of a crane carrying a load is in tension.
  3. When a nut is tightened, a bolt is under tension.
A tensile force will increases the length of the material on which it acts.

2. Compressive force

Compressive force that tends to squeeze or crush a material, as shown in the figure 2 below.

Figure 2: Compressive force
For example,
  1. A pillar supporting a bridge is in compression.
  2. The sole of a shoe is in compression.
  3. The jib of a crane is in compression.
compressive force will decrease the length of the material on which it acts.

3. Shear force

Shear force that tends to slide one face of the material over an adjacent face.

Figure 3: Shear force
For example,
  1. A rivet holding two plates together is in shear if a tensile force is applied between the plates as shown in Figure 3.
  2. A guillotine cutting sheet metal, or garden shears, each provide a shear force.
  3. A horizontal beam is subject to shear force.
  4. Transmission joints on cars are subject to shear forces.
shear force can cause a material to bend, slide or twist.


Comparison between Fire Tube and Water Tube Boiler can be done in 14 aspects. Those aspects are operating pressure, passage of material type in tubes, rate of steam generation, handling of load fluctuation, floor area requirement, efficiency, operator skills, design, maintenance cost are listed below in the tabular form.


Mechanical properties helps us to measure how materials behave under a load. Mechanical properties of materials are mentioned below.

Elastic Material:

A material which regains its original size and shape on removal stress is said to be elastic stress.

Plastic material:

A material which can undergo permanent deformation without rupture aid to be plastic material. This property of the material is known as plasticity. Plasticity is important when a material is to be mechanically formed by causing the material to flow.

Ductile Material:

A material which an undergo considerable deformation without rupture is said to be ductile material. The major portion of deformation is plastic.

Brittle Material:

A material which ruptures with little or no plastic deformation is said to brittle materials.

Set of Permanent set:

The deformation or strain remaining in a body after removal of stress is known as permanent set. This is due to elastic property of material.

Elastic limit:

The greatest stress that a material can take without permanent set on the removal of stress is known as elastic limit.

Proportionality limit:

The greatest stress that a material can take without deviation from straight line between stress and strain is known as proportionality limit.

Endurance limit or Fatigue limit:

The greatest stress, applied infinite number of times, that a material can take without causing failure is known as endurance limit or fatigue limit.

Ultimate Strength:

The maximum stress material can take is known as ultimate strength. Ultimate strength is equal to maximum load divided by original area of cross section.

Modulus of Resilience:

The energy stored per unit volume at the elastic limit is known as modulus of resilience.

Modulus of Toughness:

The amount of work required per unit volume to cause failure, under static loading, is called modulus of toughness.

Modulus of Rupture:

The ultimate strength in flexure or torsion is known as modulus of rupture.

Strain hardening:

The increase in strength after plastic zone due to rearrangement of molecules in the material.

Proof stress:

The stress which is just sufficient to cause a permanent set(elongation) equal to a specified percentage of the original gauge length.

Elastic Strain:

Elastic strain is a dimensional change that occur in a material due to the application of loads and disappears completely on the removal of the loads.

Plastic Strain:

It is a dimensional change that occurs in a material due to application of the loads and does not disappear after the removal of the loads.

Ductility and malleability:

The plastic response of material to tensile force is known as ductility and plastic response to compression force is known as malleability. The elongation and reduction of area of test piece tested to failure in tension are generally taken as measures of ductility of material.


The long term deflection due to sustained (constant) loads.

Factor of Safety:

Factor of safety is defined as follows
For Ductile materials,
F.O.S = yield stress / working stress
For Brittle materials,
F.O.S = ultimate stress / working stress

Margin of Safety:

Margin of safety = Factor of safety – 1


The sidewall of tyre provides the information about the tyre including the specifications, the brand, etc. All the codes on tyres are standardized and recognized by all tyre manufacturers worldwide

Meaning of codes marked on tyres:
  1. Tyre width (in mm)
  2. Aspect Ratio
  3. Rim Diameter (in inches)
  4. Load Index
  5. Speed rating
Specifications of tyre marked on sidewall on above image as 235/45R17 97W
The ‘235’ indicates the section width of the tyre in millimeters.
The ’45’ tells the ‘profile’ of the tyre, or the width of the tyre compared to its height. It is expressed in percentage. (45%, in this case).
The ‘R17′ indicates the size (in inches) of the wheel rim to which the tyre is designed to be fitted.
The ’97’ indicates the tyre’s load index, and
The ‘W’ denotes the speed rating.
Load Index:
Load index corresponds to the load capacity . Commonly chosen load index values of automobiles are shown below in image.

