A physical quantity is a property of a material or system that can be measured or quantified. Each physical quantity is expressed as the product of a numerical value and a unit of measurement. For example, in "2 meters," 2 is the numerical value and meter is the unit

. Physical quantities are fundamental to science because they allow us to describe, compare, and calculate properties of matter and energy. Examples include mass, length, time, temperature, electric current, luminous intensity, and amount of substance

Components of a Physical Quantity

• Numerical Value: The magnitude or amount (e.g., 5, 10.2).
• Unit: The standard of measurement (e.g., meters, kilograms, seconds).
• (For vectors) Direction: Some physical quantities also have direction, such as velocity or force

Types of Physical Quantities

Physical quantities are classified into two main types:

• Base (Fundamental) Quantities: These are independent and cannot be defined in terms of other physical quantities. According to the International System of Quantities (ISQ), the seven base quantities are:
  • Length (meter, m)
  • Mass (kilogram, kg)
  • Time (second, s)
  • Electric current (ampere, A)
  • Thermodynamic temperature (kelvin, K)
  • Amount of substance (mole, mol)
  • Luminous intensity (candela, cd)

• Derived Quantities: These are defined in terms of base quantities through mathematical relationships. Examples include:
  • Velocity (meters per second, m/s)
  • Acceleration (meters per second squared, m/s²)
  • Force (newton, N)
  • Pressure (pascal, Pa)
  • Volume (cubic meter, m³)

Scalar, Vector, and Tensor Quantities

• Scalar: Has only magnitude (e.g., mass, temperature).
• Vector: Has both magnitude and direction (e.g., velocity, force)

• Tensor: More complex, can have magnitude, direction, and orientation (e.g., stress tensor)

Summary Table

Type| Examples| Description
---|---|---
Base (Fundamental)| Length, Mass, Time, Temperature, etc.| Cannot be defined in terms of other quantities
Derived| Area, Volume, Velocity, Force, Pressure, etc.| Defined using base quantities
Scalar| Mass, Temperature, Energy| Magnitude only
Vector| Velocity, Force, Displacement| Magnitude and direction

In summary, physical quantities are measurable properties that describe the physical world, always expressed as a numerical value multiplied by a unit, and are foundational to all scientific measurement and analysis