My Science School

Obviously because of the string and the tail. How the string is tied to the sheet of paper (at certain angles) plays an important role in the successful flight of the kite. First, the sheet of paper is made stiff using thin sticks so that it does not bend due to the forces of the wind. Next, 3-4 small strings of equal length are attached. All this is to make the kite fly at an angle with the direction of the wind.

According to the laws of physics, any force acting on can be separated into two components – one horizontal and the other vertical. Generally the vertical component lifts the object (against gravity) and the horizontal component pushes the object (along the direction of the force). Here the force acting on the kite is due to the wind.

 In the case of pieces of paper, the wind force blows them away as they are not secured anywhere. But in the case of the kite, it is held by the string in on e direction (a restoring force) and the wind is exerting its force in the opposite direction.

 The net force on the kite is resolved into the horizontal and vertical components mentioned above. These force components depend on the angle of the kite’s axis to the wind direction. When the lifting force is sufficient enough, the kite begins to fly. 

 At times we pull the string or run into the wind. These are tricks to increase the lifting force and make the kite fly higher. Some kites tend to rotate along the axis of the string. To prevent this rotation, a long tail is attached.

 The flight of the kite may look simple going by the above explanation. But there is a lot more to it: For example, if we closely watch the flying kite we can see that it is very dynamic. It adjusts its position continuously depending on the movement of the air surrounding it. All this it does, may be because it wants to fly! 

            In most cases dirt adheres to the fibres of textile fabrics by 2 kinds of forces – first by sticking to a coating of grease or a dried coating of substances which swell up in water or other solvents (starch, Proteins and other glue like substances); second by direct adhesion because of the physico – chemical character of the fibres and the dirt. Dirt consists of fatty substances, proteins, and dust and soot particles. Such dirt is largely insoluble in water or is water repellent. Used shirt is soiled with greasy substances constituting about 0.25 percent of its weight; collar may contain as much as 1.2 percent of its weight of greasy dirt.

The dirt may be held by the fibres in various ways; mechanically (pigments are jammed between fibres), chemically (fruit oil or ink strains) by absorption (feebler chemical band, dissoluble by detergents) and by electric forces. As most of the dirt is firmly held by the fibres, pure water is not very effective. Chemical cleaning or dry cleaning uses liquids other than water for cleaning of fabrics. In this treatment adhering dirt of the first kind is removed by dissolving the grease or their sticky matter to which the dirt particles are clinging.

A wide range of solvents are employed: carbon tetrachloride, trichloroethylene, tetrachloro ethylene, naphtha (petroleum ether) and benzene. A modern dry cleaning plant comprises a number of specialized machines and appliances. The soiled garments are treated with the solvents in rotating drums.

Contaminated solvent is drained off and purified for re-use. Cleaned garments are dried, impregnated and reshaped. In some cases, however, it is necessary to use water as an additional solvent or swelling agent.

The second type of dirt is dislodged from the fabric by means of detergents added to water. After this wet treatment the fabric is usually treated in weak acid solutions (to revive colours). Rinsed, centrifuged and dried.

Impregnation treatment may be applied at an intermediate stage to stiffen the fabric and make it water- and dirt-repellent. Garments are finally pressed on special machines operated with steam and air. 

      Fabrics such as cotton and linen are treated with thermosetting resins such as urea formaldehyde and melamine formaldehyde to get a durable finish, writes Mr. Surya Kumar of Tuticorin.

A thermosetting resin is a plastic that Solidifies when heated under pressure. They improve the capacity of the fabrics to resist and recover from creases formed during wear. According to him, only when clothes are pressed by a heated iron, under slight pressure, the resins develop cross linked chains between them which give stiffness to the clothes. A cold iron will not be able to do that.

Dr. J. Venkat Rao, Head of the Department of Textile Technology, Anna University, Madras, says  that  this explanation holds good only for certain fabrics. There are a few other factors which are to be considered for ironing clothes, he says.

The first is moistening the cloth. The water makes fabrics such as wool or silk to swell whereas it imparts plasticity to polyester. This allows the fabric to set in any predetermined pattern when pressed with a hot iron box. Because of the heat the moisture evaporates and the cloth sets neatly (as it is made mouldable) as the creases are removed.

According to Dr. Rao, different kinds of clothes are capable of withstanding varying quantities of heat. Natural fabrics such as cotton and linen are not thermoplastic by nature and hence are capable of withstanding high temperature. Synthetic fabrics such as nylon and polyester are thermoplastic. They melt at even slightly high temperatures and hence too much heat should not be applied to these fabrics. Another factor that controls ironing is the pressure applied – heavier iron boxes can exe greater pressure. This explains why dhobi’s ironing is far better than the housewife’s.

