All forces that exist and operate in nature and cause many natural events to occur on the earth: usually manifesting in the form of forces such as magnetism, gravitation, sound, heat, electricity and light etc is nothing, but different forms of energy which is the outcome of many changes or transformations that the matter undergoes on Earth. Thus, it can simply be said that the matter is always associated with energy.

Infact, contrary to matter, the energy neither occupies any space nor does it possess any mass. This is the reason that the energy is always described and defined but not in physical terms, but on operational or functional basis only. In this sense, the simplest definition of energy that emerges out is:

“It is the force that brings about a change or motion in matter.” or in other words, “It is the capacity of a material body to do some work or to produce an effect.”

Taking a cue from the above definition of energy, it can be understood that on a primary scale, the energy occurs in two forms or phases called as potential and kinetic energy.

While Potential energy refers to the stored energy of the matter or the energy of position of a material body. The Kinetic energy on the other hand, is the energy of motion or action possessed by a material body. In other words, kinetic energy is the active energy that is used in the process of producing an effect in the matter and hence is used for doing some work. To illustrate, we can take the example of a footballer. The potential energy stored in his leg remains as such until he kicks or hits the ball. But as soon as he hits or strikes the ball with his leg, the potential energy having been stored in his leg gets converted into the kinetic energy thereby, giving motion to the football. In the same vein, to take another example, we can say that a wood log or boulder lying at rest has the potential energy stored in it. Once, it is taken uphill, the kinetic energy involved or spent on carrying it uphill gets stored in it as its potential energy of position or rest. If, now, the same wood log or boulder is being pushed down hill, the so called its potential energy of position gets converted into the kinetic energy that lends downhill motion to the same.

Given thus, it can fairly be concluded that just as the potential energy got converted into the kinetic and vice-versa in the above examples similarly, any form of energy can be converted from its one form to the other and this is true to both living and non-living matter on this earth. This is the reason that we have different manifestations of energy on this earth that may be referred to as heat, sound, light, magnetic and nuclear energy etc. This is what that is the essence of first law of thermodynamics. Yet, it must be noted that during each of such energy transformations there is always a loss of some amount of energy in the form of heat such that no system whether living or non-living has ever been created or found on earth that is 100% efficient and thus, is the essence of second law of thermodynamics. The scientific truth is that the dissipation or loss of energy as heat into the environment is the ultimate fate of all kinetic energy on this planet…

Both laws of thermodynamics and energy transformations from one type to another can best be explained by the following live example:

As we know that a steam locomotive runs the train by using coal as its fuel. Now, the coal that stores its energy as its potential chemical energy which upon burning, gets converted into heat energy. A part of this heat energy dissipates into the environment and is thus, lost. But, the rest of the heat energy is used for boiling the water to produce the steam. The steam stores its energy as potential heat energy which gets converted into the mechanical kinetic energy that then gives motion to the rail locomotive. A part of this mechanical energy however, is also fed into a dynamo to be got converted into an electrical energy that is eventually converted into so called, light energy to light on the bulbs and lamps or for that matter, mechanical energy to run the fans within the train compartments.

What is the basis of matter-energy complex?

In the simplest terms, it can be said that the electrons in an atom represent the matter of the above complex and their revolution around the nucleus in discrete orbits what we call as electron shells, represent the energy reservoir of an atom or matter. Noted that these electrons shells essentially represent the different levels of potential energy owing to the fact of their being manifested in the form of an electric force or charge that actually keeps the negatively charged electrons being bound tightly to the positively charged nucleus. Thus, to conclude that, the electrons, protons & neutrons together, represent the lowest units of the matter (particulate matter) whereas, the discrete electron shells being non particulate in nature, essentially represent the units of energy and this is how a typical matter- energy complex operates and has been operating in nature ever since the evolution of earth and life have occurred on it.

The Three States of the Matter

To have a fleeting reference to the respective states of the matter particularly, in terms of their behaviour, we can say that a gas does not possess an internal boundary and it expands to fill any container completely irrespective of the size or shape of the given container. A liquid on the other hand, possesses one internal boundary what we call as its surface. Therefore, it goes on filling its container below its surface regardless of the shape and size of the given container. In the same vein, a solid being rigid in nature is bounded internally in all directions and dimensions and thus, needs no external container. Now so far as the compressibility of the each matter state is concerned, we can say that a gas is much easier to compress than a liquid which infact, shows its compressibility somewhere in between the gases at one extreme and the solids at the other which means that the liquids are compressible only to a certain extent. However, the solids completely defy the behaviour of their being compressed anymore.

It is rather interesting to note that these discerning properties of the matter have what made them to be the substances of great significance for the mankind and this is where essentially the starting point of our topic- “everyday Physics” can be taken to have actually begun: In this regard, let’s first start with:

The Gaseous state of the matter

As discussed earlier, one of the outstanding properties of the gases is their being compressible in nature. This property of the gases has been explained through the ‘kinetic molecular theory’ of the gases according to which the gas molecules are always in random motion either in a container in which the gas is contained or in open. This random motion of the gas molecules has been possibled due to a large relative or inter-se distance between the gas molecules that permits a large empty space between them such that they always remain in a haphazard random motion. This exactly explains the ease with which the gases can be compressed. The gas molecules being in constant rapid motion move in straight lines until they collide with other molecules of the gas or with that of the walls of the container. This very nature of the gas explains the filling of the containers by gases as well as their mixing up with other gases. Similarly, once the moving gas molecules collide with the walls of the container, they become responsible for causing the pressure of that very container. Infact, the given pressure of a gas or the container as such is actually the result of the number of such collisions happening per unit time and accordingly more the number of such collisions per unit time, more shall be the pressure of the gas which can obviously be increased by forcing more gas into the container or otherwise, decreasing the volume of the gas.

Everyday physics involved in the ‘gaseous’ state of the matter: As we already know that the gas molecules are always in rapid and random motion due to relatively a large distance between the gas molecules. This property of the gases makes them to exhibit a unique physical phenomenon what we call as diffusion.

