Measurement

 

A value and a unit are used to express and measure the magnitude of a physical quantity.

            For example Suresh walks 2 kilometre every day. In this example ‘2’ is the value and ‘kilometre’ is the unit used to express the magnitude of distance which is a physical quantity.

 

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1.     Fundamental and derived quantities:

Generally, physical quantities are classified into two types, namely,

(i)            Fundamental quantities

(ii)         Derived quantities.

 

Fundamental quantities:

            A set of physical quantities which cannot be expressed in terms of any other quantities are known as “Fundamental quantities”. Their corresponding units are called “Fundamental units”.

There are seven fundamental physical quantities in SI Units (System of International Units).

 

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Derived quantities:

                        All other physical quantities which can be obtained by multiplying, dividing or by mathematically combining the fundamental quantities are known as “derived quantities”.

Their corresponding units are called “Derived units”.

 

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Area:

            The area is a measure of how much space there is on a flat surface.

            The area of the plot of land is derived by multiplying the length and breadth

                                              Area = length × breadth

            The unit of the area is = meter × meter

                                                         = metre2

                                                         = m2 (Read as square meter).

            Area is a derived quantity as we obtain are by multiplying twice of the fundamental physical quantity length.

            One square meter is the area enclosed inside a square of side 1 meter.

Area of regularly shaped figures

 

            The area of regularly shaped figures can be calculated using the relevant formulae.

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Area of irregularly shaped figures

 

5.PNG                In our daily life, we encounter many irregularly shaped figures like leaves, maps, stickers of stars or flowers, peacock feather etc. The area of such irregularly shaped figures cannot be calculated using any formula.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Volume

            The amount of space occupied by a three dimensional object is known as its volume.

                                    Volume = surface area × height

            The SI unit of volume is cubic meter or m3.

 

Volume of regularly shaped objects

            As in the case of area, the volume of the regularly shaped objects can also be determined using an appropriate formula.

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Volume of liquids

            Liquids also occupy some space and hence they also have volume. But, liquids do not possess any definite shape. So, the volume of a liquid cannot be determined as in the case of solids. When a liquid is poured into a container, it takes the shape and volume of the container. The volume of any liquid is equal to the space that it fills and it can be measured using a measuring cylinder or measuring beaker. The maximum volume of liquid that a container can hold is known as the “capacity of the container”. A measuring container is graduated.

 

 

 

 

            The volume of a liquid is equal to the volume of space it fills in the container. This can be directly observed from the readings marked in the measuring containers.

 

            Liter is the commonly used unit to measure the volume of liquids. We can understand that the unit of volume is cubic cm if the dimensions of the object are given in cm. This cubic cm is commonly known as cc. A volume of 1000 cc is termed as one liter (l).

                                                                        1 liter = 1000 cc or cm3

                                                                        1000 ml = 1 liter

 

To measure the volume of liquids, some other units are also used. Some of them are gallon, ounce, and quart.

 

1 gallon = 3785 ml

1 ounce = 30 ml

1 quart = 1 liter

 

Volume of irregularly shaped objects

            There are no formulae to determine the volume of irregularly shaped objects. For such cases, their volume can be determined using a measuring cylinder and water.

 

Density

            Density of a substance is defined as the mass of the substance contained in unit volume (1 m3).

            If the mass of a substance is “M” whose volume is “V”, then, the equation for density is given as

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            SI unit of density is kg/m3. The CGS unit of density is g/cm3.

Density of different materials

            Different materials have different densities. The materials with higher density are called “denser” and the materials with lower density are called “rarer”.

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Relationship between Mass, Volume and Density

 

Density = Mass/ Volume

Mass = Density × Volume

Volume = Mass / Density

 

 

 

 

 

 

 

 

 

 

 


Measuring distance of celestial bodies

            Normally, we use centimeter, meter and kilo meter to express the distances that we measure in our day to day life. But, for space research, astronomers need to measure very long distances such as the distance between the earth and a star or the distance between two stars. To express these distances, we shall learn about two such units, namely,

i.    Astronomical unit

ii.   Light year

 

Astronomical Unit

 

            One astronomical unit is defined as the average distance between the earth and the sun.

                                    1 AU = 149.6 million km = 149.6 × 106 km = 1.496 × 1011 m.

 

Light Year

            One light year is defined as the distance travelled by light in vacuum during the period of one year.

                                                            1 Light year = 9.46 × 1015 m.

 

 

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