Speed Rating:
The Speed rating of a tyre is the maximum speed at which the tyre can carry a load corresponding to its load index is an assigned letter ranging from J to Z that corresponds to the reference maximum speed at the associated load index. Refer to the speed rating table below.


cam is a rotating or sliding piece in a mechanical linkage that drives a mating component known as a follower. From a functional viewpoint, a cam-and-follower arrangement is very similar to the linkages. The cam accepts an input motion (rotary motion or linear motion) and imparts a resultant motion (linear motion or rotary motion) to a follower.

Cam Nomenclature

FIGURE 1 CAM nomenclature
Cam profile: Cam profile is outer surface of the disc cam.
Base circle: Base circle is the smallest circle, drawn tangential to the cam profile.
Trace point: Trace point is a point on the follower, trace point motion describes the movement of the follower.
Pitch curve: Pitch curve is the path generated by the trace point as the follower is rotated about a stationery cam.
Prime circle: Prime circle is the smallest circle that can be drawn so as to be tangential to the pitch curve, with its centre at the cam centre.
Pressure angle: The pressure angle is the angle between the direction of the follower movement and the normal to the pitch curve.
Pitch point: Pitch point corresponds to the point of maximum pressure angle.
Pitch circle: A circle drawn from the cam center and passes through the pitch point is called Pitch circle.
Stroke: The greatest distance or angle through which the follower moves or rotates.

Types of Cams

Various custom cams
Cams can be classified into the following three types based on their shapes. They are:
  1. Plate or disk cams: Plate or disk cams are the simplest and most common type of cam. A plate cam is illustrated in figure 3 (a). This type of cam is formed on a disk or plate. The radial distance from the center of the disk is varied throughout the circumference of the cam. Allowing a follower to ride on this outer edge gives the follower a radial motion.
  2. Cylindrical or drum cam: A cylindrical or drum cam is illustrated in figure 3 (b). This type of cam is formed on a cylinder. A groove is  cut into the cylinder, with a varying location along the axis of rotation. Attaching a follower that rides in the groove gives the follower motion along the axis of rotation.
  3. Linear cam: A linear cam is illustrated in figure 3 (c). This type of cam is formed on a translated block. A groove is cut into the block with a distance that varies from the plane of translation. Attaching a follower that rides in the groove gives the follower motion perpendicular to the plane of translation.

FIGURE 3 Cam types

Types of Followers

Followers are classified based on their motion, position and shape. The details of followers classifications are shown in the figure 4 and discussed below

FIGURE 4 Follower types
1. Based on Follower Motion
Based on the follower motion, followers can be classified into the following two categories:
(i). Translating followers are constrained to motion in a straight line and are shown in figure 4 (a) and 4 (c).
(ii). Swinging arm or pivoted followers are constrained to rotational motion and are shown in figure 4 (b) and 4 (d).
2. Based on Follower Position
Based on the follower position, relative to the center of rotation of the cam, is typically influenced by any spacing requirements of the machine. The position of translating followers can be classified into the following two categories:
(i). An in-line follower exhibits straight-line motion, such that the line of translation extends through the center of rotation of the cam and is shown in figure 4 (a).
(ii). An offset follower exhibits straight-line motion, such that the line of the motion is offset from the center of rotation of the cam and is shown in figure 4 (c).
In the case of pivoted followers, there is no need to distinguish between in-line and offset followers because they exhibit identical kinematics.
3. Based on Follower Shape
Finally, the follower shape can be classified into the following four categories:
(i). A knife-edge follower consists of a follower that is formed to a point and drags on the edge of the cam. The follower shown in figure 4 (a) is a knife-edge follower. It is the simplest form, but the sharp edge produces high contact stresses and wears rapidly. Consequently, this type of follower is rarely used.
(ii). A roller follower consists of a follower that has a separate part, the roller that is pinned to the follower stem. The follower shown in figure 4 (b) is a roller follower. As the cam rotates, the roller maintains contact with the cam and rolls on the cam surface. This is the most commonly used follower, as the friction and contact stresses are lower than those for the knife-edge follower. However, a roller follower can possibly jam during steep cam displacements.
(iii).  A flat-faced follower consists of a follower that is formed with a large, flat surface available to contact the cam. The follower shown in figure 4 (c) is a flat-faced follower. This type of follower can be used with a steep cam motion and does not jam. Consequently, this type of follower is used when quick motions are required. However, any follower deflection or misalignment causes high surface stresses. In addition, the frictional forces are greater than those of the roller follower because of the intense sliding contact between the cam and follower.
(iv).  A spherical-faced follower consists of a follower formed with a radius face that contacts the cam. The follower shown in figure 4 (d) is a spherical-face follower. As with the flat-faced follower, the spherical- face can be used with a steep cam motion without jamming. The radius face compensates for deflection or misalignment. Yet, like the flat-faced follower, the frictional forces are greater than those of the roller follower.


