Physical Quantities

In our daily life, we measure many things, like the weight of fruits, the temperature of the body, or the speed of vehicles. These measurements, such as mass, weight, distance, speed, temperature, and volume, are called physical quantities. Every physical quantity has two parts: a value and a unit. For example, if Swarali walks two kilometres every day, "two" is the value and "kilometres" is the unit of distance.

1. Fundamental Quantities: These are basic quantities like length, mass, and time. They are not derived from any other quantities.

2. Derived Quantities: These quantities are formed from fundamental quantities. For example, speed is derived from distance and time (speed = distance ÷ time).

3. Scalar Quantities: A scalar quantity can be described completely with just a value and a unit without any direction.

Examples include:

• Length (e.g., 2 meters)
• Temperature (e.g., 37°C)
• Mass (e.g., 50 kilograms) These quantities don't need direction to be understood.

4. Vector Quantities: A vector quantity is one that requires both a value and a direction to be completely described.

Examples include:

• Displacement (e.g., 20 kilometers north)
• Velocity (e.g., 500 km/h towards Mumbai): These quantities need both magnitude and direction to be meaningful.

A quantity that can be measured by an instrument and through which we describe the laws of the physical world is called a physical quantity.

The basic physical quantities that cannot be derived from other quantities and serve as the foundation for all measurements is called fundamental quantities.

The quantities that are derived from fundamental quantities through mathematical relationships is called derived quantities.

A value, quantity, or magnitude in terms of which other values, quantities, or magnitudes are expressed is called a unit.

A set of particular physical quantities from which different other units can be obtained, which are neither derived from one another nor resolved into any other units is called fundamental units.

Units that are derived from fundamental units — such as force, which is mass × acceleration — and are expressed algebraically using base units is called derived units.

Units that are neither fundamental nor derived but are accepted in the SI system (e.g., radian for plane angle, steradian for solid angle) is called supplementary units.

The smallest value up to which an instrument can measure is called the least count.

Least count = \[\frac {\text {Smallest reading on main scale}}{\text {No. of divisions on main scale}}\]

Instrument Least Count = \[\frac {\text {Main scale least count}}{\text {Divisions on secondary scale}}\]