My Science School

  There are 3 major reasons for a four-stroke engine of a two-wheeler being more eco-friendly than a two-stroke engine: In a two stroke engine, a part of the incoming air and fuel is short-circuited directly through the exhaust port of the cylinder and is carried away with the exhaust gases. This pollutes the atmosphere. But, the design of four-stroke engine is different there are valves (inlet and exhaust).

            Scavenging is effectively done in a four-stroke engine than in a two-stroke. (‘Scavenging’ is a process of removal of burnt gases from the engine cylinder.)

            If scavenging is not done properly, the residual burnt gas that inside the cylinder will be combusted again, this leads to smoky emission in two-stroke engines.

The lubrication system of a two-stroke engine is different from that of a four-stroke engine. In two-stroke engines, oil is mixed with the fuel (to provide lubrication for moving surfaces such as piston skirt and roller bearings). It is subsequently carried into the combustion chamber by the air stream, where it is partially burnt and partially pushed through the exhaust port, along with the exhaust gases. This results in smoky emission.

The suction, compression, expansion and exhaust strokes takes place in four strokes of the piston or two revolution of the crank shaft, in a four stroke engine

 In a two stroke engine compression and suction takes place in one stroke of piston and expansion and exhaust strokes also takes place in one stroke of piston. Hence in two strokes of piston all the four processes are completed which makes scavenging less efficient.

Scavenging is the process in which the products of combustion (i.e. burnt exhaust gases) are cleared from the cylinder and filling it with more or less completely with a fresh mixture of air and fuel. The incoming fresh mixture entering into the engine cylinder at certain velocity sweeps out the products of combustion from the cylinder.

 The fresh mixture entering acts as a scavenging or sweeping agent. But instead of acting as a sweeping agent, the fresh mixture also escapes through the exhaust port, as unburn hydrocarbons which are a pollutant.    

Most of the heavy vehicles are fitted with diesel engines, which generate more vibrations and noise than petrol engines.

When the engine is placed in the front it gives rise vibrations from the engine and the transmission line. It also causes discomfort to the passengers especially in case of long journeys.

If the engine is fitted at the rear it is comfortable to the passengers but problems such as remote operation of accelerator, gear shifting and inferior engine cooling arises. 

Rear engines reduce fatigue of the driver. He is also free from noise and vibration from the engine. Moreover, the weight on the front portion of the vehicle is reduced and so the torque needed to steer the vehicle would be less. Also, the hot air from the engine does not enter inside the cabin. However, the cost of manufacturing a rear engine vehicle is higher compared to front engine vehicle.

Fitting engines at the rear side has many advantages. First, the weight of the driving wheels (rear) is increased in slopes. This gives better traction through improved road adhesion.

 As the propeller shaft is absent, chassis height can be decreased. Further, the front portion of the vehicle is amenable to better designing and front axle construction can be simplified. But this type has certain disadvantages. They are difficult to service, have decreased cooling efficiency and are unstable at high speeds.

            In India, only front engine with front axle drive or rear axle drive is preferred as they give considerable ground clearance which is suitable for the road conditions.

The active ingredient in any mosquito repeller (whether it is mats, coils or solution) is d-trans allethrin or allethrin a.i (house hold insecticide). In the case of mats, apart from the main ingredient, the following are present – stabilizer (piperonyl butoxide), dye (blue), perfume, solvents (isopropyl myristate, butyl stearate) plus an inert ingredient like paper.

            Although mats and other repellants are not directly harmful to humans, symptoms of poisoning such as nervousness and anxiety may be experienced because of its active ingredients. Anyhow, on the basis of observations made from the use, experience and studies, no such symptoms have been acknowledged.

             If ingested, vomiting should be induced with care to prevent aspiration. If skin is contaminated, wash immediately with soap and water. If eyes are affected, wash them immediately with copious amounts of water. There is specific antidote for the chemical compound.

   When dry wood pieces and seeds of certain tree species are put in water, they absorb water and swell noticeably. This phenomenon of water absorption is called imbibitions.