The term “automotive night vision” refers to a number of systems that help increase driver awareness when it’s dark out. These systems extend the perception of the driver beyond the limited reach of the headlights through the use of thermographic cameras, infrared lights, heads up displays, and other technologies. Since automotive night vision can alert drivers to the presence of potential hazards before they become visible, these systems can help prevent accidents.

How Does Night Vision Work in Cars?

Automotive night vision systems are broken into two basic categories, which are referred to as active and passive. Active night vision systems uses infrared light sources to illuminate the darkness, and passive systems rely on the thermal radiation that is emitted from cars, animals, and other potential hazards. The systems both rely on infrared data, but each one has its own benefits and drawbacks.

Active Automotive Night Vision Systems

Active systems are more complex than passive systems because they use infrared light sources.
Since the infrared band falls outside the visible spectrum, these light sources don’t cause oncoming drivers to suffer from temporary night blindness like high beam headlights can. That allows the infrared lights to illuminate objects that are significantly further away than headlights are able to reach.
Since infrared light isn’t visible to the human eye, active night vision systems use special cameras to relay the extra visual data. Some systems use pulsed infrared lights, and others use a constant light source. These systems don’t work very well in adverse weather conditions, but they do provide high contrast images of vehicles, animals, and even inanimate objects.

Passive Automotive Night Vision Systems

Passive systems don’t use their own light sources, so they rely on thermographic cameras to detect thermal radiation. This tends to work very well with animals and other vehicles since they emit a lot of thermal radiation. However, passive systems have trouble picking up inanimate objects that are about the same temperature as the surrounding environment.
The range of passive night vision tends to be significantly higher than the range of active night vision, which is due to the limited power of the light sources used by the latter systems. The image quality produced by the thermographic cameras also tends to be poor when compared to active systems, and they don’t work very well in warm weather.

How Does Infrared or Thermographic Information Help Me See?

There are a number of types of night vision displays that can relay infrared or thermographic information to the driver. The earliest night vision systems used heads up displays, which projected warnings and alerts on the windshield within the driver’s field of vision. Other systems use an LCD that's mounted on the dash, in the instrument cluster, or integrated into the head unit.


Air Bags:-
An airbag is a type of vehicle safety device and is an occupant restraint system. The airbag module is designed to inflate extremely rapidly then quickly deflate during a collision or impact with a surface or a rapid sudden deceleration. 

The purpose of the airbag is to provide the occupants a soft cushioning and restraint during a crash event to prevent any impact or impact-caused injuries between the flailing occupant and the interior of the vehicle. The airbag provides an energy absorbing surface between the vehicle's occupant and a steering wheel, instrumental panel, A-B-C- structural body frame pillars, headliner and windshield/windscreen.

There are three parts to an airbag that help to accomplish this feature:
>The bag itself is made of a thin, nylon fabric, which is folded into the steering wheel or dashboard or, more recently, the seat or door.
>The sensor is the device that tells the bag to inflate. Inflation happens when there is a collision force equal to running into a brick wall at 10 to 15 miles per hour (16 to 24 km per hour). A mechanical switch is flipped when there is a mass shift that closes an electrical contact, telling the sensors that a crash has occurred. The sensors receive information from an accelerometer built into a microchip.

>The airbag's inflation system reacts sodium azide (NaN3) with potassium nitrate (KNO3) to produce nitrogen gas. Hot blasts of the nitrogen inflate the airbag.



1) Ideal fluid : This fluid is incompressible and possesses no viscosity. Such a fluid is only an imaginary fluid. All existing fluids have some viscosity.

 (ii) Real fluid : A fluid that possesses viscosity is known as a real fluid. In actual practice, all fluids are real fluids. 

(iii) Newtonian fluids : A real fluid in which the shear stress is directly proportional to the rate of shear strain (or velocity gradient) is called Newtonian fluid.

 iv) Non-Newtonian fluids : A real fluid in which the shear stress is not proportional to the rate of shear strain (or velocity gradient) is called non-Newtonian fluid. 

v) Ideal plastic fluid : A fluid in which the shear stress is more than the yield value and the shear stress is proportional to the rate of shear strain (or velocity gradient) is called ideal plastic fluid.