It is this property of the gases that an incense stick (Agarbatti) or the odour of a perfume kept in one corner of the room fills the entire room with the fragrance or odour in an instant. The diffusion rate of a gas chiefly depends on its molecular weight such that lighter the gas, more rapid shall be its rate of diffusion. One English scientist, named Graham very nicely explained the rate of diffusion of different gases by propounding a law which is today known as Graham’s law of diffusion according to which: “the rates of diffusion of gases are inversely proportional to the square roots of their densities when the respective gases are at the same temperature and pressure.” This law was put to a practical use for the first time while preparing the first atomic bomb. In the said task, the naturally occurring Uranium called Uranium-238 was combined with fluorine gas to form the Uranium hexafluoride gas (UF6). When this gas was passed through a porous membrane such as unglazed porcelain or natural rubber, the molecules of the gas containing the lighter weight uranium isotope called uranium-235 diffused slightly more rapidly through the porous membrane to the other side as compared to the molecules of the gas containing the heavier uranium isotope called U-238. This way, by doing repeated diffusions, the usable fissionable material that is the actual bomb material even now called as U-235 was separated from the useless U-238. This process of obtaining or extracting the useful U-235 from that of the naturally occurring U-238 through a diffusion process that is even well practiced today is called as the enrichment of the uranium and the uranium thus obtained is called as enriched uranium.

Changing gas to liquid and your common cooking gas, LPG is obtained: If the volume of a gas is sufficiently reduced by compressing it or by cooling it or for that matter, by the application of both, the gas will ultimately be condensed into a liquid form. The Physics behind this all is the fact that decreasing the volume of a gas either by compression or otherwise will have the effect of decreasing the average inter-se distances between the gas molecules such that the number of collisions per unit time will be increased thereby they end up loosing their kinetic energy that is the energy of their motion and hence, condense into a liquid form. Similar is the effect of cooling a gas as it also amounts to decreasing their kinetic energy and thus, making a gas to liquefy. However, we have a number of substances existing in the gaseous state at room temperature that can be condensed to a liquid state by the application of pressure alone. But there do exists certain gases that resist liquefaction regardless of the pressure imposed thereon and hence, liquefy only after being subjected to cooling or low temperature treatment. This can be explained by the fact that a critical temperature is always involved in the liquefaction process of a gas. And a critical temperature of a gaseous substance is the temperature above which it is impossible to liquefy the substance by pressure alone and the pressure required to liquefy a gas at its critical temperature is called the critical pressure. The more a gas is cooled below its critical temperature, the less pressure will be required to liquefy it. In fact, any substance existing in a gaseous state at a temperature above its critical temperature is what exactly & properly called a gas. For the purposes of our common household cooking gas, LPG which is essentially a hydrocarbon of a saturated type called as butane exists as a gas in its physical state and has been liquefied by the application of pressure and temperature both and thus carries a weight and stored in a container called a cylinder. So is true of another gas liquefied in a similar manner called as CNG that is being used as a clean automobile fuel in most of our metros.

Liquid hydrogen as fuel & ‘Hydrogen Economy’: It is no surprise that on a mass for mass basis, hydrogen as fuel can release far more energy than petrol (about three times) and that too without emanating any pollutants into the air during combustion. Yet, the only stumbling block on the way of its being used as a universal clean fuel are the troubles associated with its storage. As a cylinder of compressed hydrogen weighs about 30 times as much as a tank of petrol containing the same amount of energy. As the hydrogen as a gas can be converted into its liquid state by cooling it to 20K that would require highly expensive insulated tanks for its storage. Such tanks are being made from expensive metal alloys like that of NaNi5, Ti-TiH2 or Mg-MgH2 etc and are practically in use currently for storage of hydrogen in small quantities. Owing to such handicaps and limitations associated with hydrogen as a fuel, has eventually prompted the researchers to look out for some alternative techniques that would ensure its use as a fuel in a far more efficient manner and hence, the alternative of what we call as ‘Hydrogen Economy’ came to the fore. Hydrogen economy literally refers to the use of liquid hydrogen as fuel. In essence, the basic principle of hydrogen economy is the storage and transportation of this form of energy as liquid or gaseous dihydrogen and this is where that the advantage of its being used as a fuel lies in. As the hydrogen economy will ensure that the energy is transmitted in the form of hydrogen rather than as electric power. Keeping this advantage in view that it is for the first time in the history of India, a pilot project using hydrogen as fuel was launched in October 2005 for running automobiles. In this case, initially 5% hydrogen has been mixed in CNG for being used as a fuel in four-wheeler vehicles and this %age would later be increased gradually to reach the optimum level. Hydrogen nowadays is also being used in ‘fuel cells’ for the purposes of generation of electricity. Lets hope that in the years to come, some more economically viable and safe sources of hydrogen would be made available to make its use as a common & universal source of energy…

Working on Gases/ other material at extremely low temperatures: The Science of “CRYOGENICS”: Cryogenics, the word is derived from cryo= cold and genics= to produce, is the new emerging science of working on gases (matter) at extremely low temperatures at which gases are reduced to a liquid state and other materials change their inherent properties. Cryogenics has immense applications in a host of diverse fields right from rocket/ space technology to medicine including preservation & many others as are being mentioned in the table given herein below:

Connecting concepts: UTILITIES OF CRYOGENICS in Everyday Life!

Deep Cryogenics: It is the ultra low temperature processing of materials to enhance their desired metallurgical and structural properties. The hardness of the material treated is unaffected, while its strength is increased. The materials so treated greatly increases the strength and wear life of all types of vehicle components, castings and cutting tools. In addition, other benefits include reduced maintenance, repairs and replacement of tools and components, reduced vibrations, rapid and more uniform heat dissipation, and improved conductivity.