            Imbibition is due to the presence of large number of hydrophilic colloids in both the living and dead cells of wooden materials. They include proteins and carbohydrates such as starch, cellulose and pectin. In the case of dry wood, there are more dead cells with lignified walls. As a result it readily absorbs and releases water depending on the environmental conditions.

            For example, during rains, relative humidity of atmospheric air is high. Hence, wooden doors absorb water molecules and swell. If the clearance between the door frame and door is insufficient to accommodate the swell, we experience difficulty in closing and opening it.

            Periodic painting helps to reduce moisture absorption and the difficulty.

     Physiologically, alimentary canal (gastrointestinal tract) is lined with mucous layer. Mucous contains mucin protein and water. Mucous is secreted by mucous glands present on the epithelium. Mucous, is present not only inside the alimentary canal, but also lines the respiratory and urinogenital tracts. This mucous lining primarily acts as a protective barrier and protects the underlying living cells from pathogens and from other physical and chemical hazards.

            When we drink very hot liquid this mucous lining protects the living cells beneath it from getting burnt. This happens mainly due to liquid water molecules in mucous. Water molecules have high enthalpy (E) and boiling point. This property of water molecules in mucous enables it to act as a heat absorbent and prevent the penetration of heat beneath it. Our skin is also involved in protection of underlying tissues and organs from external environmental hazards.

            Skin is composed of a superficial layer (the epidermis) and a deeper layer (the dermis). Dermis consists of many cell layers and most of the layers are made up of satiated, denucleated, keratinized dead cells. These layers act as physical barriers against the invasion of pathogens and harmful substances.

            But these stratified layers are not as effective as the mucous in the heat production mechanism. Because, these layers are dry in nature and contain no water molecules to absorb heat, and are permeable, when hot substances are poured on the skin, the dry horny layers manage to give little protection to the living cells from the heat.

    The liquid that leaves the body is almost unrelated, in chemical composition, to the liquid consumed. Any substance, solid or liquid, that goes down the esophagus, passes through the digestive tract and, if not absorbed, is incorporated into the faecal matter. Urine, in contrast, is created by the kidneys from metabolic waste produced in the tissues and transported through the bloodstream. Any coloured compound that one drinks either will or will not interact biochemically with the body’s system. If it does, this interaction (like any other chemical reaction it might undergo) will tend to alter or eliminate its colour. If it does not, the digestive system will usually decline to absorb it and will be excerted in the faeces which, you will have noticed, show considerable colour variation than the urine.

            Coloured substances in food and drink are usually organic compounds that the human body has an amazing ability to metabolize, turning them into colourless carbon dioxide, water and urea.

            The toughest stuff is often taken care of by the liver, which is a veritable waste incinerator. However, on the very infrequent occasion when the intake of coloured substances exceeds what the body can quickly metabolize, the colour is not necessarily removed as the liquid leaves the body. This is well known to anyone who has indulged in large quantities of borsch, or the Russian beetroot soup.

 

     While being made, the cereals are cooked into dry, crispy froths of syrupy, starchy stuff. In the process, and on cooling, they harden, and stresses induced during drying distort them. If you let them slowly absorb humidity from the air, they soften and the stresses relax gently, evenly and quietly. The cereals go leathery and sullen, and pass gently into milk and stomach.

            However, if you wet the fresh, crisp cereals their stresses are relieved suddenly and unevenly and thousands of minute shells suddenly find themselves with one side hard and stressed and the other side soft. They are bite.

            The processing of cereals for some breakfast foods creates bubbles in what is a brittle but weak material which swells when it absorbs water. As liquid touches one side of the bubble it swells and distorts so that the opposite side splits.

            The sound of this splitting is amplified by the air cavity in the same way as a stringed musical instrument vibration is amplified by its sound box.

 

Most of the beverages contain alkaloids which act as mild stimulants. Caffeine, for example, is found in coffee, tea, cocoa, milk chocolate and also in cola drinks. Tea has a trace of theophylline. Cocaine is found in products. These alkaloids are collectively referred to as methyl xanthenes. They share a number of pharmacological actions of much therapeutic interest: they relax, smoothen the muscles (notably bronchial muscle), and stimulate the central nervous system and cardiac muscle. They induce the kidneys to excrete more urine, stimulate mental activity, and quicken the reflexes, increase vigilance and decrease motor reactions time in response to both visual and auditory stimuli. They increase stamina and reduce fatigue. They give the users a feeling of confidence and power. They even induce euphoria in some users. These stimulant effects are short lived: they last for about an hour. They are then subsequently followed by depression. Overdose or repeated use may lead to paranoia, psychosis.

