MEASUREMENT

INTRODUCTION

 If all the countries in the world are ever going to speak one language then that will be promoted by measurement. 

Measurement is the process of calculating the size, rate, effect etc. of something by comparing their quantity to a fixed quantity. 

Quantities which can be measured include length, mass, temperature, time, etc. These are known as physical quantities. 

Knowing the correct measurements of some quantities was a global problem until the introduction and adoption of a new system of units measurement known in French as the Le Systēme International d’Unitēs (International System of Units), abbreviated to SI. SI units are described as standard units.

 A standard unit is a unit that is understood and accepted globally. 

In the S.I system, there are two main units of measurements – the basic and the derived units. 

Basic units

* Basic units of the SI system Basic units are the units from which other units can be obtained. They are also known as the fundamental units. 

In the SI system, there are seven basic units. Each of the basic unit has a symbol and an SI unit in which it is measured.

(Base quantities, their corresponding SI units, and their symbols)

Derived units 

Apart from the base units, there are other units which are derived from the base units. 

These are called the derived units. 

* Derived units are units which are obtained from the base units. 

It is a combination of two or more base units or a base unit and a derived unit.

(Derived quantities and their SI unit)

USING MEASURING INSTRUMENT

Different quantities have different instruments with which they are measured. 

The instruments used to measure length are the metre rule, the surveyor‘s tape, measuring tape, ruler etc. 

The vernier calliper measure short distances, internal and external diameters of hollow objects. It measures to the precision of 0.1 mm. 

The micrometer screw gauge on the other hand is used to measure extremely short distances to the precision of 0.01 mm. It can therefore be used to measure the thickness of paper, cloth, etc. 

The vernier calliper and the micrometer screw gauge are known as the precision instruments.

Thermometers are used to know the temperature of an object. 

Hydrometers measure the densities of liquids. 

Balances are used to measure the mass of an object. Some examples of balances are beam balance, top pan balance, electronic balance. 

The volumes of liquids are measured with measuring cylinder, pipette, burette, volumetric flask, beaker etc.

(Basic measuring instruments) 

                                                                           (Vernier Caliper)

DENSITY

The density of a substance is it mass per unit volume. 

Density is expressed mathematically as: 

Density is measured in kilogram per cubic metre (kg/m3 or kgm-3 ). Remember that the SI unit of mass is kg, and that of volume is m3 . Therefore mass per volume (mass/volume) is kg/m3 . 

Measuring the Density of Liquid 

 Measure the mass of a clean measuring cylinder as M1 

 Pour a known volume of liquid into the measuring cylinder. 

  Record that as V. 

 Measure the mass of both beaker and liquid. Record it as M2. 

Hence: Mass of liquid (M) = Mass of beaker and liquid (M2) – Mass of beaker (M1) 

 i.e. M = M2 – M1 

Volume of liquid = V

Density of regular objects 

A regular object is an object which has uniform dimensions that can be determined with a ruler. 

To find the density of a regular object, example a book, 

 Find its volume by multiplying its length, breadth and height. 

 With the aid of a balance, measure the mass of the book. 

Hence, density =  

Density of Irregular Objects 

Irregular objects are objects which do not have definite dimensions. Examples are stone, fragment of glass or metal, a piece of coal, etc. 

Procedure: 

  Measure and record the mass of the object as M 

 Pour water into a measuring cylinder and record the volume as V1

 

 Tie a string around the irregular object and lower it gently into the measuring cylinder. 

 Record the level of water as V2. Calculation Mass of the object = M Volume of the object = V2 – V1

Density (ρ) of the irregular object = Mass (M) of the object/ Volume (V2 – V1)