Category Science

WHAT WAS THE EARLIEST SYSTEM OF MEASUREMENT?

It is likely that the first systems of measurement were based on the human body. As every person had a body, they could use themselves as reference! Of course, since people vary greatly in size, this was not a very accurate system.

This article looks at the problems surrounding systems of measurement which grew up over many centuries, and looks at the introduction of the metric system. Is the meaning of measurement? It is associating numbers with physical quantities and so the earliest forms of measurement constitute the first steps towards mathematics. Once the step of associating numbers with physical objects has been made, it becomes possible to compare the objects by comparing the associated numbers. This leads to the development of methods of working with numbers.

The earliest weights seem to have been based on the objects being weighed, for example seeds and beans. Ancient measurement of length was based on the human body, for example the length of a foot, the length of a stride, the span of a hand, and the breadth of a thumb. There were unbelievably many different measurement systems developed in early times, most of them only being used in a small locality. One which gained a certain universal nature was that of the Egyptian cubit developed around 3000 BC. Based on the human body, it was taken to be the length of an arm from the elbow to the extended fingertips. Since different people have different lengths of arm, the Egyptians developed a standard royal cubit which was preserved in the form of a black granite rod against which everyone could standardise their own measuring rods.

To measure smaller lengths required subdivisions of the royal cubit. Although we might think there is an inescapable logic in dividing it in a systematic manner, this ignores the way that measuring grew up with people measuring shorter lengths using other parts of the human body. The digit was the smallest basic unit, being the breadth of a finger. There were 28 digits in a cubit, 4 digits in a palm, 5 digits in a hand, 3 palms (so 12 digits) in a small span, 14 digits (or a half cubit) in a large span, 24 digits in a small cubit, and several other similar measurements. Now one might want measures smaller than a digit, and for this the Egyptians used measures composed of unit fractions.

It is not surprising that the earliest mathematics which comes down to us is concerned with problems about weights and measures for this indeed must have been one of the earliest reasons to develop the subject. Egyptian papyri, for example, contain methods for solving equations which arise from problems about weights and measures.

A later civilisation whose weights and measures had a wide influence was that of the Babylonians around 1700 BC. Their basic unit of length was, like the Egyptians, the cubit. The Babylonian cubit (530 mm), however, was very slightly longer than the Egyptian cubit (524 mm). The Babylonian cubit was divided into 30 kus which is interesting since the kus must have been about a finger’s breadth but the fraction 1/30 is one which is also closely connected to the Babylonian base 60 number system. A Babylonian foot was 2/3 of a Babylonian cubit.

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WHAT ARE SI UNITS?

SI units are internationally agreed units for scientific measurements. SI stands for a French phrase: Systeme Internationale d’ Unites (International System of Units). The base units are those used for the basic measurements that can be made, while derived units are those that need to be worked out using one or more base units. For example, a newton is the force needed to accelerate a mass of one kilogram by one metre per second.

The International System of Units (SI, abbreviated from the French Système international (d’unités)) is the modern form of the metric system. It is the only system of measurement with an official status in nearly every country in the world. It comprises a coherent system of units of measurement starting with seven base units, which are the second (the unit of time with the symbol s), metre (length, m), kilogram (mass, kg), ampere (electric current, A), kelvin (thermodynamic temperature, K), mole (amount of substance, mol), and candela (luminous intensity, cd). The system allows for an unlimited number of additional units, called derived units, which can always be represented as products of powers of the base units. Twenty-two derived units have been provided with special names and symbols. The seven base units and the 22 derived units with special names and symbols may be used in combination to express other derived units, which are adopted to facilitate measurement of diverse quantities. The SI system also provides twenty prefixes to the unit names and unit symbols that may be used when specifying power-of-ten (i.e. decimal) multiples and sub-multiples of SI units. The SI is intended to be an evolving system; units and prefixes are created and unit definitions are modified through international agreement as the technology of measurement progresses and the precision of measurements improves.

