Basic Definitions

Basic Definitions

Mass

It is quantity of matter contained in a body. It does not depend upon gravitational force. The 

fundamental unit of mass is the Kilogram (kg).

Weight

Weight is the force exerted by gravity. Weight of body is dependent upon gravitational force, so it is 

not constant.

Weight = Mass x Gravitational acceleration

W =m g

Force

It is push or pull acting on a body which changes or tends to change the state of rest or uniform motion of

the body.

As per Newton's second law of motion

Force ∝ acceleration

F= m a 

In SI unit (International system), unit of mass is kg and unit of acceleration is m/s2 and unit of the force is

Newton (N).

When m = 1 kg, and a = 1 m/s


then F = 1 N.

1 N: When unit mass is given unit acceleration then the force produced is 1 N.

Pressure

It is the force exerted by fluid (liquid or gas) on unit area. It is a property of fluid.

 Pressure=Force/Area=N/m²


The unit of pressure is known as Pascal (Pa) or N/m2

1 Pa = 1 N/m2

Other commonly used units of pressure are:

1 kPa (Kilo Pascal) = 103 Pa

1 Mpa (Mega Pascal) = 106 Pa

1 bar = 105 Pa

Measurement of pressure:

Pressure is measured by Barometer, Pressure gauges and manometers.

Atmospheric pressure:

It is the pressure exerted by atmosphere. The atmospheric pressure varies from place to place. At sea level

the pressure is,

1 standard atmosphere (atm) = 101325 Pa = 1.01325 bar

Barometer is used to measure atmospheric pressure.

Standard atmospheric pressure:

It is a pressure of atmospheric air at mean sea level. It is defined as “The pressure produced by a mercury

column of 760 mm high having a density of 13595.09 kg/m3 and acceleration due to gravity being 9.80665

m/s2.”

Now,pressure=§×g×h


=13595.09 9.80665 760 10


 1.01325 10

N/m2 = 1.01325 bar

Gauge pressure:

The pressure relative to the atmosphere is called gauge pressure. This pressure is measured by pressure gauge.

Absolute pressure

It is the pressure measured with reference to absolute zero pressure. It is the pressure related to perfect

vacuum.

Mathematically, Absolute pressure = Atmospheric pressure + Gauge pressure

Vacuum:

The pressure below atmospheric pressure is called vacuum. A perfect vacuum is obtained when absolute

pressure is zero; at this instant molecular momentum is zero. The relation between different pressures is given

in Fig. 2.



Work

Work is said to be done when a force moves the object through a distance in direction of force.

Hence, Work = Force x Distance moved into direction of force.

W =F× d 

W =F/A ×(A×d)

W=p×V

Power

Power is defined as the rate of doing work OR the power is work done per unit time.

Mathematically,

Power=Workdone Power/time


and unit of power is Joule/second.

In SI unit Joule/second is called Watt (W)

Watt is very small unit, so another larger units are megawatt (MW), Kilowatt (kW).

Energy

Energy means capacity for doing work.

The unit of energy is the unit of work i.e. Joule. In our daily life unit of energy use is Kilowatt hour (kWh).

Forms of energy:-

The different forms of energy are;

(1) Mechanical energy (2) Thermal or heat energy

(3) Chemical energy (4) Electrical energy-

(5) Nuclear energy

“Energy can neither be created nor be destroyed but the total amount of energy remains constant. It is

possible to convert one form of energy into another form of energy.” This is called the law of conservation of

energy.




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