Alcohol generally refers to drinks which contain varying amounts of absolute alcohol (chemically termed ethyl alcohol). Alcoholic beverages are usually made by fermentation of sugars and carbohydrates (from different sources). Yeast is used to convert these into ethyl alcohol and carbon dioxide. As a food substance, alcoholic drinks have a restricted food value in the form of sugar (as in sweet wine) and carbohydrates (in beer). About 190-240 grams of pure alcohol per day is equivalent to 1300-1600 calories which is enough to provide basic energy for the body for a day. Inspite of its high calorific value it is better known as ‘empty calories’ because it does not provide the essential nutrients to the body. In addition, alcohol impairs absorption and metabolism of essential nutrients from other foods. ‘Alcoholics’ usually suffer from such deficiencies. This can be reduced by the type and manner of alcoholic beverage consumption.

Red meat is red because the muscle fibres which make up the bulk of the meat contain a high content of myoglobin and mitochondria, which are coloured red. Myoglobin, a protein similar to haemoglobin in red blood cells, acts as a store for oxygen within the muscle fibres.

            Mitochondria are organelles within cells which use oxygen to manufacture the compound ATP which supplies the energy for muscle contraction.

            The muscle fibres of white meat, by contrast, have a low content of myoglobin and mitochondria. The difference in colour between the fleshes of various animals is determined by the relative proportions of these two basic muscle fibre types. The fibres in red muscle fatigue slowly, whereas the fibres in white muscle fatigue rapidly.

            An active, fast swimming fish such as a tuna has a high proportion of fatigue-resistant red muscle in its flesh, whereas a much less active fish such as the plaise has mostly white muscle.

The colour of meat is governed by the concentration of myoglobin in the muscle tissue which produces the brown colouring during cooking.

 Chickens and turkeys are always assumed to have white meat, but free-range meat from these species (especially from the legs) is brown. This is because birds reared in the open exercise and become fitter than poultry grown in cages. The fitter the bird, the greater the ease of muscular respiration, and hence increased myoglobin levels in the muscle tissue, making the meat browner. All beef is brown because cattle are allowed to run around in fields, but pork is whiter because pigs are lazy. 

 

High-strength ceramics such as silicon nitride, dual hardness steel and layers of heavy nylon fabric make a bullet-proof glass impervious to bullets. The hard ceramic stops the bullet abruptly, dissipates its energy as it destroys the first layers of the glass at the point of impact and entangles it in as coarse mesh.

A textile bullet-proof vest is fashioned of 16-24 layers of nylon cloth of heavy weave, the layers stitched together like a quiet. Such vests or full-torso protectors can be worn undetected under regular clothing. A vest of 16 layers will stop regular handgun and submachine-gun bullets, those of 24 layers will stop the move powerful magnum bullets from the same weapons. 

Shattering of panes can be explained using the well-known principle of resonance. We have seen window panes vibrate when heavy vehicles such as a lorry pass by.

Likewise the panes of houses near airports also vibrate when aircraft fly nearby. In these cases, the noise (a mixture of sound waves of varying frequencies) generated by the vehicle sets up vibrations in the atmospheric air surrounding it. These vibrations (sound waves) transfer the energy from the source (vehicle) to the surrounding and dissipate it. If the noise is not intense, the sound dies away with in a short distance.

If it is intense, the waves travel long distances. When these waves come across solid objects such as window panes, they transfer their energy to the object and force them to vibrate.

 If the frequency of the sound wave matches with the natural frequency (Any object will have a natural frequency of vibration which depends on the nature of the material) of the object, resonance sets in the object begins to absorb the incident energy and forced to vibrate with large amplitudes. In case of window panes, its edges are held (if not tightly) by the window frame which prevent the oscillation. This results in shattering. 

