Category Science

Why do rivers meander?

            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.

Why do clouds float?

            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.

Why is skating possible on ice?

            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.

Why is there a scent after it rains on parched soil?

            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.

Why do the dry beds of ponds and lakes crack?

            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.

Why are birds perching on electric lines not killed?

For any living being to get electrocuted, a current of sufficient voltage has to pass through its body, i.e. there should be completion of the electric circuit. Birds perching on live electric transmission lines are not killed because they are in contact with only on wire and no current passes through them. But if the bird sitting on a live-wire simultaneously comes in contact with the ground or touches another live-wire, the electric circuit would be complete and the bird will be killed by the current flowing through it. Similarly a person hanging on to a single live-wire will not be electrocuted unless he touches the ground or the earth wire.