100 Basic Terms For Mechanical Engineering ( PDF DOWNLOAD )

1.Torque or Turning Force:
It is the total amount of force which is required to create acceleration on moving substance.

Two forces those acts on equally,parallely & oppositely on two separate points of same material.
3.Mass :
The quantity of the matter possessed by a body is called mass. The mass of a body will not change unless the body is damaged and part of it is physically separated. When a body is taken out in a space craft, the mass will not change but its weight may change due to change in gravitational force. Even the body may become weightless when gravitational force vanishes but the mass remain the same.

It is the amount of moving effect which is gained for action of turning force.

It is the force that can prevent equal & opposite force. That means, it is the preventing force. If one force acts on outside of a material, then a reactive force automatically acts to protest that force. The amount of reactive force per unit area is called stress. e.g. Tensile Stress, Compressive Stress, Thermal Stress.

If a force acts on a substance, then in that case if the substance would deform. Then the amount of deformation per unit length of that substance is called strain.

7.Time :
Time is the measure of succession of events. The successive event selected is the rotation of earth about its own axis and this is called a day. To have convenient units for various activities, a day is divided into 24 hours, an hour into 60 minutes and a minute into 60 seconds. Clocks are the instruments developed to measure time. To overcome difficulties due to irregularities in the earths rotation, the unit of time is taken as second which is defined as the duration of 9192631770 period of radiation of the cesium-133 atom.

8.Space :
The geometric region in which study of body is involved is called space. At point in the space may be referred with respect to a predetermined point by a set of linear and angular measurements. The reference point is called the origin and set of measurements as ‘coordinates’. If coordinates involve only in mutually perpendicular directions they are known as Cartesian coordinates. If the coordinates involve angle and distances, it is termed as polar coordinate system.

9.Length :
It is a concept to measure linear distances. The diameter of a cylinder may be 300 mm, the height of a building may be 15 m. Actually metre is the unit length. However depending upon the sizes involved micro, milli or kilo metre units are used for measurement. A metre is defined as length of the standard bar of platinum-iradium kept at the International Bureau of weights and Measures. To overcome difficulties of accessibility and reproduction, now meter is defined as 1690763.73 wave length of krypton-86 atom.

10.Continuum :
A body consists of several matters. It is a well known fact that each particle can be subdivided into molecules, atoms and electrons. It is not possible to solve any engineering problem by treating a body as a conglomeration of such discrete particles. The body is assumed to consist of a continuous distribution of matter. In other words, the body is treated as continuum.

It is one type of device which is being distorted under certain amount of load & also can also go to its original face after the removal of that load.
Its function:
  1. To store energy.
  2. To absorb energy.
  3. To control motion of two elements.

Load per unit deflection. The amount of load required to resist the deflection.

13.Specific Weight:
Weight per unit volume of the fluid.

14.Specific Volume:
Volume per unit mass of the fluid.

15.Specific Gravity:
It is the ratio of specific weight of required substance to specific weight of pure water at 4 degree centigrade temperature.

16.Specific heat:
The amount of heat required to increase 1 unit temperature of 1 unit mass.

Dynamic Viscosity:
The amount of resistance of one layer of fluid over other layer of fluid.

18.Kinematic Viscosity:
It is the ratio of dynamic viscosity to density.

When a body is immersed in a liquid, it is lifted up by a force equal to weight of liquid displaced by the body. The tendency of liquid to lift up an immersed body is buoyancy. The upward thrust of liquid to lift up the body is called buoyancy force.

20.Bernoulli's Equation:
P/γ +V²/2g +Z = Constant
Where, P = pressure,V = velocity,Z = Datumn Head

21.Angular Acceleration : 
The time rate of change of angular velocity.

22.Angular Velocity :
The time rate of change of angular displacement of a point rotating about a fixed axis (expressed in radians per unit time) Angular velocity of a machine part is often expressed in revolutions per minute (RPM) and is denoted by n.

23.Centrifugal Force:
Radial outward force acting on a body moving along a circular path with uniform velocity.

24.Centripetal Force : 
The force that must act radially inward in order to constrain a particle to follow a curved path at uniform velocity.