A soft bed above a hard surface perhaps helps in distributing the pressure evenly on the cloth.

 

Left-handedness is due to asymmetry of the brain. It is not a disorder and is more common in males than in females. Actually, in the foetus, the left and right hemispheres of the brain are symmetrical.

Only after about six months of its birth, babies show a preference for either the right or left side of the body. This is due to functional asymmetry of two sides of the brain. It is said that the left hemisphere of the brain controls the right side of the rest of the body and vice versa.

As a result, it seems the left hemisphere is more active than the right, in a majority of the population. Though this theory is not accepted by neurologists in humans it has been proved in the case of dolphins.

Due to lack of symmetry in the brain, in 90 per cent of the population, the right leg, right arm and muscles on the right side are slightly larger and heavier than those on the left. It is almost the reverse in the rest of the population.

Left handedness is generally associated with special talents and also with certain disorders such as stuttering, dyslexia, depression and emotional withdrawal.                                                                                                                                                                          

Nearly 75 per cent of the population is strongly right- handed and about 90 per cent is predominantly right-handed. Among the rest, a great deal of variability exists. Some are strongly left-handed, and others, called ambidextrous, are left-handed for some activities and right-handed for others.

            Handedness is defined as a preference for the use of either the right hand or the left hand. Although most animals have a preferred paw or hand, only people have a species-typical preference for the right hand. Researchers suggest that differences in left and right-handers in patterns of brain organization may be associated with differences in skills, aptitudes, and perhaps even personalities. In the large majority of right-handers (98 or 99 per cent), speech is controlled by the left side of the brain.

The right hemisphere of the brain is usually specialized for recognizing and remembering faces and understanding spatial relationships.  In left-handers, the brain organization is unpredictable. In about 70 per cent of the left-handers speech is controlled by the left hemisphere of the brain, as is the case for right-handers, but in the remaining left-handers speech is controlled by the right hemisphere.  In some left-handers, both the hemispheres are capable of controlling, speech.

The hand an individual comes to prefer is determined, in part, genetically, but this does not mean, for example, that two right-handed parents cannot have a left-handed child, or the reverse.

The precise mechanisms by which genes affect handedness are still unknown. A physical injury may also be involved.

During the birth process, the region of the brain controlling the hand is sometimes damaged, so that a child who would have been right-handed without such damage becomes left-handed.

 Social pressures have had a considerable effect on handedness. Using the left hand to pass on or receive something from others is strongly discouraged even now in many countries including India.

Only in recent years has society become tolerant of differences among people to accept left-handedness as a benign trait.

 Many famous persons, including Leonardo da Vinci, Benjamin Franklin, and Lewis Carroll, were left-handed.

Clouds are made of water droplets and dust in the atmosphere at altitudes of 1 to 16 km. While travelling through air, due to friction, the water droplets get electrically charged.

 Lightning occurs due to sparking between oppositely charged clouds - a high voltage spark rushes towards the ground (at zero potential) through moisture-filled air.

If any around based structure is on the path of the spark, the top of that structure is excited to a high electrical potential while its bottom (in contact with the around) remains at zero voltage. This high potential difference sets a very high current in the structure causing sudden heat generation in the material and destruction. But in flying aero-planes, there is nothing like a ground point which remains always at zero voltage.

Hence even if hit a lightning, the plane's entire surface acquires the same high potential and due to lack of potential difference there is no current and hence no destruction.

           The mechanism of seeing in the dark involves two types of cells – rods and cones, in the eye. These cells are present in the light – sensitive innermost layer of the eye called the retina. They lie in front of a pigmented tissue layer. Cones are present in the area of greatest visual activity – fovea contrails, which lies at the centre of small yellow pigment spot behind the pupil. Rods and cones are present around the fovea.

            Cones are active under intense illumination, whereas rods are active in dim light. In the dark rods are sensitized by a pigment called Rhodospin or the visual purple that is formed within the rods. Rhodospin is bleaches by light and is reformed by the rods in darkness. Hence a person who steps from sunlight into a dark room experiences a blinding feeling till the pigments begin to form. This process takes around 30 minutes to reach maximum sensitivity.

            On completion the eyes become sensitive to low levels of illumination and are said to be dark-adapted. Meanwhile the cones adapt themselves to fainter light in the ambience of low intensity illumination, which may take around five minutes.

            The best example is finding our way to our seats in a movie theatre after the show begins. Initially there is a blinding feeling when we do not see anything. But later the cones in the retina get adapted to the light from the film screen, when we are able to find the seats; this is followed by adaption of the rods which enables us to see everyone around us.