Cryobiology: The world cryobiology (Greek cryo, “cold”, bios, “life” and logos, “science”) literally signifies the science of life at low temperatures. In practice, this field comprises the study of any biological material or system (e.g. proteins, cells, tissues, organs, or organisms) subjected to any temperature below normal (ranging from moderately hypothermic conditions to cryogenic temperatures).

Cryocooler: A mechanism that can extract heat from an object (cooler) and by doing so draw its temperature down below approximately 150 Kelvin (cryo). Some areas of applications for cryocoolers are: (i) Military – Infrared sensors for missile guidance and tactical applications; infrared sensors for surveillance (satellite based). (ii) Police and security- Infrared sensors for night vision and rescue. (iii) Environmental – Infrared sensors for atmospheric studies of ozone hole and greenhouse effects; infrared sensors for pollution monitoring; (iv) Commercial – Cryopumps for semiconductor fabrication; high temperature superconductors for cellular-phone base stations; superconductors for voltage standards; semiconductors for high speed computers; infrared sensors for NDE and process monitoring. (v) Medical – Cooling SC magnets for MRI systems; Squid magnetometers for heart and brain studies; liquefaction of oxygen for storage at hospitals and home use; cryogenic catheters and cryosurgery; (vi) Transportation – LNG for fleet vehicles; SC power applications (motors, transformers, etc.) (viii) Agriculture and biology – Storage of biological cells especially, pollen grains & seeds and specimens.

Cyro-insulation of Superinsulation: The term “superinsulation” has a number of different meanings to people in different technical areas. To the cryogenic engineer superinsulation typically means many layers of alternating reflective films and low-conductivity spacers, or multilayer insulation (MLI). Vacuum insulation panels for appliances are sometimes referred to as superinsulation.

Space Cryogenics: Space cryogenics is the application of cryogenics to space missions. Many of these missions use infrared, gamma ray, and X-ray detectors that operate at cryogenic temperatures. The detectors are cooled to increase their sensitivity. Astronomy missions often use cryogenic telescopes to reduce the thermal emissions of the telescope, permitting very faint objects to be seen. A broad range of cryogenic technology is needed to support these missions. Another area of space science which makes use of cryogenics is sample preservation. This includes the preservation of biological samples from experiments, on the Shuttle and the Station and the preservation of material gathered from comets, asteroids and other planets.

Cryosurgery: Cryosurgery is an important minimally invasive surgical technique. It can be applied to any procedure in which scalpels are used to remove undesirable tissues.

Wind Tunnels: As used in cryogenic wind tunnels, cryogenic technology is making a major contribution to experimental aerodynamics.    

Liquid Carbon dioxide converted to solid CO2 & formation of ‘Dry Ice’: Once the liquefied CO2 is allowed to expand rapidly, the same can be made to solidify as a solid to what we call as dry ice. Dry ice is used as a refrigerant in refrigeration especially for ice cream and frozen food. However, in the filmdom, extensive use of dry ice is made for the construction of film sets portraying a snow clad mountainous panorama.  

The Liquid State of the matter

A liquid is always noted for having a fixed volume, but no fixed shape. This is owing to the property of its molecules being not located at fixed positions and are thus free to wander about, but within the body of the liquid only for, they can not escape out unless, they are at the surface of the liquid.

In terms of the kinetic theory model as is applicable to the gaseous state also, a liquid and its state of the matter is shown to possess the following fundamental characteristics:

• There are appreciable forces of attraction between and amongst the molecules of a liquid.
• The molecules of a liquid are relatively closer together as compared to the gases whose molecules are far apart.
• The molecules of a liquid are also in constant rapid and random motion.
• The average kinetic energy of the liquid molecules in a given sample is proportional to the absolute temperature.

To surmise the above characteristics of the liquid state of the matter, it can be inferred that the liquids, unlike the gases are known to possess a definite a volume such that they maintain their volume regardless of the shape or size of the container. In liquids, since the molecules are close together so that the mutual forces of attraction are quite strong in them that do not allow its molecules to remain too free to occupy any space. The inter-se closeness of the liquid molecules also provides an explanation to the fact that the density of a liquid is about thousand times greater than that of the density of a gas under comparable conditions. So far as the compressibility of the liquids is concerned, it is also very much less as compared to the gases just because, a very little space is freely available to the liquid molecules so as to become amenable to a force of compression. Although, like the gases, the liquids also exhibit the phenomenon of diffusion, but they diffuse rather very slowly as compared to the gases. This is attributed to the inherent nature of the liquids as the liquid molecules have less inter-se space and are thus, subjected to a number of collisions between them that amount to having a retarding effect on their movement and hence their diffusion.

Everyday Physics involved in the ‘liquid’ state of the matter:

• The phenomenon of evaporation & its cooling effect on our body:
• Why does evaporation always accompany a cooling effect? The phenomenon of evaporation is probably quite familiar to all of us. Like boiling, evaporation is a case of a liquid changing to a vapour form. But then unlike boiling, evaporation is a phenomenon that takes place at any temperature and again unlike boiling too, evaporation is a surface phenomenon i.e. it always takes place at the surface of a liquid.

According to the Kinetic Molecular Theory, the molecules of a liquid are free to move about under the surface of the liquid under the influence of kinetic energy which they possess( kinetic energy) at any given temperature. The amount of this energy possessed by each molecule of the liquid is not uniform however. In general, most of the molecules of a liquid have about the same amount of energy, but some possess appreciably more than average energy and some possess appreciably less. Furthermore, because the molecules in a liquid are so close to one another that they end up colliding frequently with each other such that during each of such collisions energy is redistributed between the colliding molecules thereby, causing a gain in energy in one of the molecules and a loss of energy in the other. This transfer of energy by collision can result in the formation of relatively high-energy molecules. Now the temperature is a measure of the average energy of a sample of liquid. If the temperature goes up, the average energy of the liquid goes up. Similarly, a decrease in average energy results in a lowering of the temperature of the liquid sample.

