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Conversions between units in the metric system are defined by their prefixes (for example, 1 kilogram = 1000 grams, 1 milligram = 0.001 grams) and are thus not listed in this article. Exceptions are made if the unit is commonly known by another name (for example, 1 micron = 10 −6 metre).
For example, 10 miles per hour can be converted to metres per second by using a sequence of conversion factors as shown below: = . Each conversion factor is chosen based on the relationship between one of the original units and one of the desired units (or some intermediary unit), before being rearranged to create a factor that cancels out the ...
The kilogram is defined in terms of three defining constants: [4] a specific atomic transition frequency Δν Cs, which defines the duration of the second, the speed of light c, which when combined with the second, defines the length of the metre, and the Planck constant h, which when combined with the metre and second, defines the mass of the ...
A derived unit is used for expressing any other quantity, and is a product of powers of base units. For example, in the modern metric system, length has the unit metre and time has the unit second, and speed has the derived unit metre per second. [5]: 15 Density, or mass per unit volume, has the unit kilogram per cubic metre. [5]: 434
By contrast, if "==" is used, the unit code is defined as the first unit "per" the second. As well as a ratio of two units, a per unit can be of the form "currency per unit". The module recognizes "$" and "£" as currency symbols and shows them appropriately.
Mass flow rate is defined by the limit [3] [4] ˙ = =, i.e., the flow of mass through a surface per time .. The overdot on ˙ is Newton's notation for a time derivative.Since mass is a scalar quantity, the mass flow rate (the time derivative of mass) is also a scalar quantity.
[4]: 2 For example, using metre per second is coherent in a system that uses metre for length and second for time, but kilometre per hour is not coherent. The principle of coherence was successfully used to define a number of units of measure based on the CGS, including the erg for energy , the dyne for force , the barye for pressure , the ...
Metric units are units based on the metre, gram or second and decimal (power of ten) multiples or sub-multiples of these. According to Schadow and McDonald, [1] metric units, in general, are those units "defined 'in the spirit' of the metric system, that emerged in late 18th century France and was rapidly adopted by scientists and engineers.