Category Science

Zip fastener is a fastening device in which two rows of teeth and sockets are brought together so that they interlock. Metal zips have lines of tiny teeth, while plastic zips contain small loops on each side. When you pull the slide of the zip fastener up, it pushes the teeth or loop together. The first zip was invented by Whitcomb Judson in 1893.

Beneath each tooth in a metal zip fastener is a small socket. The slide is narrow at the bottom so that it forces the teeth together as the zip is pulled up. The teeth on one side fit between the teeth on the other side. As they come together, each tooth slips into the socket under the tooth above and the zip stays closed. As the slide moves down, a divider at the top of the slide pulls the teeth apart.

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            Electric typewriters are increasingly replacing the mechanical typewriters. The first commercial typewriter was produced in 1874 by Christopher Latham Sholes. It was produced by Remington Company of USA. The first electric typewriter was marketed in the mid 1930s.

            An electric typewriter along with its functional diagram is shown in the figures. An electric typewriter involved less manual labour as compared to the old mechanical machines. The mechanism of this typewriter is more efficient.

            When a key (1) is pressed, a cam (2) makes contact with a drive roller (3) powered by an electric motor (4) The cam is propelled upwards with an even force, causing the cam lever (5) to move back. This makes the upwards movement of the appropriate type bar. (6) The paper is wound on a cylinder which moves along one character at a time during typing. A typing ribbon is forced against the paper by the metal bar, so printing a letter on the paper. As the type bar falls back, the carriage moves one character space to the left. The force of the typing strokes does not depend on the pressure applied by the typist so the results are more even. At the end of a line the typist presses a key that shifts the carriage to the right and at the same time rotates the cylinder, carrying the paper to the beginning of the next line.

            Electronic typewriters are move sophisticated than electric typewriters. Based on microchip control they are usually very quiet to use and their action is faster since they contain less moving parts. They offer more functions especially they have memory that allows user to make corrections.

           The word processor while retaining the advantages of the electronic typewriter keyboard has replaced the movement of the carriage and cylinder by the movement of a cursor on the screen. This means that mistakes can be erased and passages added, removed or repositioned before the matter is typed on the paper. 

               Aerosols were patented in the United States of America in 1914 and have been increasingly used since the early 1950s. Aerosol cans and bottles are used to spray paints, perfumes, deodorants, furniture polish, oven cleaner, pesticides and many other liquid products.

       Initially the can is filled with the product to be sprayed and the propellant. When the push button is pressed, the product is forced up the dip tube and comes out as spray from the hole in the top. The top hole is very narrow and causes the liquid to break up into a fine, mist-like spray. Inside the can, the propellant is a gas under pressure usually a chlorofluorocarbon which forces the liquid in the tube to the top. However, concern about the damaging effects that chloro-fluro carbons have on the earth’s ozone layer has forced scientists to look for alternatives. The top of the can contains a valve with a spring that closes the value when the top is released.

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               The word ‘radar’ is an acronym for ‘radio detection and ranging’. It is, in fact, an electronic device by which one can detect and measure an invisible flying object’s distance and speed. It can work efficiently under all weather conditions such as fog, mist, smoke, snow-fall, storm, cyclone, rains etc. Due to these reasons it is used in the control-room for the guidance of aeroplanes.

              The radar works on the principle of ‘echo’. The sound waves reflected by some obstacle produce an echo. Similarly, radio waves which are electromagnetic in nature also get reflected when they encounter some obstacle in their path. This property of radio waves was discovered by scientists in 1930. Using this property, in 1935 five radar centres was established in America. Major developments in the field of radars took place during the Second World War. These rendered a great help in detecting the enemy bombers. Since then, many kinds of radar have been developed for peaceful uses also. Now, there are radars which help in controlling and guiding the path of unmanned space crafts. Radars giving information relating to weather are also available. 

              Do you know how radar works? Radars make use of radio-waves, similar to those used in radio broadcasting. However, the radio-waves used in radar have higher frequencies. They are called micro-waves. The speed of these waves is equal to that of light i.e. (186000 miles) per second. The radar centre has a transmitter which sends out radio waves with the help of an antenna towards the object. It also has a receiver which receives the radio waves reflected by the object. This receiver has a screen which shows the object’s position in the sky.

             The time taken by the radio-waves in going from the transmitter to the object and in coming back to the receiver is recorded by radar. By multiplying this time with the velocity of light we get twice the distance between the radar and the object. This is how the distance of the object is determined. The radar has automatic instruments which perform all these functions. Initially, radars used to be very big in size, but now there are ones which are even smaller than our palms. 

          Atom bomb is a nuclear weapon which makes a huge explosion powerful enough to destroy a city. It is based on uncontrolled fission chain reaction. When the nucleus of a heavy element like uranium is bombarded by a neutron, it breaks into two large fragments and either two or three fresh neutrons are produced. These neutrons further collide with other nuclei causing more fissions. In this process large amount of energy is released. If the chain reaction continues, tremendous, devastating explosion will take place. This is what we call as atomic explosion.

          To make an atom bomb critical mass of uranium – 235 or plutonium – 239 undergoes fission chain reaction by stray neutrons. In this process tremendous energy is released.

          Based on fission chain reaction, the first atomic bomb was developed during the Second World War by a team of American scientists. The first atomic bomb made of uranium – 235 was dropped on August 6, 1945 on Hiroshima and three days later the second bomb based on plutonium was dropped on Nagasaki (Japan). Those have been most tragic events in the history of mankind. Destruction caused by these bombs ended Second World War.

          After this Russia, Britain, China and France also tested their atom bombs.