Category Science

What is the International Date Line?

            The International Date Line is an imaginary line extending from the North Pole to the South Pole. It passes through the Pacific Ocean where, according to an international agreement, the date changes. As the Earth rotates, each day begins and ends on this line. 

            The date line is a consequence of the worldwide use of time-keeping systems arranged in such a manner that the local noon corresponds approximately to the time at which the Sun crosses the local meridian of longitude. The line is necessary because the Earth is divided longitudinally into 24 one-hour tie zones (15 degrees longitude each) which make one full day on Earth. Since Earth rotates eastward, the time on the clock progresses westward round the world. Thus 12 O’clock noon occurs in London (0 degree longitude) five hours before it does in Washington D.C. (75 degrees west of London), and eight hours before at San Francisco (120 degrees west of London). So, when it is noon in London, it is midnight at the place 180 degrees to the west.

            On either side of the 180th meridian, the time is the same. Let us take the example of a traveller going completely around the Earth, carrying a clock that he advanced or retarded by one hour whenever he entered a new time zone, and a calendar that he advanced by one day whenever his clock indicated midnight. When he returns to his starting point he would find that the date according to his calculations was different by one day from the date kept by persons who had remained at the starting point. That’s why a traveller moving eastward across the line sets his calendar back by one day than the one travelling westward. It has a strange effect. That means if you cross the date line going eastward, you gain a day while those travelling westward lose a day.

            The date line, however, has some variations from the 180th meridian to allow for land areas or islands. The line bulges eastward through the Bering Strait to take in eastern Siberia and then westward to include the Aleutian Islands with Alaska. South of the equator, it bulges eastwards again to allow various island groups to have the same day as that of New Zealand.

 

How does a parachute work?

               A parachute is an umbrella like device used for slowing down the descent of a body falling through the atmosphere. Originally it was conceived as a safety measure against a probable plane crash or some malfunctioning in a flying aircraft. The parachutes have now found wide applications in times of war and peace; for safe dropping of supplies of essential items in times of emergency as well as for landing of personnel. The first man to demonstrate it was Louis-Sebastian Lenormand of France in 1783. Andre-Jacques Garnaria was first to use a parachute on regular basis demonstrating a number of exhibition jumps including one from a height of about 2400 m in England in 1801.

               Early parachutes were made of canvas and later silk also came to be used. Captain Albert Berry of the U.S. Army made the first successful descent from an aeroplane in 1912. In World War II, parachutes were used for a variety of purposes; landing of special troops for combat, infiltrating agents into every territories and dropping of weapons etc. The modern man-carrying parachutes are made of nylon and are about 7 to 9 m wide when open. The cargo parachutes may be as wide as 30m when open.

               Now the question arises how does a parachute work?

               A parachute operates on a simple principle involving the force of gravity and air resistance — the two forces that act upon any falling object. The parachutes start falling towards the ground due to the pull of the force of gravity but the speed of the fall is checked substantially due to the resistance of air. At low speeds the pull of gravity is stronger than the resistance of air and at higher speed, the air resistance becomes more. Also, large flat surfaces offer more resistance than sharp surfaces. At a certain point the object reaches a speed called terminal velocity when air resistance and the pull of gravity are evenly balanced and, thereafter, the object starts falling at a constant speed. Therefore, an object shaped like a saucer reaches its constant velocity sooner. So it falls more slowly than one shaped like a needle.

               As soon as the parachute canopy opens fully, the resistance of air slows down the descent of the parachutist so suddenly that he is jerked sharply. Now even parachutes with holes or slots in their canopies have been developed to reduce the force of these opening shocks.

                The parachutes descend at a rate of about 5 m (15 ft) per second or slightly faster. But if dropped from less than 150 m above the ground, it can prove dangerous because this height does not allow the parachutes to open. The parachutists can control the direction of their descent by pulling on the shrouds and other operational devices.

               Nowadays new parachutes have been developed which enable one to escape from supersonic planes. Parachute-jumping has become a popular sport in the United States and Europe. Today there are many clubs who organize national and international jumping events in which parachutists try to land on small targets on the ground.  

 

What is a prime number?

          Any positive integer which is greater  than one and divisible by only itself is called a prime number. For example 2,3,5,7,11,13,17,19,23,29, etc. are all prime number – numbers that cannot be split by division by any other number except 1 and the particular number itself.

          The prime numbers lie at the very roots of arithmetic and have always fascinated those dealing with figures. We can take the sequence of the above given series of prime numbers as far as we like, but we will never find a prime number divisible by another. Over the centuries, the world’s greatest mathematicians have tried to do so and always fail, although they have also been unable to prove that no such number exists.

          Every positive integer greater than one can be expressed as the product of only a single set of prime numbers. Despite the fact that prime numbers have been recognized since at least 300 B.C. when they were first studied by the Greek mathematician Euclid and Eratosthenes. Still these numbers have not yet unfolded certain mysteries relating to them.

