System of Units

 

A system of units is a collection of units in which certain units are chosen as fundamental and all others are derived from them. This system is also called an absolute system of units. In most systems, the mass, length, and time are considered to be fundamental quantities, and their units are called fundamental units. The following are some systems of units which are in common use.

·         c.g.s. system of units: The unit of length is centimetre (cm). The unit of mass is gram (g). The unit of time is second (s)

·         m.k.s. system of units: The unit of length is the metre (m). The unit of mass is the kilogram (kg). The unit of time is second (s)

·         f.p.s. system of units: The unit of length is a foot (ft). The unit of mass is a pound (Lb). The unit of time is second (s). This system is no more in use. This system is also known as Imperial system or the British Imperial system. Temperature is measured in Fahrenheit.

 S.I. System of Units:

In the year 1960, the Eleventh General Conference of Weights and Measures introduced the International System of Units. The International Standard Organization (ISO) and the International Electrochemical Commission endorsed the system in 1962.  In October 1971 a replacement of the metric system of units was done with a new system called Systeme Internationale d’ Unites. The International System of Units, commonly known as the SI system, is the modern form of the metric system and is the most widely used system of measurement in the world. It provides a standard and coherent set of units for expressing physical quantities.

Fundamental Units:

	Fundamental Quantity	S.I. Unit	Symbol
1	Length	Metre	m
2	Mass	Kilogram	kg
3	Time	Second	s
4	Temperature	Kelvin	K
5	Electric current	Ampere	A
6	Luminous intensity	Candela	cd
7	Amount of substance	mple	mol

Besides these seven basic units, there are two supplementary units. S.I. unit for the plane angle is radian (rad) and that of solid angle is steradian (sd).

Supplementary Units:

	Quantity	S.I. Unit	Symbol
1	Plane angle	radian	rad
2	Solid angle	steradian	sr

This system of units is an improvement and extension of the traditional metric system. Now, this system of units has replaced all other systems of units in all branches of science, engineering, industry, and technology.

Guidelines for Writing SI Units and Their Symbols:

·         All units and their symbols should be written in small case letters e.g. centimetres (cm), metre (m), kilogram per metre cube ( kg m^-3).

·         The units named after scientists are not written with a capital initial letter but its symbol is written in capital letter. Thus the unit of force is written as ‘newton’ or’ N’ and not as ‘Newton’. Similarly unit of work and energy is joule (J), S.I. unit of electric current is ampere (A). The S.I. nit of pressure is pascal (Pa) and that of temperature is kelvin (K).

·         No full stop should be placed after the symbol.

·         The denominators in a compound unit should be written with negative powers. Thus an index notation should be used to write a derived unit. for example unit of velocity should be written as ms^-1 instead of m/s. The unit of density is kilogram per metre cube ( kg m^-3 and not kg/m³)

·         No plural form of a unit or its symbol should be used. example 5 newtons should be written as 5 N and not as 5 Ns.

·         A compound unit obtained from units of two or more physical quantities is written either by putting a dot or leaving a space between symbols of two units. Example unit of torque is newton metre is written as Nm ot N.m. Unit of impulse is newton second is written as N s or N.s.

·         Some space should be maintained between the number and its unit

Advantages of S.I. System of Units:

·         Units are simple to express

·         This system uses only one unit for one physical quantity. Hence it is a rational system of units.

·         Units of many physical quantities are related to each other through simple and elementary relationships   For example 1 ampere = 1 volt / 1 ohm.

·         It is a metric system of units. There is a decimal relationship between the units of the same quantity and hence it is possible to express any small or large quantity as a power of 10. i.e. inter-conversion is very easy.    For e.g. 1kg   =  1000 gm  = 10³ gm

·         The physical quantities can be expressed in terms of suitable prefixes.

·         a joule is a unit of all forms of energy and it is a unit of work. Hence it forms a link between mechanical and electrical units. Hence S.I. the system is a rational system because it uses only one unit for one physical quantity.

·         This system forms a logical and interconnected framework for all measurements in science, technology, and commerce.

·         All derived units can be obtained by dividing and multiplying the basic and supplementary units and no numerical factors are introduced as in another system of units. Hence S.I. system of units is a coherent system. Hence S.I. system of units is used worldwide.

General Steps to Find Derived Unit:

·         Step -1 Write the formula for the quantity whose unit is to be derived.

·         Step -2 Substitute units of all the quantities in one system of units in their fundamental or standard form.

·         Step -3 Simplify and obtain derive unit of the quantity.

Example: To find the unit of velocity.

Velocity is a derived quantity. Hence its unit is a derived unit.

