My Science School

            Stars are giant glowing balls of fire situated far away from us. Many of them are several times larger than our sun, but being very far away, appear as points of light. Stars themselves don’t twinkle but appear as steady points of light when seen from space where there is no atmosphere. The twinkling of stars as seen from ground is caused by the unsteadiness of the Earth’s atmosphere. When light from an extended source such as the Sun, Moon or the planets pass through the atmosphere, it does not appear to twinkle because the slight changes in apparent brightness in one part is usually compensated by light coming from another part of the celestial object. But when light from a point source like a distant star passes through the atmosphere the fluctuations in the light intensity is not                                                                                       compensated and the star appears to twinkle.

            According to the plate tectonics theory, the Earth’s surface consists of huge, rocky plates that move slowly past one another. Known as tectonic plates, some of these carry continents, others the ocean floors and some a combination of the two. Most earthquakes take place along the boundary between two plates. Propelled by heat-driven currents in the softer rock beneath them, the plates constantly pull apart, collide, or grind against each other. When the strain becomes too great, the pent-up energy ruptures the rocks and creates a fracture known as a fault. This sudden release of energy unleashes the ground-shaking vibrations that constitute an earthquake.

  The sky as seen from the Earth appears blue because of the scattering of sunlight by the Earth’s atmosphere. When sunlight reaches the Earth’s atmosphere, it hits suspended molecules of air and dust and gets scattered in all directions. Sunlight consists of light waves of varying wavelengths each of which is seen as a different colour. The size of the scattering molecules decides which colour is scattered most. Gas molecules in the atmosphere scatter blue colour the most. So during the day the sky appears blue because more blue light is deflected towards the earth. However, on the Moon, since there is no atmosphere, scattering of sunlight is negligible. So the sky appears black from the Moon.

  The tides are caused by the gravitational pull of the Moon on Earth’s oceans. In fact, the Moon’s gravitational pull attracts everything, even the land and mountains, though being rigid and fixed they do not move. But not so with the oceans. Being an unbroken stretch of water, spread over almost 70% of the Earth’s surface, the Moon’s pull can easily draw water away from one part and pile it up at another which show up as tides. However, this is not possible in a small body of water such as a lake. Here the total surface area and volume of water is too small to produce any perceptible change in the level as happens in tides.

                                    

When your mother frowns at you without saying a word, you know that you have displeased her. Her displeasure is expressed through her   body language. In this way, other emotions too, are reflected through When you cross your arms, and lean away from another person to you are telling him that you want him to keep a distance, though of course, it may also mean that your arms are cold. If you look at a person in the eyes while speaking, it is a sign of honesty and straight forwardness. Looking away can mean you are lying, or that you don’t like the person. A person who shakes his legs constantly, or wets his lips is under stress. A person who leans towards you with clenched fists is quite likely to attract you! So you see, understanding body language helps you to understand the emotions of other people better.

 

 

Some species of animals are especially clever at detecting human body language, both voluntary and involuntary. There is the instance of a horse called Hans, who seemed to be able to add, subtract, multiply, divide, work with fractions and do other intellectual tasks. If you asked him a question, Hans would reply by tapping his foot till the correct

Han’s abilities amazed the world, but a formal investigation showed that the horse was not really calculating the answers, but was responding to the questioner’s body language. As the horse’s taps approached the right answer, the questioner’s posture and facial expression

       

    Fog is a collection of tiny water droplets that float in the air near the ground. When there is a sudden fall in temperature, moisture present in the air condenses and begins to change into tiny droplets of water. The air holds these droplets as fog as long as the temperature remains low. But when the air temperature rises, the tiny droplets evaporate and the fog disappears.

                        

 

            Climate is the average weather condition of a place recorded over a long period. It depends mainly on the geographical location, but factors such as distance from the equator, proximity to the sea, altitude and topography influence climate of a given place. Places located near the equator are generally hotter than those located at higher latitudes. Places located at higher altitudes are usually cooler than the plains. Coastal areas generally have a more humid climate than places far inland.

            The waves are higher near beaches than in interior parts of the sea mainly because of the shallowness of the sea near beaches. The shape of the coast and surface features of the sea bottom near the coast also decide the height of the waves. In deep seas, the water in a wave moves in large vertical circles, without actually moving forward. Near the beaches such circulation is modified by the closeness of the bottom. This leads to increase in the height of the waves. Speed and direction of the wind, and the distance over which the wind is blowing are other factors that can further affect the height of waves. A                                                                                         strong wind can create huge waves even in mid sea.

            Rivers usually meander when they flow over the plains. On the plains, the gradient is usually low and river has no preferred direction of flow. Its course is usually determined by local irregularities in the terrain and soil condition. In such a situation when the river bends in one direction, it tends to scoop out its outer bank and deposit silt on the inner bend. After scouring one bank the water is deflected towards the opposite bank which now starts getting eroded. The process continues with the river changing direction over short distances, giving rise to the familiar meanders.

            Clouds are large masses of fine water droplets or ice particles formed by condensing water vapour. In spite of their great masses, clouds float in the sky because they are held up by the up drift caused by hot air rising from the ground below. Within the clouds themselves strong currents of upward rising air keep the droplets or ice crystals in constant motion which not only helps them keep afloat but also leads to the rapid changes in shapes of clouds.

            Ice skating is an act of gliding over the smooth surface of hard ice on ice skates – boots with attached metal blades. It is easy t skate on hard and smooth surface of ice because of the absence of frictional force between ice and the skating blade. Another reason is that ice melts under the pressure of the sharp blades of the skate and water thus formed acts as a lubricant which helps in skating. It is not possible to skate on snow or sand because the surface is not hard.

            The peculiar smell is produced by the soil inhabiting bacteria called streptomycetes. Streptomycetes are abundant in dry warm soil – a million of them are present in a pinch of soil. They release compounds such as geosmin and 2-methyl isoborneol, which vapourize easily, when wetted by rain water after a dry spell. That is why we get the musty odour only after the first rain of the rainy season. The smell can be detected in a newly ploughed field also.

            The bottom of lakes and ponds, which usually hold still water, is usually covered with sediments formed of clay material. Clay contains chemical substances such as sodium bentonite which have the property of expanding when wet. The loss of moisture, therefore, makes this layer of clay shrink resulting in cracks on its surface. Thus, in summers when lakes and ponds go dry, the surface of their beds shows large cracks.

            Vultures are scavenger birds which feed on the carcasses of large animals and search out their food by flying in circles at a height. Hovering at a height gives them the advantage of surveying a large area. This is because the effective area which they can survey is the base of a cone at the tip of which the birds fly. Greater the height of this cone, larger is the area of the base. Thus, birds flying in small circles at great heights can keep a watch on a large tract of land below to look for a meal. That is why vultures and other birds of prey like kites, hawks and raptors circle at great heights. Of course, picking up tiny animals from such distances requires sharp eyesight, which all these predatory birds have.