Category Science

How does a battery torch work?

            A battery torch is a portable electrical appliance used for lighting. It has a variety of uses. Doctors use it to examine closely the ears, eyes, noses and mouths of the patients. Do you know how a torch produces light?

            A battery torch can be divided into four main parts: the battery, bulb, case and the switch. The battery is in the form of dry cells. Dry battery cells such as those in torches, transistors or calculators produce electricity only for a limited time. Most of the torches make use of two or three dry cells. The body of the torch is fitted with a bulb and dry cells. When the switch of the torch is pressed, the cells get connected to the bulb, and as a result of this the bulb emits light.

            The torch produces light by connecting the positive and negative terminals of the dry cells to the bulb. The current passes out at the positive contact through the bulb and returns back via the negative contact, thus making a complete circuit.

            When the switch is moved to the ‘on’ position, a metal piece inside the case touches the positive terminal of the battery, letting the electricity flow out to the bulb. In some other torches, the battery is pushed up so that the positive contact touches the bulb itself. In a battery torch, there is a reflector which reflects back the light to long distances.

 

How does a screw jack work?

          Almost all drivers of heavy or light vehicles always carry a screw jack with them for the simple reason that it alone performs the role of several people in hours of emergency. A jack is essential equipment for raising heavy objects off the ground, usually used to remove or adjust wheels of automobiles. The screw jack is a simple machine like pulleys or levers and is used for raising large loads with a little human effort.

          A simple screw jack comprises a rod in which a square screw thread has been cut, a base plate in which this can rotate and a block (or nut) through which the screw threads runs. This block is shaped in such a manner that it hooks on to the underside of the car. When the screw is rotated by a thin rod or a tommy bar, which passes through a hole in the screw, the block is slowly raised or lowered.

          A screw thread is in fact a spiral cut made in the rod so that the screw may be regarded as a spiral inclined plane. For each complete turn of the screw it advances the same distance. This distance is the pitch of the screw, which can also be found by measuring along the length of the screw which is the distance between any two adjacent ridges of the thread. The screw of a screw jack whose diameter is 3/4 inch may have six threads per inch, so the pitch of the thread is 1/6 inch. Thus, for every one complete revolution of the tommy bar the lifting block moves 1/6 of an inch up or down.

          The velocity ratio of any machine is found by dividing the distance ‘e’ through which the effort moves by the distance ‘I’ through which the load is raised. If the tommy bar is a little more than 6 inches in length then it will trace out a circle of radius of 6 inches for each complete revolution. The circumference of this circle is about 37.7 inches so that the load is raised by 1/ 6 inch for every 37.7 inches that the effort moves. The velocity ratio of the screw jack can be calculated.

          Even if the thread of the screw is kept clean and well greased, there is still likely to be considerable friction between the screw and the lifting block as well as the base plate. Thus a load of 225 kg, which is the weight supported by one of the four wheels of an average family car, could be lifted by a 1.25 kg effort if there were no friction. But in practice the effort would be between 3.4 kg to 4.5 kg. in other words, an ideal machine which requires no energy to move its component parts, the velocity ration is equal to the mechanical advantage.

          On account of the large frictional forces between the screw and the block, the load cannot ‘unscrew’ itself and run back under its own weight.

 

Why are crocodiles so dangerous?

          A crocodile is a large reptile with a long cigar-shaped body, short legs and a powerful tail and jaws. They have a heavy body covered with bony scales. Its pointed snout and long partially exposed sharp teeth distinguish it from an alligator (another species of the same family). A crocodile is generally more aggressive than an alligator and may attack large animals such as deer or even human beings. Caymans and Gavials are the largest living reptiles of this family.

          All the crocodiles are carnivores and live in water. Since their eyes and nostrils are located a little higher than the rest of their head, they can hide in water staying almost completely submerged and still able to breath and watch the movement of their prey. They are particularly successful in catching smaller animals because they can float closely up to their prey without being seen. Once they catch their prey they slowly tear it apart in bits by gripping with the teeth and turning it over and over again. The crocodiles have been seen mysteriously more aggressive when protecting a nest or when the water is drying up. They usually feed on fish, birds and small mammals.

          The crocodiles live in tropical areas throughout the world, usually in swamps or marshes, or along slow-moving rivers. They have webbed feet which help them walk on wet or muddy ground. 

How is Nightingale distinct from other birds?

               In the kingdom of birds, nightingale enjoys a unique status for its ability to sing. This quality of nightingale has made it quite popular with poets and no bird has been written of so much by the poets as the nightingale. Aristophanes, the great Greek poet wrote about it in the 4th century B.C. and Keats in the 19th century.

               According to the poets, the nightingale sings only at night  and in almost any season of the year. But this goes against the facts as the bird sings both in the day as well as in the night. Poets had a wrong perception because they could hear it only in the night and not in the day. The reason for this being that the song of nightingale is not audible in the day as it is being overshadowed by the chirping of other birds but it is distinctly heard in the silence of the night. Again, since nightingale is a migratory bird hence its voice is generally not heard throughout the year at a particular place. From season to season, it migrates to different places. 

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How do plants and animals defend themselves?

                    Almost every plant and animal in the world has enemies that threaten its existence. So to protect itself every living being has developed some defence mechanism. Sensing the danger some organisms hide, others run, while others just fly away. 

                 Some organisms can even hide without moving. They use ‘camouflage colouring’. That means that their skin colour blends in with the matching colour of the surrounding area so well that the enemies cannot see them. Chameleon has the capacity of changing its body colours. If it is on a green leaf, it turns green; if on a brown twig, it turns brown. Some rabbits change colour with the season. The snowshoe hare is brown in summer and white in winter. The white fur camouflages the rabbit in the snow. Another phenomenon called counter-shading is a common type of camouflage among the fishes. The underside of their body is of lighter shade than the top. This helps the fish to blend in with many shadows it might make. Some other animals have a remarkable ability to take the form and colour of some other object around them. Camouflage also helps some animals catch their food. Since they can blend in with their surroundings, their victims can’t spot them immediately, and thus get caught.

                    Then there are other animals such as antelope who can run very fast. Others may dodge back and forth, like a rabbit. Birds can escape most predators by flying away. 

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Which animals are extinct now?

               The study of the fossils has revealed that hundreds of species of animals and plants have come and gone since the creation of earth. To begin with, these species became extinct as a result of natural causes. The animals and plants that disappeared were those that were unable to adapt fast enough to the changing conditions of the earth or were unable to compete with their rivals for the available food supplies. However, there are other instances, such as the case of dinosaurs, in which the reason of their extinction is still not very clear. The animals which became extinct millions of years ago were never seen by man. Also there are some others that were alive only a few hundred years ago and man himself has been responsible for killing them and causing their extinction. Do you know which animals became extinct during the last few hundred years? 

             

 

                   There was a bird called dodo which became extinct by the end of 17th century. This bird lived on the small island of Mauritius in the Indian Ocean and had no proper wings to fly. For this reason people called them dodos which means ‘simpleton’ or ‘stupid’. It was hunted down by the Dutch sailors who landed in the island in 17th century. Dodo meat was good to eat and hence carried away in ships by the Dutch. Dogs and rats started eating dodo eggs and chicks. As a result all dodos vanished by the middle of 17th century. The same story marked the extinction of another bird called the Great Auk. This penguin-like bird lived on the islands north of Scotland as recently as the mid-19th century. Egg collectors and hunters drove it to extinction by 1844. 

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