IEMDaily - Video Lecture Notes

Definition

Conversion of units between two systems of units

Some conversion formulae between systems are listed below:

$Q u a n t i t y$	$S I$	$C G S$	$M K S$	$F P S$
Length	1m	1 cm = 0.01 m	1m	1 foot = 0.3048 m
Mass	1 kg	1 g = 0.001 kg	1 kg	1 pound = 0.4536 kg
Time	1 s	1 s	1 s	1 s

Example:
If mass of a man is

200

pounds, its

M K S

weight can be found as follows:

1 p o u n d = 0.4536 k g

200 p o u n d = 0.4536 \times 200 = 90.72 k g

Definition

Good unit

The product of magnitude of a quantity and numerical value of its corresponding unit. A good unit has the property that the magnitude in the corresponding unit system is neither too large nor too small and the values are easy to compare. For example, it is convenient to express the distance between two cities in km rather than in cm.

Example

SI system of units

The International System of Units (SI) defines seven units of measure as a basic set from which all other SI units are derived. The SI base units and their physical quantities are:

1. meter for length
2. kilogram for mass
3. second for time
4. ampere for electric current
5. kelvin for temperature
6. candela for luminous intensity
7. mole for the amount of substance

Definition

Identification of units and quantities from each other

It is possible to define a unit for a given physical quantity. For example, length and distance can have the units of meter, inch, miles, light year, etc.
It is possible to estimate the physical quantity from its units. However, it should be noted that multiple quantities can have the same unit and hence this estimate is not accurate. So, if a quantity is given as

1 J

, then it can represent work or some form of energy.

Example

Common units for measurement in daily life

1 Feet

= 30.48 c m

1 Sq.feet

= 30.48 c m \times 30.48 c m = 929.0304 s q . c m

1 Ground

= 2400 s q . f e e t

1 Kuzhi

= 145.2 s q . f e e t

1 Cent

= 435. 60 s q . f e e t

1 Acre

= 43560 s q . f e e t = 300 K u z h i = 100 C e n t

In practice, we use only rounded off values of the above measurements.

Example

Common Measurement units used in daily life

Quantity	Units
Length	Metre
	1 Decimeter = 0.1m
	1 centimeter = 0.01m
	1 kilometer = 1000m
Volume	Cubic meter $(m^{3})$
	1 Cubic centimeter = $(c m^{3})$ = 0.000001 $m^{3}$
Mass	1 Kilogram = 1000 gram
Time	1 minute = 60sec

Definition

Physical Quantity

Physical quantity: A physical quantity is a quantity in physics that can be measured, thus a physical property that can be quantified. Examples of physical quantities are mass, amount of substance, length, time, temperature, electric current, light intensity, force, velocity, density, and many others.

Definition

System of units

In mechanics, length, mass and time are three fundamental quantities. For the units of these basic quantities, following systems have been used:
(1) C.G.S. System: In this system, the unit of length is centimetre, unit of mass is gram and the unit of time is second.
(2) F.P.S. system: In this system, the unit of length is foot, of mass is pound, and time is second.
(3) M.K.S. system: In this system, the unit of length is metre, of mass is kilogram and of time is second.

Definition

Metric Prefix