Since the escape of a liquid molecule in the evaporation process requires energy. Consequently, only those molecules of high energy can evaporate from a liquid. But the escape of these high-energy molecules results consequently in the lowering or decrease of the average energy of the liquid sample. Thus is the rationale that a cooling effect always accompanies evaporation and hence, we cool our body as a consequence of sweating during sweltering and scorching summers…

Interestingly of course then, as soon as the temperature of the liquid begins to drop below the temperature of the surrounding atmosphere, the atmosphere begins to warm the sample and thus, add up more energy to the liquid to replace the energy lost by evaporation. This additional energy, plus the accumulation of it by relatively a few of the liquid molecules through molecular collisions, permits the evaporation of the liquid to continue until ultimately all of the molecules of the liquid have gained enough energy to evaporate and hence, evaporation always remains to be a continuous and spontaneous phenomenon.

• Surface Tension and the rise of water in plants: The molecules of a liquid are so close with respect to each other that they exert appreciable gravitational attraction on one another. Inside the body of the liquid, where a given molecule is completely surrounded by other molecules, these attractive forces are equal in all directions. Thus, they counteract one another, and no net unbalanced force remains on the molecule. However, on the surface of the liquid a molecule is not completely surrounded by nearby relatively vacant. Such a molecule is attracted by its neighbours on the surface and by the molecules below it. This results in a net unbalanced attractive force directed into the interior of the liquid. The effect is that the surface molecules form an encasing film on the liquid which is relatively quite tough. This behaviour is attributed to what is known as surface tension. We can readily observe the effects & phenomenon of surface tension exactly in live action in some of the most visible examples:
• A tiny droplet of water remains intact to assume the shape of a tiny spherical droplet and thus, does not spread out to form a smooth film on a table top because, the surface film holds the water back from ‘seeking its own level.’
•  Drops of water falling free and passing through air are drawn up into spheres by the surface film. A sphere, of course, is a shape containing a maximum volume within a minimum surface.

Connecting concepts: How does water rise to the top of a tree from the roots embedded down in the soil?

Biologists ascribe this all to ‘Transpiration pull’, also referred to as the ‘Cohesive force of water theory’. This theory was proposed in the year 1894 by two scientists named Dixon & Jolly and is based on the following two phenomena of Physics and thus, has essentially the science of Physics behind:

No.1) Transpiration pull exerted on the water column: As water is lost due to evaporation to the intercellular spaces from the "mesophyll cells” of the leaves as a result of transpiration, the same water as vapors is then lost to the outside from the leaves through their stomata. The said vaporized loss of water from the leave’s mesophyll cells causes an increase of DPD. The said increased DPD ultimately causes the mesophyll cells to suck in more water from the adjoining cells and the same is absorbed by them from the xylem vessels of the leaf that are always remain filled with a continuous column of water. As the water is being withdrawn from them, a tension or pull which in Physics resembles the surface tension and herein the context is called as the transpiration pull, develops at the top of the said water column and soon is transmitted down from the petiole of the leaves to the stem and finally terminates at the roots thereby leading to an upward movement of the water…

No.2) Cohesion property of the water molecules so as to form an unbroken water column in the xylem: As xylem tracheids and trachea are long tubular structures extending right from roots up to the leaves such that one end of xylem (continuous with another) is in the root and the other end is in the leaves. These tubes are always remain filled with water wherein the water molecules are tightly held together because of a cohesive force between them and are thus responsible for forming a continuous water column. Whereas, the presence of hydrogen bonds among water molecules provide a strong cohesion that thus holds together a chain of water that in fact extends throughout the entire length or height of the plant within the xylem. It is no surprise to hold that the said water column within the xylem as a result of cohesive forces is as much strong and unbreakable as a steel wire of the same diameter and this is what that is ensured by the cohesion part of the story of the Physics. However, supplementing the cohesion property of the water molecules here is the adhesion property of the force that develops between the water molecules and the walls of the xylem vessels. The attraction of the water molecules to the cell walls of the thin xylem tubes helps the water to creep upwards besides preventing the force of gravity from draining the water column out of the xylem vessels.

Thus, to conclude that the water ascends to the top of the tree because of transpiration pull and this column of water inside the xylem tubes remains continuous because of the cohesive forces of the water molecules….

Surprisingly enough, we can float razor blades or needles on a water surface even though; these objects are far denser & heavier than water just because, the tough surface film of a liquid that acts like a typical leather membrane due to the phenomenon of surface tension, supports them on!

What affect does soap have on the surface tension of water?

Since, the surface tension of a liquid may be changed or better said, reduced by dissolving a substance in the same and so does the effect of soap on water. Say for example, when the soap or a detergent is dissolved in water, it greatly reduces the surface tension of water by causing a decrease in the horizontal forces of attraction that the original water surface had, but by the dissolution of the soap. The result being the formation of net unbalanced forces on the water surface that remain directed away from the point of application of the soap and hence, we are able to wash up our clothes….

Adhesion and Cohesion property of water & maintenance of a water tight column from roots to the last tip of a plant: Surface tension is related to another phenomenon associated with liquids. Between the molecules of a liquid there are attractive forces which may be called forces of cohesion. Similarly, there are attractive forces between the molecules of a liquid and the molecules of its container. These are being referred to as the forces of adhesion. If the forces of adhesion are greater than the forces of cohesion, the liquid will be drawn up into a small-diameter tube made of the substance. If the liquid does not wet a substance, a small-diameter-tube made of the substance will depress the surface of the liquid.

Capillarity & its Physics in live action: The rise or depression of a liquid surface in a small-diameter tube is known as capillary action. The amount of change in the level of the liquid in the tube is directly proportional to the surface tension of the liquid.

