In physics, a physical quantity is anything that can be measured, such as length, time, or speed.

What are Fundamental Quantities?

Fundamental quantities are the basic building blocks of measurement. They are independent, meaning they do not depend on any other physical quantities for their definition. Scientists have agreed on seven base quantities that cover all measurements in the universe.

• Length: Measured in meters (m).
• Mass: Measured in kilograms (kg).
• Time: Measured in seconds (s).
• Electric Current: Measured in amperes (A).
• Temperature: Measured in kelvin (K).
• Amount of Substance: Measured in moles (mol).
• Luminous Intensity: Measured in candela (cd).

If you measure the height of a desk, you are using the fundamental quantity of length. These values are fixed and serve as the foundation for all scientific calculations.

Understanding Derived Quantities

Derived quantities are physical quantities that are created by combining two or more fundamental quantities. You cannot measure these directly with a single standard unit. Instead, you calculate them using mathematical formulas.

For example, speed is a derived quantity. To find speed, you must divide distance (a fundamental length) by time (a fundamental time). The formula is:

Speed = Distance / Time

Because speed relies on length and time, it is 'derived' from those basic values.

Examples and Differences

Think of fundamental quantities like the letters of the alphabet. You use letters to build words. In physics, fundamental quantities are the letters, and derived quantities are the words.

Another common derived quantity is Area. If you want to find the area of a square, you multiply length by length. Since length is a fundamental quantity, area is derived. Similarly, Force is a derived quantity because it is calculated using mass, length, and time.

Key differences to remember:

• Fundamental quantities are independent; derived quantities depend on others.
• Fundamental quantities have their own base units; derived quantities have units made by combining base units (like m/s for speed).
• There are only seven fundamental quantities, but there are thousands of possible derived quantities.