We should note that traditionally the metric system includes the units for mass, distance, and time, while SI is an extended system that includes more basic units, as we discuss below. The metric system evolved into the International System of Units, or the SI, and the two terms are often used interchangeably. The unit for distance, a meter, was linked to the wavelength of light emitted by an atom of krypton-86, but later was redefined as the distance that light travels in a vacuum within a specified timeframe. To address this problem the second was later redefined as a specific number of cycles of radiation emitted during a change of state of an atom of caesium-133. However, it was impossible to verify this constant through experimentation in all of the years that followed 1900, since it was not possible to measure this year once it finished. For example, the unit for time, a second, was defined first as a specific fraction of the tropical year 1900. The metric system went through an evolution and its dependence on artifacts changed to dependence on natural phenomena and constants present in nature. Originally, units of the metric system were based on the artifacts for length and weight, just like in the earlier measuring systems. Many scientists believe that base ten is arbitrary and that we use it only because we have ten fingers, and that if we had a different number of fingers, our numeral system would have been different. The convenience of using a base 10 system is that our most commonly used numeral system is also base ten, therefore it is easy to convert between smaller and larger units. That is, a larger unit divided into ten smaller units, and these smaller units each divided into ten even smaller units, and so on.Īs we can see, not all of the early measuring systems were base 10. It was a base-ten system, meaning that smaller units taken to the power of ten made up larger units. This new system was the decimal metric system. It was not until the French Revolution and subsequent colonization of various regions of the world by France and other European nations that adopted this new system, that the new measuring system was developed and adopted across the globe. Lack of standardization caused similar problems with the units for volume as with those for mass and length.Īs early as the 13th century, and possibly even earlier, scientists and philosophers discussed creating a unified measuring system. For example, the volume of a container, like a jug or a cauldron, would be determined by the number of small items of relatively uniform size, for example, seeds, that fit into the container. Initially, volume was also measured using these small items. Since neither the value of the units nor the number of units that they were divided into were universal, there were confusions and disagreements when merchants from different regions traded with each other. The value of these units varied from region to region, and each larger unit was often comprised of 60, 100, or another number of the smaller units. These larger units often had artifacts, which were standardized weights, generally made of stone. Different regions often used these smaller units such as seeds, and the larger units which were often multiples of the smaller units. It was originally based on the weight of a carob seed. A classic example of this is the unit of mass still in use, the carat, now used for measuring precious stones. Weights, on the other hand, were based on the mass of an individual seed, grain, bean, or another similar object.
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