Capillary action and Everyday Physics: The sub-surface water in fields is carried up to the roots of plants through tiny pores (capillary tubes) in the soil. A sponge ‘drinks’ water into its capillary tubes. Oil rises up a lamp wick, blotting paper blots or sucks ink, a towel gets wet even if only a corner of it dips in water and so on are the live examples of what we call as capillarity…

Viscosity & the flow of liquids: Why do liquids like honey or seed oils flow slower than liquids like water or milk? Contrary to solids, liquids flow when a stress is applied. This flow results because, intermolecular forces what we also call as attractive intermolecular forces in liquids are largely incompressible. Some liquids like castor oil and honey flow slowly while other, such as kerosene, flow rapidly. These differences in flow rates result from a property known as viscosity. Viscosity in essence, is the resistance offered by a liquid to flow. It may be called as fluid friction. Stronger the intermolecular forces, higher is the viscosity. When the temperature is raised, the viscosity of liquids decreases. This is because; increase in temperature increases the average kinetic energy of molecules which overcomes the attractive forces between them. Heavier and large molecules flow less easily than the lighter and smaller molecules; spherical molecules offer less resistance to flow than plate-like molecules. Molecules with flexible chains offer a very high resistance to flow because of entangling of side chains. Impurities invariably increase the viscosity of a liquid. As noted above, since the substances like honey and oils are comparatively made up of larger and heavier molecules of sugar (fructose) and fatty acids respectively and thus, are noted for having a comparatively stronger intermolecular forces and thus, flow slower than water or any other similar liquid…

Conversion of a Liquid to a Solid: The formation of ice from water:

Connecting concept: Why does ice float on water? When liquids are sufficiency cooled they will congeal to a solid state. The temperature at which a substance solidifies from the liquid state is known as the freezing point of that very substance. As in the case of the boiling point, the atmospheric pressure also affects the freezing of a liquid which expands on cooling. So far as the formation of ice from water is concerned, there is a very unusual property of water than comes into play. This lies in the fact that water always contracts and hence, becomes denser when cooled to 4 degree centigrade. But, if it is subjected to cooling temperature less than 4 degrees, it expands and become less dense. It is said that when water is being cooled to below 4 degrees, it exhibits an unusual property of expansion and thus, becomes less dense that amounts to its being lighter. Thus, it is concluded that ice obviously being less dense as compared to the liquid water below it and hence, it floats. Probably, water is one of the few substances that do not shrink when changed from liquid to solid rather, it expands so much so that when water is frozen into ice, it expands by one-ninth meaning thereby that nine litres of water will give us about ten litres of solid ice! Taking a cue from this all, we may conclude that why do automobile radiators or water pipes burst or crack in chilling winters? Because, the freezing water does not provide any room to the expanding ice thus formed!

The Solid State of the matter

Solids are characterized by their high density and low compressibility compared with those of the gas phase. The values of these properties for solids indicate that the molecules (or ions) in them are relatively close together. Solids can very easily be distinguished from liquids by their definite shape, considerable mechanical strength and rigidity. These properties are due to the existence of very strong forces of attraction amongst the molecules (or ions) of the solids. It is because of these strong forces that the structural units (atoms, ions, etc.) of the solid do not possess any translatory motion, but have only vibrational motion about their mean positions. Solids maintain definite volumes independent of the size or shape of the container in which they are placed. Solids diffuse very slowly compared to liquids or gases. Particles constituting solids occupy fixed positions.

Classification of Solids: Different structural features of solids can form the basis for classifying them. They may be roughly divided into two classes: true solids and pseudo solids. A distinctive feature of solids is that they are rigid. A true solid has a shape which it holds against mile distorting forces. A pseudo solid lacks this character. It can be more easily distorted by bending and compressing forces. It may tend to flow slowly even under its own weight and lose shape. Pitch and glass are two examples of pseudo solids.

Connecting concepts: What’s Glass? In general terms, the Glass represents an example of a pseudo-solid that means its solid character, rigidity or shape is only apparent otherwise, in actuality, it is as good as a liquid which tend to flow under its own weight and thus, can easily change its shape. At the same time, a glass entirely lacks the character of a true solid like that of rigidity and being not amenable to distorting or bending forces. This is the reason that a Glass is described as a pseudo or false solid. For example, you might have observed that in old buildings, window panes (glasses) are found to have become somewhat thicker at the bottom and thinner near the top that indicates the fluid nature of a solid like Glass. In essence, such substances like Glass are better described as “super cooled liquids”. Infact, pseudo solids do not melt sharply on being heated instead, they gradually soften over a wide range of temperatures and eventually, lapse into a liquid state. At the same time, it must be noted that a solid like Glass do not have a definite & defined melting point coupled with its lacking a definite geometrical pattern due to a random arrangement of its constituent particles, it is also referred to as a vitreous or an amorphous solid…

 Solids may either exit in ‘shapeless amorphous’ form or in a ‘well-shaped crystalline’ form. A brief description of the same is being given herein below:

Crystalline solids are characterized by the regular arrangement of atoms, ions or molecules in all the three dimensions. This regular arrangement gives rise to long range order in crystals. The definite pattern constantly repeating in space is such that having observed it in some small region of the crystal; it is possible to predict accurately the position of particles in any region of the crystal, however far it may be from the region under observation. The constituent particles in crystals are generally held by strong inter-atomic, inter-ionic or inter-molecular forces. When we try to cut a crystalline solid with a sharp-edged tool it gives a clean cleavage. Crystalline substances have a definite rigid shape or morphology. Every crystal is contained within a well-defined set of surfaces which are called planes, faces, intersect an edge is formed. When heated, the crystalline solid melts at a specific temperature called the melting point of the solid.

Connecting concepts: ‘Quartz’- the most widely distributed & useful of crystalline solids: Another name for quartz is silica as it is made up of silicon and oxygen and by nature, is harder than steel and clearer than glass. As a mineral, it is generally found in large, clear six-sided crystals with pyramid like ends what are called as “rock crystals.” Infact, some of the most abundant rocks are composed largely of quartz. As such, the sandstone consists of nothing, but composed of the grains of quartz held together by a cementing substance. Quartz otherwise, forms a large part of the rock what we call as granite. However, white sand is almost pure quartz whereas; all sands are largely made up of quartz only. Semi-precious stones such as Agate, Amethyst and Onyx are nothing but quartz. In terms of its use, Quartz finds its extensive applications in the manufacture of a number of optical instruments and glass. Notably, the thin slices of pure quartz are being cut for being used in radio-broadcasting so as to ensure the radio stations being on their proper wavelengths. Sometimes, special quartz lamps are being used to give artificial sun treatments.

