SYSTEMS OF MESURMENT

Index Cover ……………………………………………………………..1 Index ………………………………………………………………2 What is a “system of measurment”…………………3 History of measurment……………………………………4 Us custumary system……………………………………….5 Units of cuerrency……………………………………………6 Conversion Tables……………………………………………7

A system of measurement is a set of units which can be used to specify anything which can be measured and were historically important, regulated and defined because of trade and internal commerce. Scientifically, when later analyzed, some quantities are designated as fundamental units meaning all other needed units can be derived from them, whereas in the early and most historic eras, the units were given by fiat (see statutory law) by the ruling entities and were not necessarily well inter-related or self- consistent.

History of measurment Although we might suggest that the Egyptians had discovered the art of measurement, it is only with the Greeks that the science of measurement begins to appear. The Greek's knowledge of geometry, and their early experimentation with weights and measures, soon began to place their measurement system on a more scientific basis. By comparison, Roman science, which came later, was not as advanced... The French Revolution gave rise to the metric system, and this has spread around the world, replacing most customary units of measure. In most systems, length distance), weight and time are fundamental quantities; or as has been now accepted as better in science, the substitution ofmass for weight, as a better more basic parameter. Some systems have changed to recognize the improved relationship, notably the 1824 legal changes to the imperia system. Later science developments showed that either electric charge or electric current must be added to complete the minimum set of fundamental quantities by which all other metrical unis may be defined. Other quantities, such as power speed etc. are derived from the fundamental set; for example, speed is distance per unit time. Historically a wide range of units was used for the same quantity, in several cultural settings, length was measured in inches feet yards fathoms rods, chains, furlongs, miles, nautical miles, stadia, leagues, with conversion factors which were not simple powers of ten or even simple fractions within a given customary system. Nor were they necessarily the same units (or equal units) between different members of similar cultural backgrounds. It must be understood by the modern reader that historically, measurement systems were perfectly adequate within their own cultural milieu, and the understanding that a better more universal system (based on more rationale and fundamental units) only gradually spread with the maturation and appreciation of the rigor characteristic of Newtonian physics. Moreover, changing a measurement system has real fiscal and cultural costs as well as the advantages that accrue from replacing one measuris g system with a better one. Once the analysis tools within that field were appreciated and came into widespread use in the emerging sciences, especially in the applied sciences like civil and mechanical engineering, pressure built up for conversion to a common basis of measurement. As people increasingly appreciated these needs and the difficulties f converting between numerous national customary systems became more widely recognised there was an obvious justification for an international effort to standardise measurements. The French Revolutionaryspirit took the first significant and radical step down that road. In antiquity, systems of measurement were defined locally, the different units were defined independently according to the length of a king's thumb or the size of his foot, the length of stride, the length of arm or per custom like the weight of water in a keg of specific size, perhaps itself defined in hands and knuckles. The unifying characteristic is that there was some definition based on some standard, however egocentric or amusing it may now seem viewed with eyes used to modern precision. Eventually cubitsand stridasgave way under need and demand from merchants and evolved to customary units. In the metric system and other recent systems, a single basic unit is used for each fundamental quantity. Often secondary units (multiples and submultiples) are used which convert to the basic units by multiplying by powers of ten, i.e., by simply moving the decimal point Thus the basic metric unit of length is the metre a distance of m is millimetres, or kilometres. Current practice

Us custumary sistem ==Natural units== [[Natural units]] are [[Physics|physical]] [[units of measurement]] defined in terms of universal [[physical constants]] in such a manner that some chosen physical constants take on the numerical value of one when expressed in terms of a particular set of natural units. Natural units are natural because the origin of their definition comes only from properties of [[nature]] and not from any human construct. Various systems of natural units are possible. Below are listed some examples. * [[Geometrized unit system Geometric unit systems]] are useful in [[Theory of relativity|relativistic physics]]. In these systems the base physical units are chosen so that the [[speed of light]] and the [[gravitational constant]] are set equal to unity. * [[Planck units]] are a form of geometric units obtained by also setting [[Boltzmann's constant]], the [[Coulomb's law Coulomb force constant]] and the [[reduced Planck constant]] to unity. They might be considered unique in that they are based only on properties of [[free space]] rather than any prototype, object or particle. * [[Natural units#Stoney units|Stoney units]] are similar to Planck units but set the [[elementary charge]] to unity and allow Planck's constant to float. * [[Natural units#"Schrödinger" units|"Schrödinger" units]] are also similar to Planck units and set the elementary charge to unity too but allow the speed of light to float. * [[Atomic units]] (au) are a convenient system of units of measurement used in [[atomic physics]], particularly for describing the properties of [[electron]]s. The atomic units have been chosen such that the fundamental electron properties are all equal to one atomic unit. They are similar to "Schrödinger" units but set the [[electron mass]] to unity and allow the gravitational constant to float. The unit [[energy]] in this system is the total energy of the [[electron]] in the [[Bohr atom]] and called the [[Hartree energy]]. The unit length is the [[Bohr radius]]. * [[Natural units#Electronic system of units|Electronic units]] are similar to Stoney units but set the [[electron mass]] to unity and allow the gravitational constant to float. They are also similar to Atomic units but set the speed of light to unity and allow Planck's constant to float. * [[Natural units Quantum electrodynamical system of units Quantum electrodynamical units]] are similar to the electronic system of units except that the [[proton mass]] is normalised rather than the electron mass.

Units of cuerrency

Conversion tables Imperial Metric 1 inch [in]2.54 cm 1 foot [ft]12 in m 1 yard [yd]3 ft m 1 mile1760 yd km 1 int nautical mile yd1.853 km