1. Incompressible flow-M less than 0.3 

2. Compressible subsonic flow-M between 0.3 and 1 

3. Transonic flow-M ranging between values less than 1 and more than 1 

4. Supersonic flow-M greater than 1 but less than 5 

5. Hypersonic flow - M greater than 5


Hydraulic turbine which are generally known as water turbine used to convert hydraulic energy or we can say that energy of water (kinetic and pressure energy of water)  into mechanical energy. This mechanical energy is further used to drive a generator which converts it into electrical energy. The basic concept of this type of turbine is that water flowing from a dam generates a pressure force while passing through the turbine. This pressure force use to rotate the turbine which further rotate the generator and convert hydraulic energy into electrical energy.

Hydraulic Turbine: Working, Types, Advantages and Disadvantages

Working Principle:

According to Newton's law a force is directly proportional to the change in momentum. So if there is any change in momentum of fluid a force is generated. In the hydraulic turbine blades or bucket (in case of Pelton wheel) are provided against the flow of water which change the momentum of it.  As the momentum is change a resulting pressure force generated which rotate the rotor or turbine. The most important phenomenon is the amount of change in momentum of water which is directly proportional to force. As the change in momentum high the force generated is high which increase the energy conversion. So the blade or buckets are designed so it can change maximum momentum of water. This is the basic principle of turbine. These turbines are used as hydro electric power plant.

Hydraulic Turbine: Working, Types, Advantages and Disadvantages


The hydraulic turbine can be classified according to the energy available at inlet, direction of flow of water, Specific speed, head available at inlet etc. These all types are described as below.

According to Type of Energy Available at Inlet:

Impulse Turbine:
Impulse turbine is those turbines which are use impulse energy or we can say kinetic energy of water to rotate the turbine. In this type of hydraulic turbine all pressure head or pressure energy is converted into velocity head or kinetic energy at the inlet of turbine by using nozzle. This high speed water jet strikes the blade or bucket of turbine which develop a force which rotate it. Only kinetic energy changes at the inlet and outlet of turbine and the pressure of water remain same. This kind of turbine is known as impulse turbine. There are various design available of impulse turbine but the Pelton wheel most suited for it. These are generally high head and low discharge hydraulic turbine.

Reaction Turbine:
As the name implies these turbines is used pressure energy of water to rotate the turbine. In practically no turbine can purely used pressure energy. So it used both its pressure energy and kinetic energy. These turbines rotate partially due to impulse action and partially due to pressure change over the runner blades. The water flow over blades covert both its kinetic energy as well as pressure energy into force and rotate the turbine. The change in pressure energy of water known as degree of reaction of the turbine. So it is known as reaction turbine. They are generally low head, high discharge turbine.

According to Direction of Flow:

Tangential Flow Turbine:
In this hydraulic turbine the water flow through tangent of runner. The water jet strikes the runner tangentially and rotates the turbine. Example Pelton wheel turbine

Hydraulic Turbine: Working, Types, Advantages and Disadvantages
Pelton Turbine

Radial Flow Turbine:
In this type of turbine the water flows in radial direction. This is subdivided into two types. The first one is known as inward radial flow in which the water flows from periphery to the center. Example Francis turbine.
Second one is known as outward flow radial turbine in which water flow towards periphery from center.

Hydraulic Turbine: Working, Types, Advantages and Disadvantages
Francis Turbine
Axial Flow Turbine:
In this hydraulic turbine, the water flow from the axis of turbine. Example Kaplan turbine

Hydraulic Turbine: Working, Types, Advantages and Disadvantages
Kaplan Turbine

Mixed Flow Turbine:
When the water enters the turbine radically and exit axially or vice versa, it is known as mixed flow turbine.

According to Head of Water Available at Inlet:

High Head Turbine:
 If the water level or water reservoir is above 150 - 2000 m from the axis of turbine, it is known as high head turbine. It is best suited for impulse turbine.

Medium Head Turbine:
If the water level varies from 30 -130 m from the axis of the turbine, it is known as medium head turbine. Example Francis Turbine

Low Head Turbine:
If the water level is below 30 meter from the axis of turbine, it is known as low head turbine. These hydraulic turbine required high discharge rate to work efficiently. Example Kaplan turbine.

