Introduction to Measurements

A measurement is the act of finding the size or amount of a physical quantity, which requires both a number and a standard unit to be stated clearly. Anything that can be measured, such as the length of an object or the speed of a vehicle, is called a physical quantity.

The problem with body measurements

In the past, people measured length from one end of an object to the other using the size of their hands, called a cubit (mulam). Because hand sizes differ from person to person, this method was unreliable. If a spy and a blacksmith measured a box using their own cubits, an iron container made by the blacksmith would not fit properly. Modern measuring tapes solved this problem by providing fixed numbers that are standard worldwide.

Types of physical quantities

• A fundamental quantity is a basic measurement that stands on its own, such as length.
• A derived quantity is calculated using fundamental quantities, such as speed, which is found by dividing distance by time.
• Every measurement must include both a number and a unit, such as stating a car journey as 5 kilometers, to be clearly understood.

Multiples and sub-multiples of units

• Adding 1 centimeter 100 times makes 1 meter.
• Adding 1 meter 100 times makes 1 hectometer, and adding it 1000 times makes 1 kilometer, which are multiples of units.
• Dividing 1 centimeter into 10 smaller equal parts creates millimeters, which are sub-multiples of units.
• Measuring an object horizontally gives its length, while measuring it vertically gives its height.

Standard SI units

To prevent confusion caused by different systems, the International System of Units, known as SI units, established standard units across the world:

• Length is measured in meters, mass in kilograms, and time in seconds.
• Temperature is measured in Kelvin.
• Electric current is measured in amperes.
• Luminous intensity is measured in candelas, and amount of substance is measured in moles.