          There is infinity of prime numbers and in theory anything may happen in infinity. But so far theorists have not been able to even find any particular rule or theory governing the gaps between prime numbers, which still remains a great mathematical mystery.

          However, the highest known prime number was discovered in 1992 by analysts at AEA Technology’s Harwell Laboratory, Oxon. The number contains 227832 digits, enough to fill over 10 fullscap pages. 

What is Electricity?

               In ancient times, man had no idea of electrical energy. They took the flash of lightning during a thunder storm to be a signal for an impending destruction from the heavenly Gods. With the passage of time, science in its own way explained the mystery of this great energy called electricity.

               Today, we cannot imagine the normal life without electricity. Commonly we know it as a form of energy, that powers almost all machines or mechanical devices — trains, radios, television sets, freezers and so on. Electricity is a phenomenon involving electrical charges and their effects, when at rest as well as when in motion.

               Electricity that we use flows through wires as electric current. In a nutshell, when an electric current flows through a conductor of finite resistance, the heat energy is continuously generated at the expense of electrical energy. The particles of a matter may be positive, negative or neutral. We know that electricity has its two important particles — protons and electrons. Electron is negatively charged while proton is charged positively to an equal extent. The object containing an equal number of protons and electrons is electrically neutral. For example, anode is a positive electrode while cathode is a negative one. Bulk of the electricity we use is produced in power stations. In the generator of a power station, coils of wire are made to rotate between powerful magnets in order to rotate electric current through the coils. Electricity travels through substances like copper, aluminium and iron. These are called conductors. However, electricity cannot pass through some materials like rubber and glass and these are called insulators. 

               Electricity which flows in one direction and then in the opposite is called Alternate Current (A.C.). Each movement of A.C., back and forth, happens very quickly – about 50 times a second. The electricity that flows in our houses is mostly A.C. Steady flowing current in one direction only is known as Direct Current (D.C.). For instance, battery current is D.C.

               Soon after the invention of electric cell by Alessandro Volta, people came to know that heat, light, chemical reactions and magnetic effects could be produced from electricity.

               As early as 600 B.C. Greeks discovered electricity by rubbing Amber with cloth which enabled it to attract small pieces of papers. In fact, the word electric originated from the Greek word Electron. Based on the theory of “Electro-Magnetic Induction” of Michael Faraday in 1831, first successful generator or Dynamo was made in Germany in 1867. USA produced; electricity by running turbines with the help of falling water in 1858.

               Subsequently hydel and thermal power stations came into existence all over the world. During the 20th century many nuclear power stations were established to meet the growing demand of electricity. 

What is a pyrometer?

          A pyrometer is an instrument used for measuring high temperature – especially those which can’t be measured through ordinary thermometers. For example, pyrometers are used to measure temperature in a furnace. 

          There are two main kinds of pyrometers: the radiation pyrometer and the optical pyrometer. In a radiation pyrometer, the radiation from the hot object is focussed onto a thermopile which is a collection of thermocouples. When the thermopile gets heated due to the intercepted radiation, it produces a voltage. The amount of voltage developed depends upon the temperature. Proper calibration permits this electrical voltage to be converted into the temperature of the hot object.

          Sometimes a bolometer is used instead of a thermopile. A bolometer has two strips of the platinum metal. When the platinum strips heat up, the electrical resistance of the strips changes. The change of resistance can be used to measure the temperature. 

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What is solar wind?

            The solar wind is the constant flow of charged particles from the sun. These particles include protons, electrons and some nuclei of heavy elements. They are accelerated by high temperatures of the solar corona or outer region of the sun, to velocities high enough to allow them to escape from the sun’s gravitational field. Recent researches using satellites have shown that the solar winis made up of plasma, i.e. ionized gas, mostly hydrogen and helium, containing nearly an equal number of protons and electrons.

            The solar wind streams from the sun though outer space at a speed of about 480 km (300 miles) per second. It takes the particles about 3 days to reach Earth.

            In 1958, the American physicist, Egune Norman Parker, called this outward system of protons — the solar wind.

            The solar wind causes the tails of comets to change direction and point away from the sun. It also causes magnetic storms which may disrupt radio communications on Earth. The solar wind causes ionization of the gases in an upper atmosphere, resulting in the coloured light phenomena known as auroras.

            When the solar wind encounters Earth’s magnetic field a shock wave results, the nature of which is not fully understood. That part of the solar wind which does not interact with Earth or the other planets continues to travel at supersonic speeds upto a distance of approximately 20 astronomical units (one astronomical unit is about 1.5 x  kms). As it passes through a similar shock phenomenon it loses this supersonic characteristic. Here the gas cools off and eventually diffuses into the galactic space.