Since 2019, the magnitudes of all SI units have been defined by declaring exact numerical values for seven defining constants when expressed in terms of their SI units. These defining constants are the speed of light in vacuum, c, and the hyperfine transition frequency of caesium, the Planck constant h, the elementary charge e, the Boltzmann constant k, the Avogadro constant NA, and the luminous efficacy kcd. The nature of the defining constants ranges from fundamental constants of nature such as c to the purely technical constant. Prior to 2019, h, e, k, and NA were not defined a priori but were rather very precisely measured quantities. In 2019, their values were fixed by definition to their best estimates at the time, ensuring continuity with previous definitions of the base units. One consequence of the redefinition of the SI is that the distinction between the base units and derived units is in principle not needed, since any unit can be constructed directly from the seven defining constants.

The current way of defining the SI system is a result of a decades-long move towards increasingly abstract and idealised formulation in which the realisations of the units are separated conceptually from the definitions. A consequence is that as science and technologies develop, new and superior realisations may be introduced without the need to redefine the unit. One problem with artefacts is that they can be lost, damaged, or changed; another is that they introduce uncertainties that cannot be reduced by advancements in science and technology. The last artefact used by the SI was the International Prototype of the Kilogram, a cylinder of platinum-iridium.

The original motivation for the development of the SI was the diversity of units that had sprung up within the centimetre-gram-second (CGS) systems (specifically the inconsistency between the systems of electrostatic units and electromagnetic units) and the lack of coordination between the various disciplines that used them. The General Conference on Weights and Measures (French: Conférence générale des poids et mesures – CGPM), which was established by the Metre Convention of 1875, brought together many international organisations to establish the definitions and standards of a new system and to standardise the rules for writing and presenting measurements. The system was published in 1960 as a result of an initiative that began in 1948. It is based on the metre-kilogram-second system of units (MKS) rather than any variant of the CGS.

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WHY DO WE NEED ACCURATE MEASUREMENT?

For many purposes, an approximate idea of a length or weight or distance is fine. We may say that something is five minutes’ walk away, for example. That does not tell us how far it is — that would depend on how quickly a person walked — but it does give a rough idea that it is neither hundreds of kilometres nor just a few centimetres distant. However, if you need to know whether a new car would fit in your garage, you need a more accurate measurement, at least within a few centimetres. An Olympic high jumper, in fierce competition, will certainly need to measure to the nearest centimetre. And so it goes on, until scientists measuring the size of atoms need units of measurement much too small to be seen with the naked eye. The important thing is that units of measurement must be standard (agreed by everyone who uses them).

Accurate measurements are important because precise amounts are required for reactions to take place, for a recipe to turn out and to keep correct records of a measurement. When measurements are not accurate, this provides incorrect data that can lead to wrong or even dangerous conclusions or results.

When measuring, measurements that are not accurate provide data that is wrong. If something is based off an object or individual’s weight, having an inaccurate weight is dangerous. For example, a prescription drug that has a weight-based dosage could have a dosage that is too low to treat a condition. If a lab experiment calls for a specific amount of a chemical, measuring the wrong amount may result in an unsafe or unexpected outcome.

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WHAT IS A HOMOLOGOUS SERIES?

A homologous series is a group of compounds that are made of the same elements and share some of the same properties and features but have different numbers of atoms in their molecules. Alkanes, alkenes and alcohols all form homologous series.

Homologous series is a series of compounds with similar chemical properties and same functional group differing from the successive member by CH2. Carbon chains of varying length have been observed in organic compounds having the same general formula. Such organic compounds that vary from one another by a repeating unit and have the same general formula form a series of compounds. Alkanes with general formula CnH2n+2, alkenes with general formula CnH2n and alkynes with general formula CnH2n-2 form the most basic homologous series in organic chemistry.

The successive members vary from each other by a CH2 unit. For example in CH4 and C2H6, the difference is -CH2 unit and the difference between C2H6 and C3H8   is also -CH2 unit. So CH4, C2H6, and C3H8 are homologs. The same thing can be observed in case of alkenes in which the first member is ethene and the successive members are C3H6, C4H8, and C5H10. They differ from each other by a –CH2 unit. Alkene formula is written as CnH2n.

