Time

Time  is defined by its measurement: time is what a clock reads.[1] In classical, non-relativistic physics, it is a scalar quantity (often denoted by the symbol {\displaystyle t}t) and, like length, mass, and charge, is usually described as a fundamental quantity. Time can be combined mathematically with other physical quantities to derive other concepts such as motion, kinetic energy and time-dependent fields. 

The duration between any two events is called time. The SI unit of time is second.

Measurement of Time

For the measurement of time, a clock is used. There are different types of clocks like the mechanical clock, wristwatch, pendulum clock, quartz clock, etc. Time is measured in different ways. It can be measured in second, minute, hour, day, week, month, year etc. Second is the smallest unit of time. For the short time period, we use second, minute and hour and for log time period, we use day, week, month and year. For the measurement of the very long time period, we use decade, century, millennium, etc. The multiples and sub- multiples of a second are given below,

60 seconds = 1 minute
60 minutes = 1 hour
24 hours = 1 day
7 days = 1 week
365 days = 1 year
10 years = 1 decade
100 years = 1 century
1000 years = 1 millennium

Regular and irregular objects

Various types of substances are found in our surrounding. They have different shape and sizes. Some substances have fixed geometrical shape and some do not have. Those substances that have fixed geometrical shapes are called regular objects. Some of the examples of regular objects are books, pencils, chalk box, basketball, etc.
Those substances which do not have a fixed geometrical shape are called irregular objects. Some of the examples of irregular objects are the pieces of broken glass, a piece of stone, a broken piece of brick, leaf, etc.

Area

The total space occupied by the plane surface of the object is known as the area of that object. The SI unit of area is the square metre (m2). Other similar units of area are mm2, cm2, km2, etc.

Measurement of Area of Regular Plane Surfaces

There are various formulae used for the measurement of the area of the regularplane surface. Some of them are given below,

• Area of a rectangular object (A) = length(l) ×× breadth(b)
  ∴ A= l ×× b
• Area of a circle (A)=π ×× (radius)2[ π = 227227 ]
  ∴ A=πr2
• Area of a square (A)= (length)2
  ∴ A= l2

Example 1
The radius of the circle is 7cm, if the value ofπ is 227227, then what is the area of circle.

Solution:
Given,
Radius (r)= 7 cm
π = 227227
Area (A)= ?
By using formula,
A =πr2
=227227 ×× 72
= 22 ×× 7
= 154cm2

Measurement of Area of Irregular Surfaces

There are no exact formulae for the measurement of the area of irregular surfaces. But we can measure the area of irregular surfaces by using graph paper. A graph paper is divided into equal- sized squares of side 1 cm and 1 mm.
At first, the irregular object is placed on the graph paper. Then the outline of the object is drawn on the graph paper. After this, the number of squares covered by the outline is counted. The number of squares that are more than half is also counted but the squares less than half are not counted. Then by adding two numbers, the area of the given irregular object is calculated.

Volume

The total space occupied by the body is called volume. In SI system, the unit of volume is a cubic meter (m3). Other similar units are mm3, cm3, ml, l, etc. The volume of solid is measured in mm3, cm3, m3, etc. Measuring cylinders are used for the measurement of the volume of liquids. The volume of liquids is measured in ml, l, etc,

1 ml = 1cm3 or 1cc (cubic centimetre)
1000 ml = 1l (litre)
1000 cm3 = 1l

Measurement of Volume of Regular Solids

For the calculation of the volume of regular solids, various formula is used which are given below,

• Volume of a cuboid (V)= length(l) ×× breadth (b) ×× height(h)
  ∴ V= l ×× b ×× h ××
   
• Volume of a cube (V)= (length)3
  ∴ V= l3
• Volume of sphere (V)= 4343π(radius)3
  ∴ V=4343πr3
• Volume of cylinder (V)=π ×× (radius)2 ×× height (h)
  ∴ V=πr2h

Example 2

The length, breadth and height of the cuboid is 3cm, 6cm and 9cm respectively. Calculate the volume of cuboid.

Solutions:
Given,
Length(l)= 3cm
Breadth(b)= 6cm
Height(h)= 9cm

According to the formula, we have

∴ V= l ×× b ×× h ××
= 3 ×× 6 ×× 9
= 162cm3

Measuring the Volume of Liquids

The volume of the liquids are measured by using differnt measuring cylinders such as graduated cylinder, milkman's measure, pipette, burette, milkman's measure. etc. It is measured in millilitre(ml) or cubic centimetre (cc) and litre(l). Litre is mostly used.
At first for the measurement of the volume of liquids, the liquid is poured into the measuring cylinder, then the volume of the liquid is calculated by observing the reading given on the surface of the cylinder.
There are various types of liquids. While measuring the volume of liquids, some liquids form a concave surface on the cylinder and some form convex surface in the cylinder. Liquids like oil, water, alcohol, etc form a concave surface and liquids like mercury, etc form a convex surface in the cylinder. For the liquid forming convex surface, the reading should be taken from the upper meniscus and for the liquid forming concave mirror, the reading should be taken from the lower meniscus.

Measuring the Volume of Irregular Solids

We can measure the area of irregular bodies by using graph paper. But it is impossible to measure the volume of irregular bodies by using graph paper. We can measure the volume of irregular bodies by using measuring cylinder. This method is based on the fact that the volume of an irregular solid is equal to the volume of water displaced by it when it is immersed in water. When we immerse an irregular body in water, it displaces some amount of water. The volume of displaced water is equal to the volume of an irregular body that displace water. This method can be used to calculate the volume of those irregular bodies which sink in water and do not dissolve in water.

Experiment 1
Object: To measure the volume of a piece of stone.
Materials Required: Measuring cylinder, water, thread, a piece of brick

Procedure

Af first, fill the measuring cylinder partially with water. Note down the level of the water. Let it be the initial level of water, V1. While recording the level of water, keep the eye in the level with the bottom of the meniscus to avoid parallax error. After this, tie the piece of stone with the help of thread and immerse it into the water of measuring cylinder. We can see that, the level of water rises. Then, note down the new level of water carefully. Let it be the final reading, V2.

Observation

Suppose V1 is 50 ml and V2 is 75 ml.
Now,
Initial volume of water in the cylinder (V1)= 50 ml
Final volume of water in the cylinder (V2)= 75 ml
∴ Volume of the water displaced (V)=V2 -V1
= 75ml - 50ml
= 25ml

∴ Volume of the Stone= Volume of water displaced
= 25ml

Precautions

• While taking the readings, the water should be at rest and the measuring cylinder should be placed on a horizontal surface .
• For the liquid forming convex surface, the reading should be taken from the upper meniscus and for the liquid forming concave mirror, the reading should be taken from the lower meniscus.