According to Specific Speed of Turbine:

Low Specific Speed Turbine:
If the specific speed is less than 50 the turbine is considered as low specific speed turbine. Example Pelton wheel

Medium Specific Speed Turbine:
If the specific speed is between 50 - 150, it is considered as medium specific speed turbine. Example Francis Turbine

High Specific Speed Turbine:
If the specific speed of turbine is above 250 it is known as high specific speed turbine. Example Kaplan Turbine

Advantages and Disadvantages:

Hydro power plant or we can say that hydraulic turbines are widely used form the last decades. It is an efficient renewable energy source. There are many up and downs in every project so there are also have many advantages and disadvantages which are describe below.


  • It is a renewable energy source. Water energy can be used again and again.
  • The running cost of turbine is less compare to other.
  • It has high efficiency.
  • It can be control fully. The gate of dam is closed when we does not need electricity and can be open when we needed.
  • Dams are used from very long time so it can be used for power generation.
  • It does not pollute environment.
  • It is easy to maintain.
  • The dam constructed for hydraulic turbine can become a tourist place.


  • Initial cost is very high. It takes several decades to become profitable.
  • It can destroy the natural environment at site. Large dam cause big geological damages.
  • It can develop at only few sites where proper amount of water is available.


Production Engineering Questions and Answers
1-The reaction, in which one solid phase splits into two solid phases on heating, is called
(A) eutectic
(B) peritectic
(C) eutectoid
(D) peritectoid

2-Chemical embossing process is basically
(A) an etching process
(B) electroplating process
(C) galvanising process
(D) engraving process

3-In Taylor’s tool life equation, VTn=C, index ‘n’ depends upon
(A) material of work piece
(B) condition of machine
(C) material of tool
(D) coolant used

4-Time taken to drill a hole through a 25mm thick plate at 300rpm at a feed rate of 0.25mm/revolution will be
(A) 20 sec
(B) 0.2 sec
(C) 18.75 sec
(D) 180 sec

5-The numerical control system which is applicable to a milling machine is called the
(A) point to point system
(B) continuous path system
(C) straight cut system
(D) contouring system

6-Which of the following tools are harder and more wear resistant than tungsten carbide but are weaker in section?
(A) low carbon steel tools
(B) high carbon steel tools
(C) HSS tools
(D) Ceramic tools

7-The following non-conventional method of machining essentially requires electrolyte

8-In resistance welding, voltage used for heating is
(A) 1V
(B) 10V
(C) 100V
(D) 1000V

9-Which colour of flame represent highest temperature?
(A) blue
(B) bright red
(C) dark yellow
(D) white

10-Kerosene is required while machining
(A) Aluminium
(B) Magnesium alloy
(C) Brass
(D) Low carbon steel

11-18-4-1 High speed steel has
(A) 1% chromium
(B) 4% tungsten
(C) 18% vanadium
(D) 0.7% carbon

12-When the movement of a work piece against a rotating cutter is involved in a machining operation which machine tool is used
(A) Milling machine
(B) Lathe machine
(C) Drilling machine
(D) Shaper machine

13-Most commonly used in a gas metal arc welding (GMAW) process is
(A) Oxygen
(B) Acetylene
(C) Hydrogen
(D) Carbon dioxide

14-In oxy-acetylene welding process, the role of oxygen is
(A) Act as a fuel
(B) Acts as a coolant
(C) Chemically combines with acetylene to produce heat
(D) Acts as a flux

15-The percentage of carbon in pig iron is
(A) 0.5 – 1%
(B) 1 – 1.5%
(C) 2 – 3%
(D) 3.5 – 4.5%

16-The main function of the inert gas in MIG welding is to
(A) make cleaning of the weld easy
(B) keep contaminants out and prevents oxidation in the weld
(C) reduces heat and stress in the weld
(D) reduce grain growth

17-The abrasive slurry used in ultrasonic machining contains fine particles of
(A) Aluminium oxide
(B) Boron carbide
(C) Silicon carbide
(D) All of these

18-The cutting fluid mostly used for machining steel is
(A) Water
(B) Soluble oil
(C) Dry
(D) Heavy oils

19-The angle on which the strength of the tool depends is
(A) Rake angle
(B) Cutting angle
(C) Clearance angle
(D) Lip angle

20-Structural sections such as rails, angles and I beams are made by
(A) Hot rolling
(B) Hot drawing
(C) Hot piercing
(D) Hot extrusion

1-(D), 2-(D), 3-(C), 4-(A), 5-(C), 6-(D), 7-(B), 8-(A), 9-(A), 10-(A), 11-(D), 12-(A), 13-(D), 14-(C), 15-(D), 16-(B), 17-(D), 18-(D), 19-(A), 20-(A)