Measurement

Measurement is defined as the comparison between unknown quantities with known quantities of the same kind. To approach the subject quantitatively, it is essential that we make measurements.

A physical quantity is that which can be measured directly or indirectly. Mass, length, time, density, etc. are some examples of the physical quantity.

The measurement of unknown quantity can be done by comparing it with a standard quantity of the same kind. Thus, the comparison of an unknown quantity with a known quantity with a known or standard quantity is called measurement.

Importance of Measurement

• Measurement is essential in selling and buying goods.
• It is essential in performing scientific experiments to establish the truth about a physical phenomenon.
• It is required for the global understanding of the quantity of a substance.
• It is essential in performing the experiment for making our daily food.
• Measurement of the medicine is a must in the treatment of diseases.

Fundamental quantity and derived quantity

Those physical quantities, which can neither be derived from others nor be further resolved into simpler quantities, are called fundamental quantities. Length, mass, and time are the fundamental quantity. And the units of fundamental quantities are called fundamental units or basic units.

For example length of the body is a fundamental quantity as it cannot be expressed in terms of other quantity.

Those physical quantities, which depend on two or more fundamental quantities or power of a fundamental quantity, are called derived quantities. And the units of derived quantities are called derived units.

For example, Area is a derived quantity. Since area= l × b, so it depends on the power of length.

Unit

The reference standard with which we carry out the measurement of any physical quantity of the same kind is called unit. For example, the meter is the unit of length and kg is the unit of mass.

Standard system of units

In Nepal, some people still use the local units like haat and mana for measurement of length and mass. These units may vary from place to place. So, in order to maintain the uniformity in measurement of physical quantities, the following standard units are used:

• MKS system: In this system, mass, time, and length are measured in a kilogram, second and meter respectively. It is also known as the metric system.
• CGS system: In this system, length is measured in centimeter, mass in gram and time in second.
• FPS system: In this system, length, mass, and time are measured in foot, pound and second respectively.
• SI system: It is the most important system of units. It is also the improved version of the MKS system. Simply put, a system of physical based on the meter, kilogram, second, ampere, kelvin, candela, and mole, together with a set of prefixes to indicate multiplication or division by a power of ten is known as the SI system. It can be divided into two groups; fundamental unit and derived unit.

Fundamental quantities and their units

Advantages of International System over other System of Units

• The International system is the rational system of units. That is, this system makes use of only one unit for physical quantity.
• It is a coherent system of units. That is, in this system, all the derived units can be easily obtained from fundamental units.
• It is a metric system that multiplies and sub-multiplies can be expressed as powers of 10.