Introduction To measure physical quantities, we need standard units. Imagine if everyone measured length differently! That’s why we use a System of Units to maintain consistency in science and engineering. What is a Unit? A unit is a standard measure used to express a physical quantity. For example: Length → meter (m) Mass → kilogram (kg) Time → second (s) The International System of Units (SI Units) The SI system is the modern form of the metric system. It includes seven base units: Quantity Unit Symbol Length Meter m Mass Kilogram kg Time Second s Electric Current Ampere A Temperature Kelvin K Amount of Substance Mole mol Luminous Intensity Candela cd Advantages of SI Units Universal and consistent. Decimal-based, easy to convert. Used in education, research, and industry. Other Systems (for reference only) CGS System: Uses centimeter, gram, second. FPS System: Uses foot, pound, second. (Still used in the U.S.) Conclusion Using a standar...