Units and Measurement -Homi Bhabha Jr. Scientist 6th

What is measurement in science?

Table of Contents

There are some common questions we hear in daily life.

1.How old are you?

2.How hot is today?

3.How much do you weigh?

4.How tall are you?

5.How much water can be filled in your bottle?

To answer the above questions we need to measure different quantities.

To find how old you are, you need to measure time.

To find out how hot it is today, you need to measure the temperature.

To know how much you weigh, you must weigh yourself to find mass of your body.

To know how tall you are, you need to measure your height (length)

To know how much water you can fill in your water bottle, you need to measure the capacity of your bottle.

If you want to measure length of a pencil ,you take a ruler and match the end points of the pencil with the markings on the ruler. The length of the pencil is an unknown quantity and the distances on the ruler are know quantities.

So, to measure the length of the pencil ,you compared unknown quantity with a known quantity and that is measurement.

Measurement-Measurement means comparison of an unknown quantity with some known fixed quantity of the same kind.

Measurement is the process of determining the magnitude of a physical quantity such as length , time, mass, temperature etc.

Measurement consist of two parts.

Magnitude
Unit of measurement

e.g. Length of pencil is 8 cm

8-The numerical part 8 is magnitude

cm- is the unit

8 cm- is the measurement

Units Of Measurement And Types Of Units

Unit:- Whenever we measure an unknown physical quantity we do so by comparing it with some known quantity. This known quantity is called unit of measurement.

Units are of two types.–

1. Non-standard units

2.Standard units

Non-standard or traditional units/ Ancient units –In ancient times people used their body parts for measurement. These units were not precise and differ from person to person. They are called non-standard units or ancient units or traditional units.

They are :

Hand span– Distance between tip of thumb and tip of last finger
Cubit– Distance between tip of middle finger and elbow
Arm length– Distance between tip of middle finger and shoulder
Foot step or a pace- Length of foot
Pace- distance covered in one pace
Yard– Distance from stretched arm to the chin.
Width of four fingers
Fistful-Amount of grains, a fist can hold

Standard units-The units which are acceptable all over the world as basic units of measurement are called as standard units.

Need of standard units–

To measure quantities accurately.
To convey these measurements to other people in such a way that they understands us or for the sake of uniformity.

Characteristics of standard unit-

It should be of convenient and measurable size.
It should be reproducible.
It should be unchangeable.
It should not be perishable.
It should not change with time.
It should not change with physical conditions like pressure temperature etc.

Requirements of choosing right unit:-

The choice of unit is based on certain requirements.

The unit should be capable of being precisely defined so that there is no confusion.
The unit should be easily reproducible so that copies can be easily created in other laboratories for reference purposes.
The unit should be independent of the time and place of measurement

Rules Of Writing The Names and Symbols Of Units Of Measurement :-

There are some rules for the use of names and symbols denoting units.

Units are named after the name of the scientist who proposed it or after the name of the instrument.

Symbols of units which are named after the name of scientist are to be denoted by capital letters and other with small letters. e.g. N(newton-Unit of Force), K(kelvin-Unit of Temperature), W(watt-Unit of Power),J(joule-Unit of energy/work),A(ampere-Unit of current).
The full name of a unit always begins with small letters such as kelvin, newton, second.
The symbols are never plural. They are written in singular form. Names of the units can be written in plural form. e.g.- 5 meters or 5m and not 5 ms.
Unit is not to be followed by full stop.

Standard Units Of Measurement

Standard Units- The units which are acceptable all over the world as basic units of measurement are called as standard units.

Need of standard units–

1.To measure quantities accurately.
2.To convey these measurements to other people in such a way that they understands us or for the sake of uniformity.

Characteristics of a standard unit-

It should be of convenient and measurable size.
It should be reproducible.
It should be unchangeable.
It should not change with time.
It should not be perishable.
it should not change with physical conditions like pressure temperature etc.St

Systems of Units Of Measurement

A system of units-A system which defines the fundamental units ,in comparison with which a fundamental quantity can be expressed is referred to as system of units.

Different systems of units have been developed over a period of time.

The following systems of units are in common use.

M.K.S. system – meter-kilogram-second
C.G.S. system – centimeter- gram-second
F.P.S. system – foot-pound-second

1.M.K.S. system-In this system the units of length, mass and time are meter, kilogram and second respectively.

Giovanni Giorgi was an Italian physicist. He was the first one to introduce the M.K.S system. He introduced M.K.S. Sysrem in 1901.

2.C.G.S. system- In this system the units of length, mass and time are centimeter- gram-second respectively.

The CGS system was invented in 1832 by the German mathematician Carl Friedrich Gauss

3.F.P.S. system-The foot pound second system or FPS system is a system of units built on the three fundamental units foot for length, pound for either mass and second for time.In this system the units of length, mass and time are foot-pound-second respectively.

Everett proposed FPs system in 1861.

S.I. systems of units-

The scientists all over the world accepted a basic set of units for the measurement of physical quantities.

This system or set of units is called’Systeme Internationale de unites( in French) and in short SI system of units.

This system was adopted in 1960.But the current version of S.I. was completed in1971 by adding the mole as a base unit for amount of substance.

The unit of time is same in all three systems. i.e. second

Multiples And Submultiples Of Units Of Measurement-

Multiples–

To create larger forms of the units factors that are used are called multiples of units.
Multiples of units are used for larger measurements.

Submultiples–

The factors which help in getting smaller forms of the units are called submultiples of the units.Submultiples of units are used for smaller measurements.

Multiples

Submultiples

Prefix name

Prefix symbol

Multiplying factor

Prefix name

Prefix symbol

Multiplying factor

Deca

Hecto

Kilo

Mega

Giga

Tera

Peta

Exa

Meria

10¹

10²

10³

10⁶

10⁹

10¹²

10¹⁵

10¹⁸

10⁴

Deci

Centi

Milli

Micro

Nano

Pico

Femto

Atto

10^-1

10^-2

10^-3

10^-6

10^-9

10^-12

10^-15

10^-18

Conclusion

Measurement means comparison of an unknown quantity with some known fixed quantity of the same kind.

Measurement is the process of determining the magnitude of a physical quantity such as length , time, mass.
Whenever we measure an unknown physical quantity we do so by comparing it with some known quantity. This known quantity is called unit of measurement.
In ancient times people used their body parts for measurement. These units were not precise and differ from person to person. They are called non-standard units or ancient units or traditional units.
Handspan, Cubit, Armlength, Footstep,Yard, Pace, Feastful are Examples of Ancient/Traditional Units.
The units which are acceptable all over the world as basic units of measurement are called as standard units.
The scientists all over the world accepted a basic set of units for the measurement of physical quantities. This system or set of units is called’Systeme Internationale de unites( in French) and in short SI system of units.
Multiples Of Units Of Measurement-To create larger forms of the units factors that are used are called multiples of units.Multiples of units are used for larger measurements.
Submultiples-The factors which help in getting smaller forms of the units are called submultiples of the units.Submultiples of units are used for smaller measurements.
This blog is useful for the students who are preparing for Homi Bhabha Jr. Scientist Exam. Or Sir C.V. Raman Science Talent Hunt Exam.