Amorphous solids include other substances like fused silica, rubber and polymers of high molecular masses. They may even have small parts in crystalline and the rest in non-crystalline form. Crystalline parts of otherwise amorphous substances are called crystallites.

Properties of Solids: The special use to which we put different kinds of matter is dependent, in the last analysis, on the forces between molecules of a particular matter substance. Say for example, the forces of cohesion that show up when the distance between molecules is very small and that are especially strong in solids. These cohesive forces in solids are thus, responsible for many of the useful properties of solid materials that we make use of both in industry and everyday life.

Why do we need to weld the solids, like metals? One of the most obvious attributes of a solid matter is its resistance to being pulled apart. This is what we call as ‘tenacity’ or tensile strength of a solid. It takes a force of over 200 tons to pull apart a good quality steel rod of just 1 square inch in cross-section. This is what makes and has made the steel so useful in structural engineering since ages. If the two pieces of a broken specimen, say steel or an iron rod are pressed together again they no longer stick together, because we cannot get the molecules on both sides of the break close enough together to make their cohesive forces effective enough so as to make them realign into a complete rod again. However, by heating the pieces and pounding them together they can be welded into the one. Infact, we do have some solids that have a very low tensile strength, but have a strong resistance to crushing and stone falls in this category of solids. This is what makes the stone a very useful material solid for building arches and piers, where it bears compressive stresses only.

Another widely used property of solids is their elasticity. It is the ability of a substance to recover to its original shape and size after distortion or as soon as a distorting force is removed thereof. If a strip of steel or bronze is given a moderate twist or bend or stretch, it returns to its former/original shape after the distorting force has been removed. This property makes such metals as being very useful for making springs.

What is Hooke’s Law? When a solid body is stretched what we describe in Physics as “stress”, its molecules across any section will attract each other and exert a restoring force. Thus, a stress is defined as the restoring force per unit area. On the other hand, “Strain” means, distortion and is defined as the change in dimension per unit of original dimension. Robert Hooke (1635-1703) as a result of a number of experiments found that “within the limits of elasticity, strain is directly proportional to stress.” This is known as Hooke’s law. Thus, the elongation of a wire is directly proportional to the stretching force on it.

Grease or putty shows no tendency to recover to its shape after being deformed i.e. it completely lacks elasticity and such substances are thus, said to be highly plastic. But even steel, if stressed more than a certain amount, will fail to return completely to its original shape. This conveys the sense that all structural materials should never be required to work as far as these limits.

Although some substances can easily break if stretching (tensile) forces are applied on them. However, they can support large weights or forces of compression. Such substances are called brittle substances e.g. masonry, cast iron, etc.

Over and above this all, there are several other useful molecular properties of solids. Certain metals, such as gold, copper etc, are very malleable – that is, they can be pounded or rolled into very thin sheets. Gold can be beaten into sheets that can even be about 1/5000 inches thick. Other metals, such as copper, platinum and silver can be drawn out into very fine wires. They are said to be ductile. Wires less than one-hundredth of the thickness of a hair strand can be made out of platinum. Similarly, it is also not surprising to know that a mere 30 grams of silver can be drawn into a wire more than 30 miles long…

Connecting concepts: How hard a solid can be? The hardness of a material is measured by its ability to scratch other substances. Diamond is the hardest ever known substance on the Earth. The formation of diamonds on earth can be traced to the hoary past when the evolution of the earth took place. A hundred million years ago, the earth was in its early cooling stages. At that point of time, there existed beneath the ground a mass of hot liquid rock. The said mass that predominantly had carbon in it was subjected to extreme heat and pressure and hence, it was this carbon that became what we called “diamonds.” Undoubtedly, diamonds are the hardest natural substance ever known to man, but then the question arises as how do we measure the hardness of a particular substance? Well, one way of doing this all is by using the scratch test that involves the scratching of diamond with another hard substance.

In 1820, a man called Mohs made up a scale of hardness for minerals based on such a test. Based on his scale what is now known as Mohs scale, the hardness of various minerals was determined in the following order starting from the lowest to the highest: (1.) Talc. (2.) Gypsum. (3.) Calcite. (4.) Fluorite. (5.) Aphatite (6.)  Feldspar. (7.) Quartz. (8.) Topaz. (9.) Corundum (10.) Diamond.  On the Moh scale, it was determined that Corundum is at number 9 on the scale in terms of the hardness whereas, Diamond stands at number 10 on the same scale and hence, emerges as the champion for hardness with no competition from anywhere to assail its hardness. Now the second question arises that since diamonds are so hard, how can they be shaped and cut? Interestingly, the only thing that can cut a diamond is but, another diamond only. Infact, what diamond cutters use is a saw with an edge made of diamond dust only. In India, Surat in Gujarat is a world famous destination for diamond cutting. In the same context however, diamond grinding and cutting wheels are used in industry in many ways, such as to grind lenses, to shape all kinds of tools made of copper, brass and other metals and of course, to cut glass. Today, more than 80% of all diamonds produced are used in industry. 

Plasma (Fourth State of Matter): It is a well known fact that matter be it solid, liquid or gas, is neutral in regard to electric charges. But strangely, most of the matter in the universe exists in a special kind of gaseous state in which the atoms are in fact split and the electrically charged particles are disengaged. Matter in this ionized condition is called plasma which is becoming increasingly important in electronic devices, in the search for thermonuclear power and as a source of electric power.

