There are several reasons.
Measurement units evolved over time. People used different units across countries over time. Even now, you have the Imperial system that has been mostly abandoned by developed countries across the world. But USA, Burma, Liberia and a few Caribbean islands still use the Imperial system (or a variant).
Differences in scale: It would make little sense to measure the distance between two cities in metres, or the size of an ant. In the first case you would use a kilometre, in the second a millimetre.
Sometimes the way in which a physical measure is derived will affect its units. Energy can be defined as the ability to do work and so the unit is the same as the unit for work: a Joule. However, thermal energy is defined as the amount of heat required to raise the temperature of 1 gram of pure water by 1 kelvin and in 1 calorie.
A unit conversion ratio
It could be the definition of equivalent ratios.
What is a fraction in which the numerator and denominator represent the same amount but are in different units?
No. The same quantities in different units.
In mathematics, two quantities are said to be in units agreement if they have the same units of measure. For example, if two quantities are both measured in meters, then they are in units agreement. If one quantity is measured in meters and the other is measured in centimeters, then they are not in units agreement.
Multiple units may be associated with the same physical quantity due to historical reasons (different regions developing their own units) or different systems of measurement (metric vs imperial). In some cases, units may be related by simple conversion factors, allowing for flexibility in expressing measurements.
The amount or size of physical quantity depends on two things " number and unit". Every physical quantity has its own standard for fixed amount which is called as unit. The same physical quantity with larger or smaller size is measured in different units. for example 1cm or 1m Therefore even if we have to measure same physical quantity with larger or smaller size of it we should have a standard for comparison.
treu
No. "Dimensionless" means there are NO units involved.
False. Units can be converted between different physical quantities as long as the conversion factor relates the two quantities. For example, you can convert between meters and kilometers, even though they represent different lengths.
A unit conversion ratio
Weight is a measure of the gravitational force acting on an object due to its mass. It is typically measured in units such as pounds or kilograms.
There are a few reasons. Historical and cultural: different units were used at in different parts of the world at different times. Many of these "traditional" units were eventually replaced by the SI system. However, even within the SI system, there are different units which are appropriate at different orders of magnitude. For example, the metre is the standard unit for length but it is not the most sensible unit for atomic distances, nor is it appropriate for distances between cities. Furthermore, in astronomy or cosmology there are other units such as an astronomical unit (AU = average distance between the earth and sun), a light year (the distance travelled by light, through vacuum, in one year), a parsec (the distance at which a star appears to be displace by one second of arc between the two extreme positions in the earth's orbit).
It could be the definition of equivalent ratios.
The physical quantity that is the same for waves belonging to different electromagnetic spectrum is the speed of light. The speed of light in a vacuum is constant and is approximately 3.00 x 10^8 meters per second.
work and energy have same unit which is jole denoted by "J"
First the units of the two quantities should have the same category, e.g length units, or mass units, etc. Second: to convert the unit of one quantity to the same unit of the another quantity. third: to perform the comparison.