My Science School

    Natural rubber is made up of long chains of the molecule isoprene with a few cross links between the chains. These kinked, looping polymers are intertwined in un-stretched rubber. When these polymers are subjected to a stretching force, the tangled polymer opens up because of the flexible bonds between the molecules and becomes elongated. When the applied force is released, the chemical bonds in the chains try to come back to their original state. This accounts for rubber’s elasticity.

When an electrical switch is operated it produces a spark at the contact point. This spark emits electromagnetic radiation. Since radio and TV signals are also electromagnetic in nature, the bursts of electromagnetic radiation produced by a spark is also received by the radio or TV set. This produces the disturbance which is heard as crackling sounds on the radio and snowy lines on the TV picture.

  One of the laws of fusion is that the melting point of substances which expand on freezing is lowered by the increase of pressure, while it is raised in the case of those which contract on solidification. Ice belongs to the first category of substances, that is, it expands on freezing. Ice has an open structure which collapses when subjected to pressure, producing water which occupies lesser volume. That is why ice melts when subjected to pressure.

 In filament lamps a good part of the electrical energy is used up in heating the filament which in turn glows throwing light around. While in fluorescent tubes light is produced by electrical discharge in a glass tube, the inside of which is coated with a fluorescent material. The filaments at the two ends are used only to start the discharge. The discharge passing through vapours of mercury produce UV radiations which excites the fluorescent coating producing visible light. Since very little heating is involved in the process and most of the electrical energy is used in producing light, fluorescent tubes consume less power than filament lamps.

A special kind of postal system, which existed in the princely states of Travancore and Cochin, in Kerala, was known as the ‘Anchel’. It was introduced by a British officer Colonel John Monroe in 1811. He was the Resident of the English East India Company in Travancore and their political agent in Cochin. He was also the Dewan of Travancore State. In the beginning, the Anchel service was used to carry only royal implements, government letters, and flowers as offering to the Sree Padmanbhas swamy Temple at Thiruvananthapuram, owned by royal family of Travancore. Later, the system was opened to the public for a fee of one chakram (copper coin used in Travancore. One rupee was equal to 28 chakrams).

            The Anchel office was headed by an ‘Anchel Pillai’ (the post master). Each Anchel sepoy had to carry the postal articles for a fixed distance, and then hand it over to another person. It was like a relay race.

            The Anchel sepoy used to run with a metal rod fixed with bells, in his hand. The rule was that when people heard the sound of these bells they had to make way for him. Postal runners were allowed to occupy the centre of the road, and any obstruction made to the postal runners was considered a serious offence.

            The Anchel system continued even after the Travancore and Cochin states were brought together to form the Travancore Cochin States in 1949. In 1951, the department of Anchel was merged with the Central Government’s Postal Department

How does the letter that you send reach its destination? In early days, mail was carried by riders on horseback. Sometimes, boats and carriages would also carry parcels and letters. Fees had to be paid in person to the carrier, both by the person sending the mail, and the person receiving it.

        In 1858, letter boxes were introduced ob streets. People did not have to go to the post office to mail their letters or pay fees. Free delivery of service was also started by 1863. Letters and parcels were carried by train to different cities and later on, to villages in rural areas as well. The coming of railways really increased the efficiency of the postal systems, and made delivery much faster. Today, railroads, automobiles, and airplanes are all used by the Post Office to bring your mail to you as fast as possible.

The Pony Express was a fast mail service crossing the North American continent from the Missouri River to the Pacific coast. Messages were carried on horse-back relay across the plains, deserts, and mountains of the Western United States. Compared to earlier delivery services, the Pony Express was very fast.

            In 1861, telegraph wires connected New York and San Francisco, and the Pony express riders went out of business. But their courage and determination to deliver messages through rain and snow, sleet and ice, over the toughest mountain trials and harshest desert have become legendary.

Today, when you want to send your friend a message, you just send a letter. But 3000 years ago, King Solomon and the Queen of Sheba exchanged messages by carrier pigeons. These are specially trained pigeons which will find their way back home when they are released. The Egyptians and the Persians first used carrier pigeons 3,000 years ago. They also were used to proclaim the winner of the Olympics.

