My Science School

            The seconds hand of both quartz and spring watches move in jerks. Only the movement is much more discernible in quartz watches. In spring watches the movement of the seconds hand is guided by the oscillations of the balance-wheel driven by the hair spring. Since the balance wheel oscillates several times a second, the seconds hand in a spring watch appears to move smoothly as the small jerks are almost non-discernible. On the other hand, in quartz watches, the battery powers a stepping motor that moves the second hand in a single step once every second, which can be quite easily made out and the movement appears jerky.

        Another reason for the illusion is the difference in the amount of angular movement each jerk produces in a second hand. In spring watches it is only  whereas in quartz watches it moves by as much as  in a single step.

                                     

   Soaps are salts of fatty acids. Common soaps are water soluble sodium and potassium salts of fatty acids. Soap cannot form lather unless it dissolves in water. Hard water does not dissolve soap because the calcium and magnesium salts present in it produce insoluble substances by reacting with soap. These insoluble substances separate out as scum and reduce the effectiveness of the soap as a cleansing agent.

 Synthetic fibres are made artificially. They are solid, smooth and straight in structure unlike a natural fibre like cotton which is hollow. So when synthetic fabrics are soaked in water, only the surface of the fibres gets wet as water does not enter the body of the fibre. That is why these fabrics absorb very little amount of water and dry quickly as the water drips away. Such fabrics are also known as ‘drip dry’.

            About three-fourths of a poultry egg is plain water in which the albumin protein and fats are suspended. At room temperature, the protein strands are tightly folded in a complex three-dimensional shape. Because the individual proteins are able to move freely, both the egg-white and the yolk remain liquid. But when the egg is placed in boiling water, the protein strands begin to straighten out. The protein ends, normally protected within the folds, become exposed. When the temperature rises to , the open ends join together in bridge-like bonds forming a giant structure. These new bonds prevent the molecules to move                                                                                              thereby making the egg material solid.

            Fanning produces a sense of coolness in the body because of evaporation of moisture from the skin. On fanning the rate of evaporation increases. The water molecules from the body in the form of perspiration take up heat energy from the body and escape from the body surface, thus cooling it. However, if the air is hot, as in a desert, fanning does not produce any cooling as the heat for evaporation is supplied by the hot air.

   The intensity of light coming out from a TV screen is very high. If this bright light with varying intensity is the only source of light in a darkened room, the eye has to constantly adjust for vision by opening wide or narrowing the iris when a person focuses on the bright screen or looks away from it. The constant adjustments that the eye has to make causes eye strain. Whereas in a lighted room, intensity of the T.V. image is only a little brighter than the surroundings, which makes the viewing easier for the eyes. It is, therefore, advised to have some light in the room while watching the television.

                                    

            The softness of ice cream arises out of the nature of the ingredients and the way they are combined. Two essential ingredients of ice-cream are fat in the form of cream and air bubbles introduced by stirring.  As the water in the ingredients starts freezing, the suspended fat globules prevent the whole content from freezing as a single mass. Tiny air bubbles trapped in the mixture due to continuous stirring of the ingredients also prevent the ice crystals from growing as the temperature is reduced further. This prevents the ice cream from becoming hard and the frozen mass remains soft.

  In the case of ice, the absence of fat and air bubbles leads to the tiny ice crystals growing into large chunks of hard ice.

            There is a close link between the sense of taste and the sense of smell. Much of what we think of as taste has a big smell component. The taste buds in the tongue monitor relatively crude sensation of the four basic tastes – sweet, salty, sour and bitter. Faint vapours of whatever we eat drift into the nasal cavity where the smell receptors add more detail to the information given by the taste buds.

When we have a cold our nose becomes blocked and the sensation of smell ceases. The gas and vapours from the food cannot be sensed by the smell receptors; consequently we cannot perceive the smell or aroma of the food, which in turn makes the food appear tasteless.

            Tears produced by the tear glands keep the eyes moist and are normally drained off through the nose. Onions contain a number of water soluble volatile substances containing sulfur. On cutting the onion these substances quickly spread into the air and cause irritation in eyes. The tear glands start secreting more and more tears to wash out the irritants. The tears are produced so rapidly that they cannot be drained out through nose and so run down the eyes.