The bristles of a shaving brush are bunched together to ensure that there are a large number of thin columns of air in-between them. When the brush is moved to and fro, the soap solution seeps into the brush, due to surface tension, partially filling the air columns.

 While shaving, the soap solution stuck to the skin is dragged to form thin films. But when stretched beyond a certain length, limited by surface tension, the films break and in that process trap a little bit of air to form small bubbles. As there are hundreds of bristles involved in the bubble making process, we get lather within a short time.

 The same principle applies to tooth brush and the brushes used for washing.

 

Honey is a very dry product, mostly sugar. Any water that comes into contact with it will be drawn in by osmosis. As a result, most bacteria are dehydrated, killing them or rendering them weak and fragile.

 Bees also treat the honey with an enzyme that generates free radicals, in effect sterilizing the honey with hydrogen peroxide.

In ancient times, honey was sometimes used as a wound dressing, and some modern doctors still use sugar. Experts say the treatment probably works because sugar dries the bed of the wound to promote new tissue growth and dehydrates the bacteria that cause infection.

There are commercial wound pastes made of synthetic microscopic water-absorbing, bends that do the something. 

Honey is adulterated by way of adding jiggery syrup. To verify whether honey is pure, take a glass of water and pour one tablespoon of honey in it. Gently shake the glass (note not to stir). If the honey completely dissolves in water it is adulterated, On the other hand if it stays as a mass, it is pure honey. 

Generally a substance dissolved in a liquid lowers the freezing point or melting point of that liquid. When salt is added to ice at room temperature, some of the ice melts and cools the salt to zero degrees Celsius. The salt solution produced cannot remain in equilibrium with ice at zero degrees. It is possible only when the ice is at the freezing point of the solution (less than 0 degrees Celsius). So more ice in contact with the salt solutions melts taking the necessary latent heat of fusion from the salt solution, whose temperature is consequently lowered.

More salt thus dissolves, keeping the solution saturated and the process continues till the temperature of the solution reduced to -21 degrees Centigrade. Only at this point (eutectic point) ice is in equilibrium with saturated salt solution. When 23 per cent of salt is added to ice, the freezing point is lowered to -21 degrees.      

         

Solid ice exists at zero degrees Celsius and salt at room temperature which is bound to be higher. So, when the two mix, ice begins to melt. But the temperature still remains at zero. A little of the salt dissolves in the water thus formed. In this process, the fine, solid particles of salt breaks down to positive sodium ions and negative chloride ions (dissociation). This change requires energy which is absorbed from the solution which is cooled below zero degrees Celsius. As more and more salt dissolves, temperature goes down further till -21 degrees Celsius is reached. At this stage, the solution is saturated, that is, the maximum solubility of salt at that temperature has been attained. Ice, solution and salt co-exist at this point called eutectic point.

This principle is used in making freezing mixtures which provide sub-zero temperatures. If calcium chloride is employed instead of sodium chloride, temperatures as low as -55 degrees Celsius could be obtained.

 Another application of salt and ice is in de-icing of roads during winter. The smooth, slippery surface of ice is dangerous to fast moving vehicles. When salt is thrown on the ice, it dissolves and the solution though at a low temperature flows away leaving the roads free. Because of the presence of about 3 percent of salts (chiefly common salt) sea water freezes at -2 degrees Celsius instead of at zero.

   

Salt is used to melt ice on roads and sidewalks. On contact with ice, some of the salt dissolves.

The salt solution has a lower freezing point than pure ice and exists as a liquid at zero degrees Celsius. So even on a cold day, the ice can be melted drained using salt.

One can use sodium chloride (common salt) and calcium chloride for the above purpose. The depression of the freezing point depends on the number of particles in a given amount of solvent.

Electrolytes are compounds which produce ions in solution. NaCI exists as a sodium ion and a chloride ion in solution and calcium chloride as a calcium ion and two chloride ions. Among these the calcium salt is better clearing ice from sidewalks as it produces more particles (three ions – one calcium ion and two chloride ions) in the solution. But we cannot use them for cleaning ice in automobile radiators because of their corrosive nature. For that ethylene glycol is used as antifreeze even though it is not as efficient as the calcium salt.