          Mummies are embalmed bodies that have been preserved for thousands of years. The dead have been mummified with the help of good drying agents applied all over the body.

            Drying agents and other materials were stuffed inside the body to maintain its shape after removing the internal organs. The word mummy is derived from the Persian word mummia meaning bitumen because the black resin used for embalming the dead looked like bitumen.

            Three techniques of mummification have been discovered by Greek historians. The methodology was the same in all the three cases and the differences lie in the process of extraction of internal organs. Mummies belonging to 1570-1070 BC are still found to be in good condition.

            Actually in the process of mummification embalmers removed all the internal organs except the heart and kidneys. The brain was removed through the nostril using a hook. They soaked them in natron (a mixture of salt, sodium bi-carbonate and sodium carbonate). It was then bandaged and kept in jars. The internal cavities were stuffed with lines bags of sawdust, natron bags, and resin coated material.

            The nostrils and eyes were stuffed with linen rolls. Cedar oil, natron and purgatives were then smeared on the body to close the pores. After this, the body was wrapped in long sheets of fine line. Toes, fingers and limbs were separately wrapped and then the torso was wrapped up in several layers.

            A mask revealing the external features, made of pliable linen treated with resin was fixed on the face. According to ancient texts a complete treatment could take about 70 days. Though resin has burnt the skin of the dead body in many cases the hairs were seen to be intact.

            Human skin is made of four layers – the topmost layer is stratum cornium, followed by epidermis and sub-cutaneous layers. When mehndhi is applied on the skin, the red pigments present in it are transported along with water through the small pores in the stratum cornium. These pigments get trapped between the stratum cornium and epidermis. As the hand dries, the water evaporates leaving the pigments which impart the colour.

            In the case of the nail, the pigments are trapped between the horny plate-like cells which are piled in lamellar layers. The pores in the skin are larger than those in the nail. This actually accounts for the rapid fading of the colour in the skin compared to that of the nail.

  Any object will be stable in its position if the line drawn perpendicular to the ground from the object’s centre of gravity falls within its base.

            While walking on a rope, as the base is very thin (as thin as the rope), to be stable the artist has to move his centre of gravity appropriately. This he does by holding a bamboo pole horizontally or using an umbrella or just by spreading his hands.

            When the artist feels that he is falling to his left, he moves the pole to his right (and the vice versa) and counters the forces disturbing his balance and makes the centre of gravity fall within his base.

            Now one may ask, how does one sense these forces and maintain balance? This is achieved only by practice.

            According to the theory of rhythm perception, the perception of rhythm involves the motor system just as much as the sensory system. It postulates that a ‘beat’ is actually perceived as a movement.

            The theory then suggests that because a beat is perceived as a movement, the activation of a stereotyped behaviour such as tapping your foot in time with the beat is a natural extension of the way motor and sensory systems often work together to produce a percept.

 

 

A pencil mark actually consists of graphite particles abraded from the pencil point by the paper. These particles, which have an angular, gritty look under the microscope, are for an HB lead pencil, typically between 2 and 10 micrometers in diameter. The particles lie slightly below the surface of the paper, interlocked between its fibres.

            A signal rub using a rubber sufficiently soft to reach between the fibres will pick up most of them. Inspection of the rubber shows the undamaged particles adhering to the surface.

            An effective erasing material is also abraded by the paper surface, producing the familiar small spindles of rubber or eraser material, which wrap up the graphite particles. At 200 x magnification, these look like roly-poly puddings studded with graphite raisins.

   Parboiling involves soaking paddy in water for a short time followed by heating once or twice in steam and drying before milling. Dehusking of parboiled rice is easy and the grain becomes tougher resulting in reduced losses during milling.

            The nutritive value of rice increases after parboiling, because the water dissolves the vitamins and minerals present in the hull and brancoat carries them into the endosperm. So the loss of vitamin B1, riboflavin and niacin due to milling and polishing is comparatively low in the parboiled rice than raw rice. Parboiled rice will not turn into glutinous mass when cooked. Baking of leavened dough of wheat helps to make bread. Baking is done in an oven preheated to 204 degrees C. During the first 10-12 minutes of baking there is an increase in dough volume. This is called oven spring. This is caused by an expansion of gases owing to the high temperature of the oven and due to increased enzyme activity in the centre of the dough. As baking continues, gluten a constituent of wheat dough expands without breaking and finally forms a rigid structure due to coagulation.

            This helps in the retention to the rapidly expanding gases. Excess gases, CO2, alcohol and water vapour help to gelatinize the starch and structure is established. This aerated and finely vesicated crumb is very helpful for easy mastication of bread.