25.Dead Weight Governor :
The governor in which the radius of the ball path is controlled by levers and weights, the latter being usually attached to the control sleeve.

26.Dynamo-meter :
A device for measuring the forces or couples which tend to change the state of rest or of uniform motion of a body.

27.Floating Link : 
A link in a mechanism which does not have a fixed center of rotation (e.g., coupler in a four bar linkage).

28.Higher Pairs :
Types of kinematic pairs, namely, two elements generally have line or point contact and the pair must be force closed in order to provide completely constrained motion.

29.Involute Teeth : 
The outline of a tooth traced out by a point on a chord unwrapped from a circle (known as base circle).

30.Kennedy's Theorem :
Any three bodies having plane motion relative to one another have three instant centers, and they lie in a straight line.

31.Devices for fluid:
It measures discharge of fluid.
Notches :
It measures discharge of fluid.
Orifice meter:
It measures discharge of fluid.
Pitot tube :
It measures velocity of fluid.

.32.Mach Number:
It is the ratio of the velocity of fluid to the velocity of sound.
M=1 ----------------- Sonic flow
M> (1-6) ----------- Super-Sonic flow
M>6 ---------------- Hyper-Sonic flow

33.Fluid discharge/Fluid flow:
Quantity of fluid flowing per second.
(through a section of pipe/ through a section of channel)
Q=AV where, V= velocity of fluid,A= cross-sectional area of pipe/channel
Note: 1m³ = 1000 L1 cusec = 1 ft³/sec1 ft = 0.3048 m

34.Hydraulic Machine:
Turbine,Pump,Compressor etc.

35.Draft tube:
It attaches with reaction turbine . Its function is to reduce energy loss from reaction turbine & it also reduce pressure at outlet which is must blow the atmospheric pressure.

36. Themodynamics Laws:
Zeroth Law
First Law of Thermodynamic
Second Law of thermodynamic

37.Zeroth Law:
If two body are in thermal equilibrium with a third body then these two body are also in thermal equilibrium with each other.

38.First Law of Thermodynamics:
In a closed system, work deliver to the surrounding is directly proportonal to the heat taken from the surrounding.And also, In a closed system, work done on a system is directly proportonal to the heat deliver to the surrounding.

39.Second Law of Thermodynamics:
It is impossible to make a system or an engine which can change 100 percent input energy to 100 percent output.

40.Newton’s Third Law :
It states that for every action there is an equal and opposite reaction.

41.Newton’s Law of Gravitation :
Every body attracts the other body. The force of attraction between any two bodies is directly proportional to their masses and inversely proportional to the square of the distance between them.

42.Law of Transmissibility of Force :
According to this law the state of rest or motion of the rigid body is unaltered if a force acting on the body is replaced by another force of the same magnitude and direction but acting anywhere on the body along the line of action of the replaced force.

43.Unit :
The qualitative description of physical variable is known as dimension while the quantitative description is known as unit.

44.Scalar :
A quantity is said to be scalar, if it is completely defined by its magnitude alone.

45.Vector :
A quantity is said to be vector if it is completely defined only when it’s magnitude as well as direction are specified.

It is a thermodynamic property.

ds = dq/T
where, ds = change of entropy, dq = change of heat, T = Temperature.
In adiabatic process, entropy can not change. Actually,lacking or mal-adroitness of transferring energy of a system is entropy.

47.Calorific Value of fuel:
It us the total amount of heat obtained from burning 1 kg solid or liquid fuel.

It is a clossed vessel which is made of steel. Its function is to transfer heat to water to generate steam.

It is a part of boiler. Its function is to heat feed water which is supplied to boiler.

It is a part of boiler. Its function is to increase temperature of steam into boiler.

It is a part of boiler. Its funtion is to preheats the air to be supplied to furnace and it recover heat from exhaust gas.

52.Boler Draught:
It is an important term for boiler. It is the difference of pressure above and below the fire grate. This pressure difference have to maintain very carefully inside the bolier. It actually maintaind the rate of steam generation. This depends on rate of fuel burning. Inside the boiler rate of fuel burning is maintained with rate of entry fresh air. If proper amount of fresh air never entered into the boiler, then proper amount of fuel inside the boiler never be burnt. So, proper fresh air enters into the boiler only by maintaining boiler draught.