The branch of science dealing with the use of plasma to generate electricity is called magneto-hydro dynamics. This method is admirably suited to countries with plenty of coal supply and is, therefore, advocated by countries like Poland which consider the power produced thereby to be cheaper than atomic energy.

Connecting concepts: In the whole Universe Seven States of Matter exist!

Our everyday experience of things tells us that matter on earth exists in three distinct forms – solid, liquid and gaseous like liquid water appearing sometime as solid ice and sometime as gaseous stream. But when we consider all matter in the universe as a whole, we find that it exists in several other states not ordinarily encountered on earth. Although, these states of extra-terrestrial matter are very varied, they may be broadly classified into four basic kinds other than three states that exist on Earth. They are plasma, degenerate, Neutron and black-hole states of matter.

“Plasma state” is the state of matter when its temperature is so high that it ceases to remain as a hot gas. Instead, the atoms of the hot gas are split apart into their constituent electrons and nuclei to make it a glowing plasma. Plasma, therefore, is a hot gas of electrically charged particles like free protons and electrons. This is the state of matter of which stars like our very own sun are made.

“Degenerate” state is the state of matter of which stellar corpses called white dwarfs are made of. White dwarf is the terminal stage in stellar evolution when a moderate sized star has completely burnt out its resources of nuclear fuel and can no more produce the energy with which it shines. Matter in “degenerate” state is so dense that a match box full of it weighs several tons.

“Neutron” state is the stuff of the debris that a massive star leaves behind when it explodes as a supernova. Neutron stars are even denser than white dwarfs.

Finally, “black-hole” state is that speculative condition of matter when millions of stars are packed within the eye of a needle! It is, therefore, so infinitely dense that its gravity traps even its own rays of light that what it emits is virtually invisible.

It is that “singular” state of matter where almost all its diverse attributes disappear not unlike the grin of the vanished Cheshire cat in Alice in Wonderland….

What’s the ‘Ultimate State of Matter’?

The three states of matter – solid, liquid and gas – we are all familiar with, is not the whole story. We know that each of three states gives rise to the next by heating like ice turning into water and water into steam. But physicists have now discovered that new states arise when temperatures are raised still further. At several thousand degrees gas will ionize into a plasma with all its atoms broken into their nuclei and satellite electrons. At several million degrees, the atomic nuclei in turn, are broken into individual protons and neutrons. At still higher temperatures even these nuclear particles fragment into “quarks” of which neutrons and protons are made.

At each successive phase transition, some structure is lost. Solid ice loses its crystalline structure on melting into water. Boiling water becomes a chaotic mélange of molecules, and with higher temperatures the molecules and eventually the atoms themselves fragment into sub-nuclear particles. Is there an ultimate limit to this continual fragmentation? Do the sub-nuclear particles like quarks and leptons fragment further to give rise to yet another state of matter?

Some theoretical physicists believe so. According to their speculation, the ultimate state of fragmented matter is that weird condition with which our universe originated with a big bang some 15-20 billion years ago. They believe that at the instant of the big bang the ambient temperature of the universe was more than 10³⁰ degrees K. Under these Draconian conditions, matter appears in its primeval state of fragmentation smashed into its ultimate building blocks with the complete obliteration of the individual identities of even quarks and leptons.        

All the manifold diversity of present-day matter was merged into a single ultimate state at the instant of creation. In exactly the same manner all this four fundamental forces of nature-gravitation, electromagnetism, weak and strong – that control the structure of our existing macro and micro world merged into a single unified force with physics reduced to its basic simplicity.

Alas! Theoretical physicists have yet to discover this ‘simple’ law of unified force. All that their theorizing has become able to do so far is this. First the temperature of the primeval fire ball plummeted from quasi-infinite values at the outset to a mere 10¹⁰ degrees K within one second! For about the brief span of 10^-35 second the temperature could have been 10³⁰ degrees K., high enough for the predicted ultimate phase of matter to have had a fleeting existence. Obviously, we will never be able to duplicate temperatures of this order to see what such an ultimate state of completely fragmented matter looks like…

Solutions & everyday Physics involved in them

A solution consists of two components – a solvent, which is the dissolving medium, and a solute, which is the substance dissolved in a solvent. Solutions are mixtures, because an infinite number of compositions involving a given solute and solvent are possible. In a solution, the solute is dispersed into molecules or ions and the distribution of the solute is perfectly homogenous throughout the solution.

A concentrated solution is one which contains a relatively large amount of solute per unit volume of solution. A dilute solution on the other hand, is the one which contains a relatively small amount of solute per unit volume of solution. The principal methods of expressing the concentration of solutions are molarity, normality, parts per million (ppm) etc. A standard solution is any solution of accurately known concentration.

Solutes may be divided into two classes: (i) Those which when dissolved in water produce a solution which conducts an electric current are called electrolytes; acids, bases and salts belong to this class. (ii) Those which when dissolved in water produce a solution not capable of conducting an electric current are called non-electrolytes.

• Why does a solution, say a sugar solution, boils at a higher temperature than pure water actually do?

This has something to do with an important phenomenon exhibited by the liquids what we call as vapour pressure. Since, the pure water or solvent always has a higher vapor pressure as compared to a solution owing to the fact that when a solute is dissolved in a solvent say, water, the given solute takes up a portion of the solvent’s surface where otherwise, in a pure solvent, only water molecules of high energy have occupied the surface space.

This consequently, has the effect of decreasing the number of molecules of solvent in contact with the air above it, and consequently, reduces the rate at which these molecules could escape out as vapours. The extent to which a given solute lower the vapour-pressure of their solvents depends upon their very concentration in the solution.

 Now given the fact that a solution has a lower vapour pressure than the pure solvent, it explains another phenomenon associated with solutions, namely, that the boiling point of a solution is higher than the boiling point of the pure solvent and this is again attributed to the fact of their being a discrete difference in the vapor pressure of the two…

In the same vein, a solution freezes at a temperature far below the freezing point of its solvent. This phenomenon is likewise, related to vapour pressure too.