The velocity is given by, velocity = displacement/time

S.I. unit of velocity = S.I. unit of displacement/ S.I. unit of time = m/s

Thus S.I. unit of velocity is m/s

Definitions of Fundamental Units in S. I. System:

1 metre:

·         The unit of length is a metre.  Its symbol is ‘m’.

·         The distance travelled by electromagnetic waves in the vacuum in 1/299, 792, 458 seconds is called 1 metre. The denominator is the velocity of light in the vacuum which is in m/s and is known accurately.

·         One metre is 1,650, 763.73 times the wavelength of orange light emitte by a krypton atom at normal pressure. The wavelength of light is precisely defined in terms of electron transition in an atom, is easily reproducible and is not affected by the change in place, time, temperature and pressure, etc. Hence metre is defined in terms of wavelength of orange light.

1 kilogram:

·         The unit of mass is a kilogram.  Its symbol is ‘kg’.

·         1 kilogram is defined is the total mass of 5.0188 × 1025 atoms of C12 isotopes of carbon. Or The mass of a cylinder made up of platinum-iridium alloy kept at the International Beuro of Weights and Measure is defined as 1 kilogram. Reason for Using Platinum iridium alloy for the cylinder is that it is least affected by environment and time.

1 second:

·         The unit of time is second. Its symbol is ‘s’.

·         1 second is a time duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the Cesium-133 atom. Period of vibration of the atom of Cesium – 133  is used for defining the standard of time because the period of vibration of the atom of Cesium – 133 are precisely defined, is easily reproducible and is not affected by a change in place, time, temperature and pressure, etc.

1-degree kelvin:

·         The unit of temperature is degree kelvin. Its symbol is ‘K’.

·         1-degree kelvin is a fraction 1/ 273.16 of the thermodynamic temperature of the triple point of the water. The triple point of the water is a temperature at which ice, water, and water vapour are in equilibrium.

1 candela:

·         The unit of luminous intensity is candela. Its symbol is ‘cd’.

·         1 candela is luminous intensity in the normal direction of a surface of area 1/600000 m² of a black body at the freezing point of platinum under pressure of 1.01325 × 10⁵ N/m².

1 ampere:

·         The unit of electric current is the ampere. Its symbol is ‘A’.

·         1 ampere is the constant current, which is maintained in each of two infinitely long straight parallel conductors of a negligible cross-section, situated one metre apart in vacuum, will produce between the conductors a force of 2 × 10^-7 N/m.

1 mole:

·         The unit of the amount of substance is mole. Its symbol is ‘mol’

·         1 mole is the amount of substance which contains as many elementary entities (atoms, molecules, ions, electrons, etc.) as there are atoms in 0.012 kg of pure C12. The number of entities in one mole is 6.02252 X 10²³. It is called as Avagadro’s number.

1 radian:

·         The unit of plane angle is the radian. Its symbol is ‘rad’

·         One radian is defined as the angle subtended at the centre of a circle by an arc equal in length to the radius of the circle.

1 steradian:

·         The unit of solid angle is steradian. Its symbol is ‘sr’

·         One steradian is defined as the solid angle that encloses a surface on the sphere of an area equal to the square of its radius.

·         Maintaining Uniformity of Standards

An international body Conference Generale des Poids et Measures or CGPM (General Conference of Weight and Measures) has been given the authority to decide the standards and units by international agreement. It holds its meetings and any change in the standard units are communicated through the publications of the Conference.

India adopted the metric system of units in 1956 by Parliament Act “Weights and Measures Act- 1956”. The function of manufacturing, maintaining, monitoring, and improving the standards of measurements is discharged by the National Physical Laboratory (NPL), New Delhi. The uniformity in standards is maintained as follows:

·         Measures (e.g. balances and weights) used by shopkeepers are expected to be certified by the Department of Measures and Weights of the local government.

·         The working standards of these local departments have to be calibrated against the state-level standards, or any laboratory which is entitled to do so.

·         The state-level laboratories are required to get their standards calibrated from the National Physical Laboratory at the national level, which is equivalent to international standards. Thus, measurements made at any place in the world are connected with the international system.

Prefixes Used in SI System:

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Different Types of Material and Their Properties

An Introduction to Different Types of Material

There are many types of materials that are most commonly used in daily life. The knowledge of different types of materials allows for the comparison of everyday materials, for example, different types of wood, rock, metal, paper, and plastic, according to their properties. 

The properties of material include hardness, strength, flexibility and magnetic behaviour. Different types of material and their properties can be used in the making of many different objects which can be used in day-to-day life. For instance, the hardness of iron, ductility of gold, and silver, the conductivity of copper etc. Let us learn more about such materials and their properties ahead.

