Category Science

What is weightlessness?

          Man experiences weightlessness in a spacecraft. Anything that is not fixed or tied down just floats. Astronauts have to use special devices to eat and drink. The crew members have to learn to adjust the vigour of their actions to keep from crashing into the walls and equipments. During sleep also astronauts feel unstable and that is why they use belts during sleep. Let us understand more about this phenomenon. 

          The mass of a body is the amount of matter contained in it. In fact, it is the measure of inertia of the body. The weight of a body is the force with which the body is attracted towards the centre of the earth. Weightlessness occurs when there is no gravitational pull on the body such as in a spacecraft or when a satellite orbits the earth. If the force of gravity is balanced by the centrifugal force, the man in the spacecraft experiences a state of weightlessness. A body falling freely under gravity also experiences weightlessness.

          Sometimes, weightlessness causes nausea and giddiness because the working of the balancing organs in the inner ear gets upset. Particles floating in the spacecraft do not settle down easily and may be harmful for health. Astronauts are able to adapt to weightlessness through training.

         To make up for lack of gravity, regular exercise is essential in a spacecraft to keep the muscles in a good condition. It has been observed that in space, astronauts tend to ‘grow’ taller. This is because the pads of cartilage between the bones of the spine are no longer under pressure from gravity, and they expand. This increase in height can be as much as 5 cm. However, the astronaut returns to his original height when he returns to earth.

          Under the conditions of weightlessness it is possible to conduct certain scientific experiments that are impossible on earth. Absolutely perfect crystals can be grown and alloys of very high homogeneity can be made under the conditions of weightlessness which are very difficult to make under the pull of gravity.

          Scientists have been conducting experiments to find out whether a woman may become pregnant in weightlessness condition — and if so, what could be the effect of zero gravity on such children. In recent years, it has been discovered that prolonged periods of weightlessness can cause depletion of calcium in astronauts. 

What was the Ice Age?

          Ice Age was those early periods of the earth’s history when most of the northern part of the earth was covered by a vast sheet of ice.

          During the earth’s long history, there have been several ice ages. The earliest was in, what is called the late Pre-Cambrian times, some 700 million years ago. Another ice age occurred during the late Carboniferous and early Permian periods, about 280 million years ago. Finally about 2 million years ago, an ice age began which lasted nearly until our own times. This is known as the Pleistocene Ice Age. Here we shall discuss about the Pleistocene Ice Age only because information about the first two Ice Ages is not available.

          The Pleistocene Ice Age consisted of four periods. During each period, the ice formed and advanced southward, then melted back towards the North Pole. This happened four times. The ‘cold periods’ are called ‘glacial ages’ and the warm ones (when the ice melted) are known as ‘interglacial periods’. 

          The first period of ice came about two million years ago, and is known as Nebraskan. The second period came about 12,50,000 years ago and is called the Kansan. The third one came about 500,000 years ago. It is called the Illinoisan period. The fourth period, known as Wisconsin period, came about 100,000 years ago.

          In between these glacial periods, there have been three interglacial periods. These interglacial ages are called the Aftonian, the Yarmouth and the Sangamon Ages. A typical glacial age lasts about 40,000 to 60,000 years, and interglacial age lasts about 40,000 years. Ice of Wisconsin period began to melt about 40,000 years ago and ended some 10,000 years ago. According to geologists, the earth at present may be in an interglacial age.

          Geologists have learnt a lot about ice ages by studying fossils. Whole of Canada and one-third of northern United States, as far as New York City and the Missouri River valley, were covered by ice. In places the thickness of ice was from 2400 to 3000 m (8000 to 10,000 ft). In Europe ice covered whole of northern Europe, the British Isles and much of northern Russia. During the Pleistocene epoch, more than 30% of the earth’s surface was covered with ice.

          Plants and animals, too, were much affected by the advance and retreat of ice. A number of new animals such as camels, cattle and modern horses appeared during this Ice Age. Many lakes, such as the Great Lake of North America, were also formed during this period. 

Why is it harder to walk uphill than downhill?

            Generally while climbing up the stairs of a building, a person gets more easily exhausted, than while coming down. To lift heavy articles, greater effort is required. It is harder to walk uphill than downhill. Have you ever wondered why?

            We know that our earth attracts everything towards its centre. This is known as the force of gravity of the earth. It is the force of gravity that holds us on the surface of earth. When we move away from the earth’s surface, we have to do work to overcome the force of gravity. 

 

            So while going uphill, our muscles have to do more work to lift the weight of our body against the gravity of the earth. For this the heart has to pump more blood to the cells. As a result, our lungs have to do more work to pump out the carbon dioxide from the heart, and to replace it with oxygen. Hence for a steep climb we breathe more quickly.

            If we climb a mountain by two different paths — one more steep, and the other less — we would feel greater fatigue in the case of the steeper one.

            In comparison to the energy required for walking on a horizontal plane, the total value of the extra energy needed for climbing is the weight of the body multiplied by the total height to be climbed. 

Continue reading “Why is it harder to walk uphill than downhill?”

How do deep-sea divers operate?

           Since ancient times, man’s curiosity has led him to explore the dark, mysterious world of the deep seas. Diving has therefore developed to be an important sport over the years. But how do men stay under water for long periods of time?

