The generally accepted reference for measuring physical quantities (like length, mass, time, etc.) is the metric system, or in the modern adaptation, is the International System of Units (SI abbreviated from the French Système international (d'unités)).
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here is a need for measurement in physical quantity. Without it , how can you define things.
By measuring a physical quantity we define the properties of a material which the physical quantity is associated with.
Physical quantities are the substances which can be measured. By measuring physical quantities, we can measure the mass, weight and other physical properties
For example, distance, speed, mass, pressure, force, momentum, energy. UNIT: A certain basic, arbitrarily chosen, internationally accepted reference standard used for measurement of a physical quantity is called a unit. For example, metre is a unit of length, second is a unit of time.