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| Measurements |
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| Everything that we use in our daily life
is ultimately governed by principles of physics. All gadgets we use everyday
at home, bicycles and cars, all different types of machinery and
instruments, work on principles of physics. Hence to understand even the
elementary working of these things, the study of physics is essential. |
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| For understanding the relationships
between matter and energy, measuring them is very essential. There are
thousands and thousands of different things around us. There are different
kinds of forces around us and there are different kinds of energies that we
come across every day. Thus there would be millions and millions of physical
quantities and energies that could be measured. Yet you would be surprised to
know that there are only six basic units from which all other units are
derived. These basic units are the units of length, mass, time, electric
current, temperature and luminous intensity. Out of these only three
fundamental or basic units of measurements are used in mechanics. |
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| These are the units length, mass and time. All the measurements in physics are related to these three fundamental units. All other units of measurements can be derived from these three fundamental units. |
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| While discussing these units of
measurement we must be clear about two terms - unit and measure number. For
example, when we say that the length of a line is five centimeters, the unit
we have chosen is centimeter and the measure number is five as the line is
five times the unit length. |
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| Most experiments in physics require the observations made to be quantitative rather than qualitative. If observations are only descriptive or qualitative, they are likely to be imprecise and could cause disagreements between experimenters. For example, scientists cannot merely say that an object is large or small. Instead they have to specify its size as a quantity, that is, with a number and using a standard unit such as kilogram. This is called a quantitative observation. |
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| As science advanced through the centuries, the importance of accurate and uniform measurements was
realized
all over the world. In order to enable scientists working in different parts
of the world to compare their measurements, a need for certain basic unit of
measurement was felt and hence later a basic unit was defined. |
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| Unit is a standard for comparison. In earlier times the measurement of quantity of things was quite arbitrary. In many cases it was related to the dimension of different parts of the human body. These parts were chosen as "units" to measure these quantities. For example, for measuring length, distance between the nose and the fingers or outstretched hand was used as a unit. Can you imagine the confusion caused when different countries used different units or measures! This also caused a lot of inconvenience. |
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| In this system the unit of length is foot (F), of mass is the pound (P) and of time is the second (S). |
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| Metric Units in Common Use and their Relationship |
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| At last in 1789 a system of measurement was invented based upon the powers of ten. Each unit quantity was divided into ten parts and each of these parts into further ten and so on. Multiples of the unit are ten, one hundred, one thousand etc. This was very logical. Once the size of the unit had been determined say, the "meter", submultiples were named
decimeter, centimeter, millimeter for one tenth, one hundredth and one thousandth of a
meter respectively. Multiples were named as the decameter (x 10), hectometer (x 100) and
kilometer (x 1000) etc. |
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| The prefixes used in the system are shown in table below: |
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| The above system is called the Metric
system, which literally means, "measuring system". In the Metric System
there are two commonly used systems of measurement, one based on the Meter,
Kilogram and Second (MKS) and the other on the Centimeter, Gram and Second (CGS). |
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