All the members belonging to this series have the same functional groups. They have similar physical properties that follow a fixed gradation with increasing mass. The properties of CH3OH, C2H5OH, and C3H7OH are similar and follow a gradual change with increasing molecular mass of the successive members of the series. This is because, with the increase in the molecular mass of the compounds, the number of bonds also increases. Therefore, properties such as melting and boiling point, solubility, etc. that depend on the mass and the total number of bonds in a compound show a gradual change with an increase in molecular masses of the compounds. Chemical properties of the members of a homologous series are the same due to the fact that they all have the same functional groups in them.

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WHAT ARE CARBOXYLIC ACIDS?

Carboxylic acids contain carbon, oxygen and hydrogen. Many naturally occurring acids are carboxylic acids, such as the acid that causes nettles to “sting” and the acid in vinegar. This is called thionic acid. It is created when alcohol reacts with oxygen (oxidizes).

Carboxylic acids with low molecular weights dissolve in water because the carboxyl group forms several hydrogen bonds with water. A carboxylic acid acts both as a hydrogen bond donor through its hydroxyl hydrogen atom and as a hydrogen bond acceptor through the lone pair electrons of both oxygen atoms. The solubility of carboxylic acids, like that of alcohols, decreases with increasing chain length because long nonpolar hydrocarbon chains dominate the physical properties of the acid.

Carboxylic acids dissolve in common alcohol solvents such as ethanol. This solubility results from intermolecular hydrogen bonds between solute and solvent, and from van der Waals attractions between the ethyl group of ethanol and the nonpolar tail of the carboxylic acid. Nonpolar solvents, such as chloroform, are also excellent solvents for carboxylic acids. In these solvents, the carboxylic acids exist as relatively nonpolar hydrogen-bonded dimers that are compatible with the solvent.

Carboxylic acids are characterized by the strong absorption due to the carbonyl group in the infrared spectra of these compounds. The absorption occurs in the same region as the carbonyl groups of aldehydes and ketones, but the absorption for carboxylic acids occurs at slightly higher wavenumber, and tends to be somewhat broadened. The O—H bond of carboxylic acids absorbs in the same region as that for alcohols. However, the absorption is very much broader for carboxylic acids, and it overlaps the C—H absorptions.

Some carboxylic acids are found in fats and oils from animals and plants. They are called fatty acids. When they react with alcohol, they create compounds called esters, which give flowers their scent. Some expensive perfumes are still made by distilling the scent from flowers and preserving it in alcohol.

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WHAT IS THE CARBON CYCLE?

Carbon is an essential element in all living things. It is constantly being recycled on Earth in the carbon cycle.

Carbon is the foundation of all life on Earth, required to form complex molecules like proteins and DNA. This element is also found in our atmosphere in the form of carbon dioxide (CO2). Carbon helps to regulate the Earth’s temperature, makes all life possible, is a key ingredient in the food that sustains us, and provides a major source of the energy to fuel our global economy.

The carbon cycle describes the process in which carbon atoms continually travel from the atmosphere to the Earth and then back into the atmosphere. Since our planet and its atmosphere form a closed environment, the amount of carbon in this system does not change. Where the carbon is located — in the atmosphere or on Earth — is constantly in flux.

On Earth, most carbon is stored in rocks and sediments, while the rest is located in the ocean, atmosphere, and in living organisms. These are the reservoirs, or sinks, through which carbon cycles. Carbon is released back into the atmosphere when organisms die, volcanoes erupt, fires blaze, fossil fuels are burned, and through a variety of other mechanisms.

In the case of the ocean, carbon is continually exchanged between the ocean’s surface waters and the atmosphere, or is stored for long periods of time in the ocean depths. Humans play a major role in the carbon cycle through activities such as the burning of fossil fuels or land development. As a result, the amount of carbon dioxide in the atmosphere is rapidly rising; it is already considerably greater than at any time in the last 800,000 years.

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