The metre-kilogram-second

The unit of force, known as the Newton, is that force which will give an acceleration of 1 m/s to a mass of one kilogram. Thus 1 N = 1 kg m/s with dimensions MLT , and one Newton equals 10 dynes. The energy unit, the Newton-metre, is 10 ergs and is called the Joule and the power unit, equal to one Joule per second, is known as the Watt. 

Unit 1 Newton (1 N) Unit 1 Joule (1 J) Unit 1 Watt (1 W) 

For many purposes, the chosen unit in the SI system will be either too large or too small for practical purposes, and the following prefixes are adopted as standard. Multiples or sub-multiples in powers of 10 are preferred and thus, for example, millimetre should always be used in preference to centimetre. 

These prefixes should be used with great care and be written immediately adjacent to the unit to be qualified furthermore only one prefix should be used at a time to precede a given unit. Thus, for example, 10 metre, which is one millimetre, is written 1 mm. 10 kg is written as 1 Mg, not as 1 kkg. This shows immediately that the name kilogram is an unsuitable one for the basic unit of mass and a new name may well be given to it in the future. 

Some special terms are acceptable, and commonly used in the SI system and, for example, a mass of 10 kg (1 Mg) is called a tonne (t) and a pressure of 100 kN/m is called a bar. 

---

It is usual these days to express all physical quantities in the system of units referred to as the Systeme International, SI for short. The International Unions of Pure and Applied Physics, and of Pure and Applied Chemistry both recommend SI units. The units are based on the metre, kilogram, second and the ampere as the fundamental units of length, mass, time and electric current. (There are three other fundamental units in SI, the kelvin, mole and candela which are the units of thermodynamic temperature, amount of substance and luminous intensity, respectively.)... 

The metre-kilogram-second (mks system and the Systeme International d Unites (SI)... 

When describing a measurement, you normally state both a number and a unit (e.g. the length is 1.85 metres ). The number expresses the ratio of the measured quantity to a fixed standard, while the unit identifies that standard measure or dimension. Clearly, a single unified system of units is essential for efficient communication of such data within the scientific community. The Systeme International d Unites (SI) is the internationally ratified form of the metre-kilogram-second system of measurement and represents the accepted scientific convention for measurements of physical quantities. 

The problem with the SI base unit being a kilogram is the kilo part. The philosophical idea behind the SI system says any parameter (physical, chemical, mechanical, etc.) can be derived from a suitable combination of the others. For example, the SI unit of velocity is metres per second (m s-1), which is made up of the two SI fundamental units of length (the metre) and time (the second). A few of these combinations are cited in Table 1.3. 

According to the modern convention, measurable quantities are expressed in SI (System Internationale) units and replace the centimetre-gram-second (cgs) system. In this system, the unit of length is a metre (m, the unit of mass is kilogram (kg) and the unit of time is second (s). All the other units are derived from these fundamental units. The unit of thermal energy, calorie, is replaced by joule (1 J = 107 erg) to rationalize the definition of thermal energy. Thus, Planck s constant... 

To communicate effectively, scientists rely on a standard system of measurement. As you have learned in previous studies, this system is called the International System of Units (Le systeme international d unites, SI). It allows scientists anywhere in the world to describe matter in the same quantitative language. There are seven base SI units, and many more units that are derived from them. The metre (m), the kilogram (kg), and the second (s) are three of the base SI units. You will learn about two more base units, the mole (mol) and the kelvin (K), later in this book. 

Units of pressure In this book, pressure has been measured in units of mmHg. This is the unit most commonly encountered in acid-base physiology but, in respiratory physiology, there is a move to change to the use of kilopascals, abbreviated kPa. A pascal is one newton per square metre one newton is the force which, when applied to a mass of one kilogram, produces an acceleration of one metre per second per second. The conversion between mmHg and kPa is ... 

Here p is the density of the manometer liquid g, the earth s gravitational acceleration and Ah, the difference of height of the two columns of liquid. If mercury at a temperature of 0 °C is used and Ah is measured in millimetre, pressure values can be stated in Torr (mm Hg). Inserting p, g and Ah in the Sl-units kilogram, metre and second the result is given in the Sl-pressure unit Pa. 

In the International System of Units (SI), there is a basic unit for each physical quantity. The basic unit of length is the metre, the basic unit of time is the second, the basic unit of mass is the kilogram and the basic unit for the amount of a substance is the mole. Other units can be derived from these. 

An absolute system has several advantages, the greatest being simplicity of calculations. A force of a newton accelerates a mass of one kilogram one metre per second squared. In contrast, a force of one kilogram accelerates the same mass 9.80665 metres per second squared. 

For historic reasons a number of different units of measurement have evolved to express quantity of the same thing. In the 1960s, many international scientific bodies recommended the standardisation of names and symbols and the adoption universally of a coherent set of units—the SI units (Systeme Internationale d Unites)— based on the definition of five basic units metre (m) kilogram (kg) second (s) ampere (A) mole (mol) and candela (cd). 

The second parameter in the isotherm is the capacity the amount that will be adsorbed when the solute concentration becomes high. Then the surface will be (almost) completely covered with solute. The surface occupied by a solute molecule is usually in the range of 10 to 10 m . If you know both this value and the interface area of the adsorbent you can calculate the capacity of the adsorbent. This can be given in many units in kilograms or moles per cubic metre, or per kilogram of adsorbent, or in other ways. 

It is important to be conversant with the relations, which convert these atomic units of quantum theory into the modem SI [Systeme International] or mks set of units (37) with length measured in metres, m, mass in kilograms, kg, while time is measured in seconds and energy is measured in joules, J, with... 

The basic SI units of mass, length and time are the kilogram (kg), metre (m) and second (s). The basic unit of thermodynamic temperature is the kelvin (K), but temperatures and temperature differences may also be expressed in degrees Celsius (°C). The unit for the amount of substance is the mole (mol), defined as the amount of substance which contains as many elementary units as there are atoms in 0.012 kg of carbon-12. Chemical engineers, however, are tending to use the kilomole (kmol = 10 mol) as the preferred unit. The unit of electric current is the ampere (A). 

SI Units International System of Units was established in 1973-74 to develop a uniform method of reporting results worldwide. The basic units are metre (m), kilogram (kg), second (s), ampere (A), Kelvin (K), mole (mol) and candela (cd). Acceptable units outside the SI system are litre (1), grams per litre (g/1), moles per litre (M), day (d), hour (h) and minute (min). 

Systeme International d Unites Known more commonly as SI units, it is a system comprising sevenbase units of the international metric system. The units are metre (m) for length, kilogram (kg) for mass, ampere (A) for electrical current, second (s) for time, kelvin (K) for temperature, candela (cd) for luminosity, and mole (mol). Derived units are the newton, joule, pascal, and watt. 

---