This difference in the vapor pressure has found its unique application in the operation of various types of drying agents we may use in our cupboards during moist seasons or climates.

• What is the principle of action of various drying agents or desiccants?

 If a dish containing pure water and one containing a solution are placed side by side inside a tightly covered container, each liquid will begin to emit vapour into the air inside the container such that the air will become saturated with vapours relative to the solution first. Thus, any additional vapour emitted by the water will condense back to liquid in the solution. Consequently, the air never gets a chance to become saturated with vapour relative to the water, with the result that all of the water eventually finds its way into the solution. This process is known as isothermal distillation. This phenomenon is the principle of operation of the various drying agents used in the cupboards of homes in moist climates. Solid chemicals, such as calcium chloride or potassium carbonate, which are very soluble in water, become moist in damp air. A saturated solution forms on their surface. The vapour pressure of this solution is less than the vapour pressure of the water in the moist air, and so more moisture is absorbed by the solution. Ultimately all of the solid dissolves in the moisture it absorbs, but even so, the solution continues to absorb moisture until the vapour pressure of the solution equals the pressure of the water in the atmosphere. This phenomenon is known as deliquescence and deliquescent chemicals used as drying agents are called desiccants.

You are, of course familiar with various applications of the lowering of freezing points. Alcohol or ethylene glycol (permanent anti-freeze) is added to the radiators of cars to lower the freezing point of the water. If a path is icy, salt is sprinkled on it. The salt dissolves in the little water on the surface of ice forming a salt solution, the freezing point of which is lower than that of water, the ice, consequently, melts to go into solution.

What are Colloids?

Colloidal particles were once thought to be non-crystalline and thus, they were given the name ‘colloid’ which means glue-like. However, colloidal particles may be either crystalline or non-crystalline in true sense of the term. When colloidal particles are dispersed in a gas, liquid, or a solid, the result is called a colloidal system. It is impossible to have colloidal particles of a gas dispersed in a gas. Gases disperse in gases in the form of small molecules producing a homogeneous mixture or a solution. It is not classed as a colloid which is heterogeneous.

Sol: Name given to a colloidal system in which a solid is dispersed in a liquid. The system shows all the characteristic of a colloid, and the particles of sol will not settle out.

Gel: In a gel, the liquid contains a colloidal solid evenly dispersed throughout the system but set in a structure which will not flow. Typical examples of a gel are jellies and gelatin.

Aerosol: An aerosol is a dispersion of either a solid or a liquid in a gas. When the dispersed colloidal particle is a solid, the result is smoke. The smoke from the factory may contain fine ashes and particles of unburnt fuel suspended in exhaust gases. When the colloidal particles dispersed in the gas are liquid, the resulting aerosol is a fog. When the dispersion media is water, colloids are known as hydrosols; when the dispersion medium is alcohol, the colloids are known as alcohols and in benzene they are known as benzosols.

Emulsion: An emulsion exists when colloidal particles of one liquid are dispersed throughout in another liquid in which it is not soluble.

The process of making an emulsion is termed emulsification. Emulsions are of two types, the oil-in-water type and water-in-oil type. The droplets in emulsion are some what larger than usual particles found in sols. Emulsions may be produced by vigorously agitating a mixture of the liquids, or better by subjecting the mixture to ultrasonic vibration. Emulsions are generally unstable unless a third stabilizing substances, known as emulsifying agent, is also present. In the absence of emulsifying agent, the dispersed droplets coalesce and eventually the emulsion breaks up into layers. The most frequently used emulsifying agents are soaps and detergents. Their emulsifying properties help in washing of clothes and crockery by emulsifying the grease and carrying it away in the water along with dirt. Some of the industrial uses of emulsions are in concentration of the ore, etc. They are also used in salad dressing. Milk is a natural emulsion of liquid fat in a watery liquid. Paint otherwise, is called a synthetic emulsion.

Macromolecular Colloids: In this type the dispersed particles are themselves large molecules. They have very high molecular masses. They are usually polymers, for example, synthetic rubber.

Micelle: There is another type of colloids which behave as normal, strong electrolytes at low concentration, but at higher concentrations exhibit colloidal state properties. There are known as micelles. Such substances are referred to as associated colloids. Soaps and synthetic detergents belong to this class.

Properties of Colloids: Like solute particles, colloidal particles also diffuse, though slowly from a region of higher to a region of lower concentration.  

Colloidal particles tend to settle down very slowly under the influence of gravity. The rate of sedimentation can be increased to a large extent by the use of a high speed centrifuge known as ultracentrifuge.

When a beam of light is passed through a true solution the path of the beam through the solution is not visible. But if the light is passed through a sol, its path becomes visible. This phenomenon is known as the Tyndall effect after the name of its discoverer. 

Colloidal particles in most dispersions move either towards the cathode or the anode when an electric field is applied to the dispersion. This movement of colloidal particles under an applied electrical field is called electrophoreses; this forms the basis of electrodeposition of colloids. Based on this principle, a very important process is used in the technique of DNA- fingerprinting what we call as ‘Gel-electrophoreses’ in which the DNA fragments that act as colloidal particles of different sizes & lengths are segregated out under the influence of an electric field. Rubber gloves and other intricate rubber articles are made by electroplating moulds with rubber from rubber sol. Colloids in sewage water are also removed by electroplating method. Colloidal ash particles in chimney gases are removed by passing them between high voltage plates.

Importance of Colloids & Everyday Physics: The synthetic fibers, plastics and rubbers are composed of molecules in the colloidal range as are also the molecules of proteins, starch and cellulose. One of the oldest, colloidal systems is the topsoil of the earth. Protoplasm is also a well known colloidal system.

In recent years a new field of study of particles in the range of size of colloidal particles has been developed. It is the study of gases, chromosomes, proteins and viruses. The methods and techniques of studying colloidal particles are now being applied to those particles in the filed of biochemistry…