Nozzle is a duct of varying cros-sectional area. Actually, it is a passage of varying cross-sectional area. It converts steam's heat energy into mechanical energy. It is one type of pipe or tube that carrying liquid or gas.

It is the process of removing burnt gas from combustion chamber of engine cylinder.

55.Crank Throw :
This is the distance between the Center of Crankshaft and Center of Crank pin. Hence the distance will be equal to half the Stroke Length.

56.Push Rods :
The mechanical linkage between the camshaft and valves on overhead valve engines with the camshaft in the crankcase.

Actually, power output of engine depends on what amount of air enter into the engine through intake manifold. Amount of entry aiy if increased, then must be engine speed will increased. Amount of air will be increased by increasing inlet air density. The process of increasing inlet air density is supercharging. The device which is used for supercharging is called supercharger.Superchargeris driven by a belt from engine crakshaft. It is installed in intake system.

Turbocharging is similar to the supercharging. But in that case tubocharger is installed in exhaust system whereas supercharger is installed in intake system. Turbocharger is driven by force of exhaust gas. Generally, turbocharger is used for 2-stroke engine by utilizing exhaust energy of the engine, it recovers energy otherwise which would go waste.

Its function id to regulate mean speed of engine when there are variation in the load. If load incrases on the engine, then engine's speed must decrease. In that case supply of working fluid have to increase. In the otherway, if load decrease on the engine, then engine' speed must increase. In that case supply of working fluid have to decrease.Governor automatcally, controls the supply of working fluid to the engine with varying load condition.

It is the one of the main parts of the I.C. engine. Its main function id to store energy in the time of working stroke or expansion stroke. And, it releasesenergy to the crankshaft in the time of suction stroke, compression stroke & exhaust stroke. Because, engine has only one power producing stroke.

61.Rating of fuel:
S.I. Engine:Octane number. Octane number indicates ability of fuel to resist knock.
C.I. Engine:Cetane Number. Cetane number indicates ability of ignition of diesel fuel. That means, how much fast ignites diesel fuel.

62. Stoichiometric ratio:
It is the chemically correct air-fuel ratio by volume. By which theoratically sufficient oxygen will be gotten to burn all combustible elements in fuel completely.

63.Heat Transfer:
It is a science which deals with energy transfer between material bodies as a result of temperature difference.There are three way to heat transfer such as-Conduction Convection Radiation.

64.Air Velocity:
The speed of air flow on the surrounding is know as Air Velocity. The Air Velocity is an important factor in Thermal Comfort.If the Air flows in warm or humid conditions can increases the heat loss through the convection without any change in air temperature.
Where as in case cold conditions if air flows then perceived as a draught as people are particularly sensitive to these movements.

65.Thermal Conductivity:
It is the quantity of heat flows between two parts of solid material by conduction. In this case following consideration will be important fact-
Time------ 1 sec
Area of that solid material-------- 1 m²
Thickness of that solid material------ 1m
Temperature difference between two parts of that material------ 1k

Humidity referred as the amount of water vapor in the air.When the water heated up then the water will be evaporated to surrounding atmosphere in gaseous stage.Then the water levels in air will be increased these is know as Humidity. Higher humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin.

67.Metabolic heat:

Heat produced by human body is know as Metabolic heat. The Work Rate/Metabolic is an very important factor in Humans Thermal Comfort. Because when we work more heat we will release. If we more heat we released , the more heat needs to be lost so our body doesn't get  overheated.

68.Heat Exchanger:
It is one type of device which can transfer heat from one fluid to another fluid. Example- Radiator, intercooler, preheater, condenser, boiler etc.

It is the process of removing heat from a substance. Actually, extraction of heat from a body whose temperature is already below the temperature of its surroundings.

