# Chapter 1 Physical Quantities and Measurements

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The name “Physical Quantities Measurement” refers to a group of quantities that can be measured together. A physical quantity, or physical variable, is a quantity (such as time, temperature, or mass) that can be measured and whose value describes a biological system. These quantities are usually represented by a symbol, such as t for time or m for mass.

The measurement of a physical quantity is often called a number, which can be expressed in terms of the base quantity via a concrete measurement procedure.

A physical quantity is independent of the choice of a measurement unit and is not affected by changes in the system it describes.

In physics, the dimensions of physical quantities represent how they are mathematically related to other portions. For example, speed and velocity both describe motion; however, the rate has dimensions of distance/time, whereas speed does not.

Physical quantities are characterized by magnitude, dimension, and units.

Magnitude is the size or value of a physical quantity. Magnitude is expressed as a number with a dimension.

Dimension is the property of a physical quantity that determines how it affects other physical quantities. A set of dimensions (for example, length, mass, and time) that describe all the properties of a material amount are called fundamental dimensions.

Unit is the standard measure of any given physical quantity defined by an international convention, for example, meters for length and grams for mass.