# Units, Dimensions And Measurement

## What is called a Measurement?

Measurement is defined as an activity for defining the specifications or quantification of attributes of an object or event. It actually involves an activity of comparison of an unknown quantity with a known quantity having similar attribute.

After measuring the dimension, we get the results in a numeric value after which a unit is added for complete specification of the attribute.

Thus, measuring of a physical quantity is the process of comparing it with a standard amount of same kind of quantity called its unit.

We can measure the length, mass, capacity (or volume) and temperature of any given object.

EXAMPLE –

Let, we have to measure the size of a pencil.

Size of a pencil has linear attribute called “length”. To measure the length of a pencil or any other similar item, we use measuring instrument called metric scale. A metric scale has graduation marks in meter, centimeter and millimeter.

Here, length of the pencil is the unknown quantity to be measured and graduations marked on the metric scale are the known quantities called units.

Both, pencil and scale are kept side by side for comparing their length attributes as shown in figure (A). The reading observed on the scale graduations tells about the measurement of length of pencil.

Let, the one end of the pencil corresponds to 0 graduation mark and other end corresponds to ‘5.3’ graduation mark of scale as shown in figure.

Then the length of the pencil will be taken as 5.3 centimeters or 5 centimeters and 3 millimeters.

In the figure, figure (A) illustrates direct measuring technique and figure (B) illustrates indirect measuring technique.

## Measuring Systems

Observation or result of measurement of a physical quantity is comprises of two distinct parts (1) first is a number (2) and the second is an unit of measurement. Meaning of measuring system actually implies the system of units used in the measuring activity.

A complete set of units used to measure all kinds of quantities is called a system of units.

Choosing of measuring systems i.e. units for a specific measurement depends upon two factors –

1. The size of measuring object.
2. Accuracy of results.

For smaller objects, it needs smaller units such as millimeter, centimeter etc. and for larger objects, it needs larger units of measurement such as meter, kilometer etc.

Some of most commonly used measuring systems are –

1. CGS System of measurements.
2. FPS System of measurements.
3. MKS System of measurements.
4. SI System of measurements.

### CGS System of Measurement –

CGS system was first set up in France. It uses centimeter, gram and second as the fundamental units of length, mass and time respectively.

### FPS System of Measurement –

FPS system was first set up in Britain. It uses foot, pound and second as the fundamental units of length, mass and time respectively. It is also called as “British System“.

### MKS System of Measurement –

It is a French system based on meter, kilogram and second as the fundamental units of length, mass and time respectively. It is also called as “Metric System“.

### SI System of Measurement –

SI system is the most popular unit system. It is a modified form of MKS system of measurement based on meter, kilogram and second as the fundamental units of length, mass and time respectively. It is also called as “International System of Units“.