 Different Types of Materials 

Biomaterials

A biomaterial is any substance that can be engineered for interaction with biological systems for a medical purpose. For example, they are used for therapeutic purposes, i.e. to treat, augment, repair or replace a tissue function of the body or a diagnostic one. The study of biomaterials is known as biomaterials science or biomaterials engineering. Biomaterials science encompasses the elements of medicine, biology, chemistry, tissue engineering and materials science.

Ceramics

Ceramic is a non-metallic material made up of inorganic molecules. The ceramic is normally prepared by heating a powder or slurry.  So many common ceramics are made up of oxides or nitride compounds, high in a crystalline form with long-range molecular order.  The ceramics are halfway or fully amorphous and with no long-range molecular order. These are typically classified into glassy materials.

Metals

The metals are malleable comparatively. The metals are optically reflective and electrically conductive. Mostly the metals and alloys can be easily shaped by forming. The metals disassociate electron bonding and make them good conductors of electricity and heat. Each metal has an orderly arrangement of atoms, resulting in a crystalline structure that may have multiple crystal phases bordering each other.

Nanomaterials

The nanomaterial is defined as the material with any external dimension in the nanoscale or having an internal structure or surface structure in the nanoscale. The nanoscale is defined as the length range, approximately from 1 nm to 100 nm. This includes both nano-objects and nanostructured materials. 

The nanomaterials are discrete pieces of material, and the nanostructured material has an internal or surface structure on the nanoscale. The nanomaterial can be a member of both these categories.

Wood

Wood is called a composite material. It is made from lignin and cellulose. It uses a lignin matrix and cellulose fibre to form a polymer composite. The lignin helps to hold the cellulose compressively in place so that the cellulose fibre can carry the tensile loads. Wood has excellent structural properties in light of its low weight and high strength.

Different Types of Materials

Different Types of Materials and Their Properties

Materials can also be explained based on their properties. It is important to understand the material's properties to decide whether the material is suitable for its use.  When we talk about a material's properties, we mention the features we can sense, measure or test. For example, if we have any kind of sample of metal in front of us, we can identify what the colour of that material is, whether it is hard or shiny. 

Testing the materials shows that they can conduct heat and electricity and that they will react with an acid. These are some properties of metals, which enable us to identify them

Image Showing Properties of Different Materials

Physical and Chemical Properties

Almost all materials contain physical properties. A physical property is a property that a person can measure without changing the material. Examples of physical properties are colour, amount, hardness, and temperature.

Similarly, materials also have chemical properties. A chemical property tells us how a material will change into a different substance under specific conditions. For example, some metals rust if they are kept out in the rain. Paper and wood burn to ashes if they come in contact with the flame.

Summary

Any type of substance used to make something is known as material. For example, the school desk can be prepared from wood, plastic, or metal or a mixture of all three materials. When any kind of object is designed and made, it is very important to choose the best material for the job. Materials have certain qualities or properties. For example, the properties of materials include strength, colour, and hardness, which must be considered carefully. Some other factors, such as cost and availability, are also important.

FAQs on Different Types of Material and Their Properties

1. What are the materials? Define in short. 

Materials can be natural or artificial. They can be made from living or non-living things. The material that has not yet been used or changed in any way is known as raw material. Natural materials will be exhausted one day so they must be used carefully and replaced wherever possible. This is described as the sustainable use of all resources that come from nature. 

Different types of materials have different kinds of properties. Materials can be soft, hard, flexible ( can be bendable), rigid (can be stiff), transparent (we can see through it), opaque (means the light does not shine through it), rough, smooth, shiny or dull. For example, the glass material is transparent, hard and smooth.

2. Explain the materials from living things and materials from non-living things.

Wood (used for making school benches), paper (used for making books), and cardboard (used for making boxes) all are made from trees. Leather (used for making jackets) comes from cattle skin; wool is made from sheep and cotton is made from plants. All these are the material of living things.

 Metals and precious gems, for example, diamonds, are excavated from rocks in the ground. Materials like chalk, clay, coal and sand are also examples of nonliving things. There are some materials that are a mixture of living as well as non-living things. For example, the soil is made up of tiny organisms, dead plants, stones, tiny particles of rock, air and water.

3. Describe some of the physical properties of metals.

1. Strength - Metals have high tensile strength. 

2. Ductility -  Metals can be drawn into thin wire without breaking.

3. Malleability - Metals can be drawn into thin sheets without breaking.

4. Melting and Boiling Points - Metals have high melting and boiling points.

5. Conductivity - Metals are good conductors of heat and electricity.

6. Lustre - Metals are lustrous i.e. they have a shiny appearance.