Carrier pigeons served many purposes during the war, racing through the skies with airplanes, or even being fitted with cameras to take pictures of enemy positions. But one of the most important roles they served was as messengers. First an important message could be written on a piece of paper. Then, that paper neatly folded and secured in a small canister attached to a pigeon’s leg. Once the pigeon was released, it would try to fly to its home back behind the lines, where the message would be read and transmitted to the proper

Probably the most famous of all the carrier pigeons was one named Cher Ami, two French words meaning ‘Dear Friend’. Cher Ami flew 12 important missions to deliver messages. Perhaps the most important message he carried was the one that saved the lives of over 200 American soldiers, though he was badly wounded by enemy fire.

            Milk is a fine suspension of fat and protein globules in a watery liquid containing milk sugar (lactose) and other dissolved substances. Normally the fat is dispersed uniformly in the form of fine droplets and hence remains as an emulsion. But when milk is heated these fine droplets tend to raise up and at temperature of about  form a thick layer of cream on the surface. When milk comes to boiling, bubbles of steam formed at the bottom of the vessel rise up and force the thick creamy layer upwards causing the milk to spill.

                                    

  Ballpoint pens have a tiny ball made of brass, steel or tungsten carbide as their writing tip. The ball is fitted into a socket and is connected to the ink reservoir by a thin tube. When we write on paper, the ball rolls due to friction between the ball and the paper. This rotating movement allows the thick ink to flow out slowly leaving a mark on the paper.

  When drawn over a smooth surface such as glass or plastic there is little friction between the ball and the surface. The ball is unable to rotate and, as a result, the ink cannot flow out. Hence we cannot write on smooth surfaces with a ballpoint pen.

     A petrol engine can’t be run with diesel or a diesel engine run with petrol because the engines and their fuels are made for each other. In a petrol engine, for instance, a spark ignites a mixture of petrol vapours and air. This is possible because petrol is highly volatile and easily vaporuizes. Diesel cannot take the place of petrol here because it is less volatile. A different strategy is used in diesel engines. Here, the air is made hot by first compressing it. Diesel is then squirted into the hot air and it burns. Besides, the compression ratio, the difference between the pressure of the fully compressed fuel mixture and atmospheric pressure is much higher in a diesel engine. That is why; diesel cannot be used in place f petrol or vice versa.

When an empty metal vessel is struck, the entire surface of the vessel is set into vibration. The air in contact with the vessel is also set into vibration producing sound of high intensity. If the vessel is partly filled, the surface area of the vessel remaining free to vibrate becomes greatly reduced. Since the total area of air that is set into vibration by the vibrating surface of the vessel also becomes much smaller than in an empty vessel, the intensity of sound also gets reduced.

   The earthing of electrical appliances is done as a safety measure. Most of the non-current-carrying metallic parts of an electrical appliance are well insulated and safe to use, but in a faulty appliance current can pass through even these insulated parts and pose a risk to the life of the user. This is because the human body allows an easy flow of electricity through itself to ground. The earthing of the appliances prevents this risk as the earth wire offers a still easier path compared to the human body to the flow of leaking current to ground, thus making the appliance safe to use.

     It is easier to balance a long pole on the palm than a short stick because of the higher position of the centre of gravity in the former which normally lies near the middle. For balancing a long pole by holding it upright on its end on our palm what we try to do is to keep its centre of gravity right above the base. As long as the centre of gravity remains straight above the base, the stick remains balanced. But being unstable, it tends to fall and the centre of gravity moves away from the vertical. With a long pole we get sufficient time to move our hand to bring its base directly below its centre of gravity thus restoring balance. But with a short stick we hardly get any time to move our palm to restore the balance and the stick falls down.

            We need to wear dark sunglasses in snow-covered areas to prevent damage to our eyes from bright light. Normally our eyebrows cut off the glare from the sky on a bright sunny day. In snow-covered areas, however, the white snow on the ground reflects back most of the sunlight producing a glare of very high intensity. Exposure to such bright light is capable of causing snow-blindness or temporary loss of sight. The use of sunglasses cuts down the glare and helps to prevent damage to our eyes.