          The first practical diving apparatus was devised by a German scientist, named Augustus Siebe in 1819. It comprised a metal helmet with a shoulder plate attached to a waterproof leather jacket. A tube running from the helmet was attached to an air pump. This was the first of many major experiments he carried out in trying to perfect a safe method of staying and working under-water. In 1830 he designed and developed a complete suit and helmet with air valves. Although many improvements have since been made, Siebe’s principles remain in universal use. 

          Deep sea divers, such as those who search shipwrecks for treasure, are divided into groups. They are skin divers who wear rubber suits that fit tightly like the skin, and divers known as ‘hard hats’ who wear heavy diving dress.

          A deep sea diver should use seven essentials: (a) An air pump for pushing air downwards to him. (b) A helmet, usually of steel, with glass windows to see. (c) A flexible waterproof suit fitting closely at wrists and ankles. (d) A length of air tubing that must be flexible, but must not collapse under the pressure of water. (e) A pair of heavy boots to keep the feet on the bottom. (f) Lead weights, hooked to chest and back, to prevent floating up to the surface. (g) A life-line to communicate with the surface by a system of jerks. One jerk may mean danger, and so on!

          Some divers also have a telephone so that they can talk to the ship. The wires for these telephones are built into the lifelines.

          Water pressure is a big problem for deep sea divers. The deeper a diver goes, more becomes the pressure of water around him. So the air pumped down must enable him to breathe properly and also balance the water pressure outside.

          In the past, deep sea divers used to breathe ordinary air, which contained nitrogen.

          This was very dangerous because when the pressure was very high, nitrogen would dissolve in the blood. When the diver surfaced, the pressure quickly returned to normal, which caused the nitrogen to bubble out of the blood. This led to a very painful illness which could even kill the diver, called as ‘Bends’ or ‘Caisson disease’. To avoid this, divers now breathe a mixture of oxygen and helium. Helium does not dissolve in the blood, so it is safer to use. But breathing helium makes divers speak with a high, squeaky voice because sound travels three times as fast as it does in air!

          In recent years, diving has not only become a popular sport, but is also useful in performing important jobs. Divers are needed for the construction and repair of bridges. They study plant and animal life beneath the surface of water. They aid in finding drowned people, and they also help in the search for buried treasure! 

 

How many stars can we count at night?

            On a clear night, if we look up at the sky, we will see innumerable stars — small and big, bright and dim. Have you ever tried counting them? You’ll be surprised to find that out of these innumerable stars about 6000 can be seen without the help of a telescope!

            That does not mean that a person can just look up and count 6000 stars. From any one place on earth, only one-half are visible at one time as the rest of them are on the other side of it. Many of the stars near the horizon cannot be seen on account of haze. Hence if someone starts counting the stars, he would probably not be able to count more than 1000 of them. 

            By using a very powerful telescope we can see even very dim and distant stars. This way it would be possible to photograph more than 1,000,000,000 stars. Today astronomers have succeeded in identifying more than 4,57,000 stars.

            Now the question arises – why can’t we count more stars?

            Stars vary considerably in size, temperature, brightness and distance from the earth. We can count only those stars which are bigger in size, nearer to the earth, and bright enough to be seen by naked eyes. We can’t see the faint, smaller and distant stars without a telescope. However if we take a photograph from the same place by attaching a camera with the telescope, we can count more stars on the photograph, than we would with the naked eye. 

What are Black Holes?

          Twentieth century astronomers have predicted dark areas in space. The gravitational attraction of these areas is so high that anything which goes into it cannot come out. Even light cannot escape their gravitational pull. Hence they do not emit light. These areas are called Black Holes or collapsars.

          A German astronomer, Karl Schwarzschild predicted the existence of black holes in 1907. He theoretically proved that black holes are the end results of all stars whose mass is much greater than that of the sun. The existence of black holes was first theoretically proved in 1939 by J. Robert Oppenheimer and Hartland S. Synder as a consequence of General Theory of Relativity. 

          Let us consider a star whose mass is greater than that of the sun. Its size remains normal due to the balance between the two forces — one being the expansion force caused by the enormously high temperature which tends to expand the star’s material, and the other being the enormous gravitational pull which tends to contract the star’s substance.

          At some stage in the star’s life, after thousands of millions of years, its nuclear fuel decreases causing a fall in its core temperature. As a result, the gravitational pull becomes stronger than the expansion force. Gradually the star begins to collapse.

          In this process, the atoms present in the star break into electrons, protons and neutrons. The mutual repulsion between the electrons prevents further contraction. The star, at this stage, is known as ‘White Dwarf’. In this process, the star is reduced to one-hundredth of its original size; thereby the gravitational pull in the White Dwarf becomes about 10,000 times more than the original value.

          Under certain conditions the gravitational pull becomes strong enough to overcome the electron repulsion. The star begins to contract further and in this process of contraction, electrons and protons combine to form neutrons. The star at this stage is called “Neutron Star”. Its size is now reduced to five hundredth part of the dwarf star and the gravitational attraction becomes about 100,000,000,00 times that of the original star.

          The light emitted from the neutron star reduces its energy and as a result its size further decreases. At some stage, no radiations come out from this star. It is then called a Black Hole which is the smallest and most dense object in the universe.

          Scientists are still looking for evidence of the actual existence of black holes in the universe. They have detected Cygnus X-1 as a black hole in 1974. In 1983, US astronomers detected another X-ray source in the large Magellanic cloud.