Physics : 1. Units and measurements.

Fundamental quantity

A physical quantity which do not depend on any other physical quantity for Its measurement.

Derived quantity

A physical quantity which depend on fundamental quantity for its measurement.

Physical Quantities

Measurable quantities expressed with a number and a unit.

Types of Quantities

Fundamental (independent, e.g., length, mass, time) & Derived (dependent, e.g., velocity, force, pressure).

Unit

Standard reference for measurement of a physical quantity.

SI System

International system of 7 base units (m, kg, s, A, K, cd, mol).

SI Superiority

Universal, coherent, practical, rationalized.

Derived Units Examples

Newton (N), Joule (J), Pascal (Pa), Coulomb (C).

Least Count

Smallest measurable value of an instrument.

Accuracy

Closeness of measurement to the true value.

Precision

Closeness among repeated measurements.

Why no absolute accuracy?

Due to instrument limitations, environment, and human errors.

Error

Difference between measured value and true value.

Absolute Error

|Measured – True|.

Mean Absolute Error

Average of all absolute errors.

Relative Error

(Absolute error / True value).

Percentage Error

(Relative error × 100).

Why prefer % error over absolute error?

It is independent of magnitude, gives relative accuracy.