Potato is a living plant tuber (a modified stem specialized for storage of food). There is a lot of difference in the cellular structure and chemical nature of the potato peel and that of the flesh. The flesh is made up of parenchyma cells, specialized to store starch. The walls of these cells are made up of cellulose and they are joined together by a sort of glue called pectin. The peel or the skin of potato is made up of cork cells, the walls of which have a lot of lignin and suberin deposits. These substances give a greater mechanical and structural strength to the corky cells and hence are easy to remove as a continuous peel. In un-boiled potato the corky skin and the flesh of potato are sealed together by pectin. Hence peeling is difficult. During boiling, little change occurs in the corky peel, but the fleshy parenchyma becomes soft. Also the glue-like substances present between the cells, swell up and break down. As a result, the adhesion between the peel and the flesh is reduced and the effort required to separate the peel from the flesh is highly reduced. Hence it is easier to peel a boiled potato.

            All plants respond to touch, but Mimosa pudica, or the “touch-me-not” plant is more sensitive than the others. Whenever touched, the leaves of the mimosa plant close and drop immediately, appearing like a dead plant. Possibly it is a defense mechanism by which the plant protects itself against its enemies.

   The opening and closing of the leaflets and the entire leaf are controlled by fluid-filled sac-like structures found at the base of not only the compound leaf but of each leaflet as well. When the leaf is touched, a chemical signal immediately moves to the base of each leaflet making the fluid drain away from the sac which makes the leaflet fold. When the signal reaches the base of the whole leaf, it makes the entire leaf drop. If left untouched for some time, the sacs fill up and the leaflets open again.

            Lightning occurs when a massive electrical discharge takes place between two oppositely charged clouds or between a charged cloud and the ground. The charges develop in thunder clouds due to the friction of water droplets with air as the droplets move up and down with the rising and descending air currents within the cloud. During a bolt of lightning, thousands of amperes of electricity flows through the air in a fraction of a second. This rapidly heats up the air along its path which expands very fast producing shock waves which we hear as thunder. Although the lightning and thunder are produced at the same instant, we hear the thunder later because light travels faster than sound.

    The reason lies in the water cycle. The total quantity of water in the lakes, rivers and oceans of the world remains almost the same always; only the distribution changes periodically. The water cycle begins as the Sun evaporates water from oceans, lakes, rivers and soil. The vapour forms clouds which precipitate as rain or snow, 75 per cent of which falls on the oceans. The remainder falls on land. Some of this water seeps into the earth as groundwater while some is returned to the oceans by the rivers. Thus there is constant balance between water flowing into the oceans and water evaporating from them. That is why the oceans do not overflow.

            The Earth’s axis – the imaginary line around which the Earth turns daily is titled at an angle of  to the plane of its orbit. The seasons are caused by this tilt and by the fact that the Earth’s axis always holds the same orientation in space. As the Earth travels round the Sun, the North Pole is sometimes directed towards the Sun and sometimes directed away from it. When the North Pole is directed towards the Sun, sunray’s strike the northern hemisphere almost directly. This causes summer in the northern hemisphere and the southern hemisphere has winter. Three months later, the North Pole begins to slant away from the Sun. This causes the northern autumn and southern spring. After another three months the North Pole it tilted away from the Sun, this causes winter in the north and summer in the south. Finally the North Pole tilts towards the Sun again, bringing spring to north and autumn to south.

The main reason why some trees shed leaves is to conserve water during the winter months. When root activity and water absorption decrease, deciduous trees drop their leaves. This helps them keep water loss at the minimum. Unlike deciduous trees, which lose their leaves all at the same time, evergreen trees, mostly conifers, shed and replace leaves continuously. Before the leaves fall, triggered by changes in temperature and daylight, groups of the soft cells from around the base of the leaf stalk. These cells produce an enzyme which dissolves the stalk cell walls and causes leaf to detach. Discarding their leaves also helps trees dispose of toxic and waste products which accumulate in the leaves before they fall.