70.Temperature :
Temperature is defined as it is a physical or a thermal state of a body which distinguishes a hot body from a cold body. Temperature can mean different things in different situations. The temperature of a body is proportional to the stored molecular energy i.e., The average molecular kinetic energy of the molecules in a system. And also a particular molecule does not have a temperature, it has energy. The gas as a system has temperature.

71.Radiant Heat:
The Radiant Heat is derived by the average temperature of the objects and surfaces that surround us, and it depends on the material’s ability to absorb or emit heat.

72. One (1) tonne of refrigeration:
It is amount of refrigeration effect or cooling effect which is produced by uniform melting of 1 tonne ice in 24 hours from or at 0 degree centigrade or freezing 1 tonne water in 24 hours from or at 0 degree centigrade.

It is the addition of moisture to the air without change dry bulb temperatur.

74. Dehumidification:
It is the removal of moisture from the air without change dry bulb temperature.

75.Gear Train:
Meshing of two or more gear. It can transmit power from one shaft to another shaft.

76.Heat Treatment:
Operation involving heating and cooling of a metal in solid state for obtaining desirable condition without being changed chemical composition.Its object-increase hardness of metal.increase quality of metal ( heat, corrosion,wear resistance quality )improve machinability.

77.Ferrous Metal:
1. Cast Iron - (2-6.67)%C, Si, Mn, P, S
2. Steel - (0-2)%C
3. Wrought Iron - 99.5% Fe

78.Non-Ferrous Metal:
1. Brass - (Cu+Zn)
2. Bronze -
(Sn+Cu) ------ Tin Bronze
(Si+Cu) ------- Silicon Bronze
(Al+Cu) ------- Aluminium Bronze

It is the difference between basic dimension of mating parts. That means, minimum clearance between mating parts that can be allowed.

80.Upper Deviation:
The algebraic difference between the maximum limit and the basic size is called as Upper Deviation.

81.Lower Deviation:
The algebraic difference between the minimum limit and the basic size is called as Lower Deviation.

It is the difference between upper limit of dimension. It is also the permissible variation above and below the basic size. That means maximum permissible variation in dimensions.

It is the difference in size between mating parts. That means, in that case the outside dimension of the shaft is less than internal dimension of the hole.

It is the ability to resist deformation.

It is the property to resist fracture.

When a material is subjected to repeated stress below yield point stress, such type of failure is fatigue failure.

If an input is given to the measurement system and the output deviates from the given input, the corrections are needed to be made in the instrument and then measure the output. This is called “Calibration”.

This is defined as the ratio of change in the output signal to the change in the input.


The ease with which the readings of a measuring instrument can be done.

90.Nuclear Fission:
It is a nuclear reaction by which one big nucleous divided into two or more nucleous.

91.Nuclear Fussion:
It is also a nuclear reaction by which one big nucleous will produced by adding two small nucleous.

It is the process of joining two similar or dissimilar metal by fusion.

93.Arc Welding:
* need D.C current
* produced (6000-7000) Degree Centegrade Temperature

94.Gas Welding :
* Oxy - acetylene flame join metals
* Oxygen & acetylene gas works
* produced 3200 Degree Centegrade Temperature

95.Machine Tool:
It is the power driven tool. It cut & form all kinds of metal parts.
Example - 
  1. Lathe
  2. Drill Press
  3. Shaper
  4. Planer
  5. Grinding
  6. Miling
  7. Broaching
  8. Boring

96.Cutting Tool:
Tool Materials for Cutting Tool:
1. High Carbon Steel
2. High Speed Steel (W+Cr+V)
3. Carbide (W Carbide+Ti Carbide+Co Carbide)

It is the method of dividing periphery of job into equal number of division. Actually, it is the process of dividing circular or other shape of workpiece into equal space, division or angle.

It is one type of device which hold & locate work piece and also guide & control cutting tool. It uses in drilling, reaming and tapping.

It is one type of device which hold and locate work piece. It uses in miling, grinding, planning & turning.

Forging & Casting :Forging is the application of thermal and mechanical energy to converting metal into desire shape by applying pressure and with or without heat.And Casting is the process where metal is heated until molten. While in the molten or liquid state it is poured into a mold or vessel to create a desired shape.

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