## Friday, September 5, 2014

### Measuring Physical Quantities with Units

Physics is a branch of sciences which deals with the study of the nature. In this subject measuring the physical quantity is very important. In physics something is meaningful,only when we are able to measure and express it with certain units and dimensions.

Whenever you're talking in terms of physics,we always think of how to measure a physical quantity. Thus measurement has a significant importance while we are studying physics.So to measure physical quantities we use units and to express physical quantities we use dimensional formulas.

We can divide the entire physical quantities broadly into two categories. The physical quantities which are independent of any of the other physical quantities are called as fundamental quantities. Some simple examples of the fundamental quantities are like length mass and time. It is as simple as that time is not going to depend on any other physical quantities.

The physical quantities which are derived basing on the fundamental quantities are called as derived physical quantities. displacement,velocity,acceleration and force are some of the derived physical quantities.

To measure this physical quantities we use units. There are different systems of units to measure physical quantities. If the scale of the measurement in any physical quantity is large, then the corresponding numerical value will be small. For example if you want to measure the length of your body in terms of meters and in terms of centimeters, it's numerical value will be less in terms of meters when compared with centimeters. It is simply because the unit meter is a large unit, the length of the body appears to be small in number.

There are different systems of units in which the physical quantities can be measured. Among them F.P.S system,C.G.S system and M.K.S systems are prominent ones. All these three systems are actually used to measure three fundamental quantities length, Mass and time. In the following table the comparison of the three different kinds of systems is described.

In FPS system,to measure length measures we use the unit foot and to measure mass we use with the unit called Pound. The problem in measuring the length with feet, is not having a sort of consistency. Whenever we are adopting a unit as a standard unit, it shall be universal, easily reproducible, accessible for everybody, and standard so that everybody can follow easily. As feet is being inconsistent and varies from person to person in terms of size, we are no more preferring the unit feet.

In CGS system there is a small issue in measuring the length with the unit called centimeter. This unit is too small to measure long distances. Hence we have introduced another system called MKS system. For many years MKS system is being used as a standard system.

As science has been developed with respect to time it has been notice that there are some other physical quantities which are also independent in nature. By taking them into consideration, a new system called standard international system is designed. This system has length, Mass and the time as the fundamental physical quantities similar to MKS system.

It also has new physical quantities like electric current which is measured with the unit called Ampere, temperature, intensity of light and quantity of matter. There are two more supplementary physical quantities like angle and solid angle. All this physical quantities are together are called as standard international system. Right now we are following this system to measure all the physical quantities that are existing around us.

Rules in writing units:

1. If a unit is measured in the name of scientists and when it is written in full name we shall not start the unit with a capital letter.
2. When you are writing the symbol of a unit in the name of a scientists it has to be represented with a capital letter in a single letter.
3. No punctuation marks Shall be used at the end of the units.
4. Unit shall be always expressed in singular but not in plural.
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