            Using heat to bring about desirable changes in foods is called cooking. Cooking improves flavour and appearance and makes the food more palatable and digestible. Legumes and cereal grains contain trypsin inhibitors and other toxic substances which affect the digestibility and availability of sulphur containing amino acids.

            Cooking destroys these toxic proteins and favours easy digestion Starch molecules which are the main source of calories in many diets when in an aqueous or moist environment swell and rupture and this permits greater enzymatic digestion by enzymes like amylase. Cooking thus increases the digestibility of carbohydrates.

         We can’t fry food with water because its boiling point is lower than that of oil. Generally all food materials contain water in an occluded from or as water of hydration.

    We fry food essentially to remove this water. For this, the food needs to be heated beyond the boiling point of water (100 degrees C). If we use water as the frying medium, the water from the food cannot be removed as the medium itself gets vapourized.

                                                                                     However, oil can be heated to more than      without                                                                                        charring the food. Being nonvolatile at this                                                                                                        temperature, heat from the oil facilities frying. 

Fuel has to be heated to a minimum temperature, know as kindling temperature or ignition temperature for a successful and continuous burning.  We largely depend upon match sticks for creating fire. It contains combustible W (oxidisable) substance and an oxidizing (oxygen supplying) agent. We supply heat energy by rubbing the head against rough surface. Every fuel has to mix up with oxygen present in air to form a mixture of right composition for successful combustion.

The composition of the mixture can be between two limits namely lower and upper limits. Those limits are called limits of inflammability or explosive range. We should know that even when the temperature maintained is equal to kindling temperature, we cannot produce fire with fuel only or with oxygen only.

Kindling temperature depends upon the chemical nature and explosive range depends upon the volatile (vapour forming) nature of the fuel. Those two properties do not have any direct relation with size or shape of the fuel. But, of course, it seems that powdered fuel, say saw-dust in case of wood catches fire quickly rather than large log.

This difference in size or shape affects neither the kindling temperature nor the volatile nature of the fuel. The rapidity in catching fire is due to different reasons. In case of powdered fuel, small fuel particle is introduced into a large flame. That means supply of activation energy in the form of heat is very fast. In this case, availability of oxygen will also be a very high. Hence the quick ignition. But in case of logs, large mass is heated by relatively small flame. That means supply of activation energy in the form of heat is very slow.

Also, a large portion of the heat supplied to the log will be dissipated to other parts due to conduction. Chance for loss of heat energy to the surrounding cannot be also neglected. This will further slow down the process of attainment of ignition temperature.

Even when the whole log attains the ignition temperature, only the particles present on the surface can form explosive mixture combining the oxygen present, in air. Hence the delayed ignition. 

Ignition temperature is specific to a substance. It is temperature at which the substance starts burning. A piece of wood catches fire quickly attain the fire point quickly. But in case of a large log when you apply flame a point of edge, the temperature transfer takes of big log a long time. 

Fuel has to be heated to a minimum temperature, know as kindling temperature or ignition temperature for a successful and continuous burning.  We largely depend upon match sticks for creating fire. It contains combustible W (oxidisable) substance and an oxidizing (oxygen supplying) agent. We supply heat energy by rubbing the head against rough surface. Every fuel has to mix up with oxygen present in air to form a mixture of right composition for successful combustion.

The composition of the mixture can be between two limits namely lower and upper limits. Those limits are called limits of inflammability or explosive range. We should know that even when the temperature maintained is equal to kindling temperature, we cannot produce fire with fuel only or with oxygen only.

Kindling temperature depends upon the chemical nature and explosive range depends upon the volatile (vapour forming) nature of the fuel. Those two properties do not have any direct relation with size or shape of the fuel. But, of course, it seems that powdered fuel, say saw-dust in case of wood catches fire quickly rather than large log.

This difference in size or shape affects neither the kindling temperature nor the volatile nature of the fuel. The rapidity in catching fire is due to different reasons. In case of powdered fuel, small fuel particle is introduced into a large flame. That means supply of activation energy in the form of heat is very fast. In this case, availability of oxygen will also be a very high. Hence the quick ignition. But in case of logs, large mass is heated by relatively small flame. That means supply of activation energy in the form of heat is very slow.

Also, a large portion of the heat supplied to the log will be dissipated to other parts due to conduction. Chance for loss of heat energy to the surrounding cannot be also neglected. This will further slow down the process of attainment of ignition temperature.

Even when the whole log attains the ignition temperature, only the particles present on the surface can form explosive mixture combining the oxygen present, in air. Hence the delayed ignition. 

Ignition temperature is specific to a substance. It is temperature at which the substance starts burning. A piece of wood catches fire quickly attain the fire point quickly. But in case of a large log when you apply flame a point of edge, the temperature transfer takes of big log a long time.