measurement

MEASUREMENTS
“When you can measure what you are talking about and express it in numbers you know something about it, but when you cannot, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the stage of a science, whatever the matter be.” This is the saying of Lord Kelvin. In physics, all the measurable quantities are referred to as physical quantities. These quantities characterize physical properties of matter. Length, mass, time, speed, temperature, displacement etc are few examples of physical quantities.
The physical quantities which are independent of other physical quantities are known as basic or fundamental quantities. All then other physical quantities derived with help of these basic quantities are known as derived quantities. Any standard chosen unit demands the following physical characteristics as it should be accessible, invariable and easily reproducible.