There are 3 types of physical quantities based on standardisation, base, derived quantities, and supplementary quantities. However, before scientists agreed on this universal system of measurement, different systems were used in different parts of the world.
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Introduction
The Metric System was introduced in the late 1700s in France and became popular in the 1800s. Two key metric systems were the CGS system (centimetre-gram-second) and the MKS system (meter-kilogram-second).
The CGS system was widely used in science, especially in physics, while the MKS system came later and eventually led to the modern SI system.
At the same time, when CGS system was active in France, the Imperial System was in use in the British Empire, and later on the US Customary System came on the screen which was a variant of the Imperial System, and was used in the United States.
These systems relied on different units for length, weight, and volume, which often created confusion, especially when scientists from different countries tried to compare their findings.
In 1960, the International System of Units (SI) was created to solve these issues. This new system, based on the MKS system and soon became a standardised measurement tool across the globe, making it easier for scientists to work together and share results.
Physical Quantity
A physical quantity is a characteristic or property of an object or phenomenon that can be measured and expressed numerically.
Types of Physical Quantities
Based on standardisation, physical quantities are categorized into three main types.
Base Quantities
They are defined as, “fundamental quantities that cannot be defined in terms of other quantities.”
They form the foundation of the measurement system. According to international system of units (SI system), these quantities are only 7.
Examples
- Length: Measured in meters (m).
- Mass: Measured in kilograms (kg).
- Time: Measured in seconds (s).
- Temperature: Measured in kelvins (K).
- Electric Current: Measured in ampere (A).
- Speed of Light: Measured in candela (cd).
- Amount of Substance: Measured in moles (mol)
Derived Quantities
They are defined as, “quantities obtained by combining base quantities using mathematical operations (+, –, ×, ÷).”
They describe more complex aspects of physical phenomena. There are numerous quantities of such types as per SI system.
Examples
- Speed: Defined as distance divided by time (meters per second, m/s).
- Acceleration: Defined as speed divided by time (squared meter per second, m2/s)
- Force: Defined as mass multiplied by acceleration (newtons, N).
Supplementary Quantities
They are defined as, “additional quantities used to describe specific properties that are not covered by base or derived quantities.”
They help provide a complete description of certain physical phenomena.
Examples
There only two supplementary quantities in SI.
Plane Angle
A plane angle is a measure of the rotation or inclination between two intersecting lines or rays in a flat (two-dimensional) plane. It is defined as:
“The ratio of the length of the arc formed by the angle to the radius of the circle.”
It is measured in radians (rad) in the SI system.
Solid Angle
A solid angle is a measure of the three-dimensional angle formed at the apex of a cone that subtends a surface area on a sphere. It is analogous to the plane angle but applies in three dimensions. The solid angle is defined as:
“The area of the spherical surface subtended by the cone, divided by the square of the radius of the sphere.”
In the SI, its unit is steradian (sr).
Conclusion
Understanding the distinction between base, derived, and supplementary quantities is essential for making accurate and standardised measurements in science.
The first one (base) serve as the foundation, while the second (derived) expand on them to describe more complex phenomena. Supplementary quantities fill in gaps, allowing for precise measurement in areas like angles.
Together, these 3 types of physical quantities ensure consistency and clarity in scientific research and everyday applications, making it easier to communicate results and foster collaboration across the globe.
By adopting a universal system like the SI, scientists have simplified and unified the way we measure the world around us.
Frequently Asked Questions (FAQs)
What are physical quantities?
These are measurable characteristics or properties of an object or phenomenon, such as length, mass, time, or temperature, expressed numerically.
What are the 3 types of physical quantities?
The three types are base, derived, and supplementary quantities.
What are base quantities?
These quantities are fundamental measurements that cannot be defined by other quantities, like length (meter), mass (kilogram), and time (second).
How many base quantities are there in the SI system?
There are seven of these quantities in the SI system: length, mass, time, temperature, electric current, amount of substance, and luminous intensity.
What are derived quantities?
These quantities are obtained by combining base quantities using mathematical operations. Examples include speed (meters per second), force (newtons), and acceleration (meters per second squared).
Can you give an example of a derived quantity?
An example is speed, which is defined as distance divided by time, measured in meters per second (m/s).
What are supplementary quantities?
These quantities describe specific aspects that are not covered by base or derived quantities, such as angles. Examples include plane angle (radians) and solid angle (steradians).
What is the difference between the CGS and MKS systems?
The CGS system uses centimeters, grams, and seconds for measurements, while the MKS system uses meters, kilograms, and seconds. The MKS system is the basis for the modern SI system.
Why was the SI system introduced?
The SI system was introduced to create a universal and standardised system of measurement, making it easier for scientists worldwide to communicate and compare results.
What are the units for plane angle and solid angle in the SI system?
Plane Angle
In the SI, the unit of plane angle is the radian (rad).
One radian is defined as, “the angle subtended by an arc whose length is equal to the radius of the circle.”
Solid Angle
The unit of solid angle in SI is the steradian (sr).
One steradian is defined as, “the angle subtended by a surface area equal to the square of the radius on the surface of a sphere.”