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The concept of size is something which we all acquire pretty early in our lives. As children, we have an idea about what is big and what is small, mostly in comparison to us. However, there is one important aspect to this which we realise later on, and that is the relative nature of what we call size. Size of objects or of any entity for that matter has no meaning in itself. Size is just an approximation of one entity as compared to another.

To understand this, let us look at a cat first from our perspective and then from a new perspective. If we see a cat, we perceive it as a small animal, but now if we look at a cat through the eyes of a beetle, the cat will appear huge. This ambiguity is because size is relative.

The measurement of objects or other entities can be done in several ways. Size can mean the length, width or height of a body, i.e., its dimensions. Size can also mean the mass or weight of a body. Size can also be the volume or the amount of space a body occupies. Before we determine the size of objects, we need to know what we want to measure. Essentially for physical understanding, three quantities constitute the measurement of objects. These are:

The Three Dimensions: This means the height, length and width of the object. These are the objects measured in metres.

Mass: This is a measure of how heavy the body is. These are generally the objects measured in grams.

Volume: This is a measure of how much space a body occupies. These are generally the objects measured in cubic centimetres.

As we have seen, the size of the objects is purely relative. When we say size, we talk about magnitude in comparison to another, and this comparison leads to quantitative analysis. The size of clothing, footwear and even portion sizes is an example of this, and the understanding of this is important for daily life activities. Since size truly matters both in the world of science as well as in the wild, a lot of effort has been put into the systematic study of this concept.

The outcome of this study is the scales of measurement we have, which we use to determine the measurement of objects scientifically.

We have several scales for object measurement, raging from ancient to modern and belonging to different regions. Each of these scales has its unit system. A unit is a known standard with which we compare our given quantity to acquire a magnitude. Therefore all measurements have a magnitude and unit. Two of the most used system of units across the globe are:

The International System of Units or S.I. system.

The C.G.S. system of units.

The SI system is a standard unit system which is a modern form of the much-used metric system. It has a defined set of units for the basic or primary physical quantities and defines the length in metres, weight in kilograms, time in seconds and so on. The SI system allows for an infinite number of other units known as derived quantities which come from manipulating the primary units. This system of units is prevalent in most of the places across the world other than the U.S.A. and surrounding areas. The SI system gives us a universally recognised scale for the measurement of objects.

The C.G.S. system of units is another supplant of the metric system and uses three basic quantities, namely centimetres for length, grams for weight and seconds for time. All other quantities are derivatives of these base units. Although the S.I. system is the most widespread system of units that we use, there are many areas which require the implementation of the C.G.S. system. In many parts of physics, for instance, C.G.S. is heavily used to elaborate on some theories. Therefore, the C.G.S. system is another way to convey the size of objects and other measurable entities.

Q1. Explain the process of measuring a straight line using a ruler and determining its length.

Ans: If we have to measure the length of a straight line drawn on paper, we need a common centimetre or metre scale or to determine the same. The process of measurement is as follows:

Take the ruler and align the 0 marks with one end of the straight line.

Make sure the edge of the ruler is completely aligned with the line.

Look from a perpendicular angle at the mark which coincides with the other end of the straight line.

Note the value of this mark. This point marks the magnitude of the length. The unit of the scale used for measurement is also equally important and must find mention.

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FAQ (Frequently Asked Questions)

Q1. Why do we Say that Size of Objects is Relative?

Ans: Size, in general, is something which has no meaning. Size is the description of a body when compared to another. A body by itself has no size until and unless we compare it to some known standard. For example, a bar of chocolate cannot be big unless you are aware of a bar which is smaller compared to the first one. When compared to a butterfly, a squirrel is quite big, but for a human, the squirrel is tiny. These are the comparisons which lead to the concept of size, and without these comparisons, the idea of the size of objects or the measurement of objects is meaningless. Hence, size is relative.

Q2. In How Many Ways can we Determine the Size of Objects?

Ans: When we say size, we are mostly talking of matter. Since matter is everything that has a shape and occupies some space, size is the measure of these properties of matter. A physical entity can have a length in one, two or three dimensions, namely height, width and length. It can have a certain mass, and it can occupy some space as in volume. Therefore, size deals with these quantities, wherein length and mass are basic, and volume is a derived quantity. You use a ruler to measure dimensions and a protractor to measure angles. When you have similar objects, the ratios of their dimensions when comparing one object to the other will be the same for all the dimensions.