Category Science

Why are fertilizers used on farms?

Fertilizers are used on farms to increase crop yields by ensuring that soils contain the chemical elements required by growing plants. These chemical elements include oxygen, carbon, hydrogen, nitrogen, phosphorus, potassium, sulphur, calcium, magnesium, and iron. If soils are lacking in any of these, the deficiency can be made good by the right fertilizer.

     Until the 119th century, farmers relied mainly on the application of natural fertilizers put “goodness” back into the land. They used manure from the stock-yards and, in the case of coastal areas, seaweed from the shore. Lime was also applied to prevent acidity. This method of soil rejuvenation went a long way to maintain the presence of chemical elements. But it often did little to improve soils already lacking in certain chemicals.

      Nowadays soils are analyzed to find out deficiencies which can be made up by the application of the appropriate chemical fertilizers. Of course, the chemicals alone do not guarantee a successful crop. The continued application of the natural fertilizers, such as manure and humans (decayed vegetables matter) is also essential.

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When was the telephone invented?

Alexander Graham Bell (1847-1922) invented and patented in 1876 the first telephone that was of any real practical use. In 1874 he said: “if I could make a current of electricity vary in intensity precisely as the air varies in density during the production of sound, I should be able to transmit speech telegraphically.” This is the principle of the telephone.

      On March 10, 1872, the first historic message was telephoned to Thomas A Watson, Bell’s assistant, who was in another room: “Mr. Watson, come here; I want you.”

     Bell’s first machine gave electrical currents too feeble to be of much use for the general public. In 1877 the American scientist Thomas A. Edison (1847-931) invented the variable-contact carbon transmitter, which greatly increased the power of the signals.

    The telephone was immediately popular in the United States, but Bell found little interest in Britain when he visited the country in 1878. Then Queen Victoria asked for a pair of telephone and the royal interest resulted in a London telephone exchange being formed in 1879 with eight subscribers.

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Why don’t Cranes topple over?

Cranes do not topple over because their jib or booms are counter-balanced at the opposite end from the lift load, thus keeping the centre of gravity over the base.

     The first cranes were simply long poles fixed in the ground at an angle, with a pulley at the top through which passed a rope. They were called “cranes” because they looked rather like the neck of the bird with the same name.

     The derrick crane, which looks like a gallows, is named after Dick Derrick, a 17th century hangman. In the middle of the 18th century, steam engines began to be used on cranes, while today the lifting may be done by varieties of power.

    Jib cranes may be portable being mounted on a portable being mounted on a wheeled carriage, or they may be self-propelled. Gantry cranes with long booms are used for unloading ships while overhead cranes are used in factories. Goliath cranes, with steel towers at either side, capable of lifting 200 tons are used at some atomic power stations.

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Why did the continents drift apart?

       One of the most convincing explanations of why the continents drifted apart is that the earth expanded considerably after its creation. This theory can illustrate by imagining the earth as a balloon and the continents as pieces of paper stuck on the outside. As the balloon is blown up the pieces of paper will grow farther apart.

      Other theories suggest that the continents only appeared to drift apart because masses of land were drowned under volcanic waters. But it has been demonstrated that land masses are, in fact, made to drift, by the heat generated from the earth’s interior and from earthquakes.

       Probably a combination of various theories may be necessary to provide a complete explanation.

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Where do earthquakes occur?

      Earthquakes occur mainly in the regions of the earth where mountains are being formed, and where the earth’s crust is under strain.

      Some mountains are formed of great thickness of folded sedimentary rock laid down beneath the sea. Heat currents deep within the earth are thought to suck down sections of the undersea crust and so produce great trenches thousands of feet deep. When the heat currents die away the material forming the bottom of the trench begins to rise because it is lighter in weight. Eventually it is thrust up as a mountain range.

    This is never a smooth process but is accompanied by great friction and heat, as well as by rending and shearing and tearing of deep underground rocks connected with mountain formation cause earthquakes. Even small underground movements may produce violent surface shocks. The great Tokyo earthquake of 1923 which is believed to have killed 25 million people was caused by the twisting of a section of the earth’s crust in Sagami Bay.

     As might be expected, ocean trenches are the seat of a great many earthquakes, for there the earth’s crust is in an unstable sate. Indeed all the deep earthquakes those taking place more than 160 miles below the surface-originate around the Pacific trenches. About 90% of the intermediate earthquake (30 to 160 miles deep) also originates there, as do 40% of the shallow earthquakes (less than 30 miles deep).

      Some shallow and intermediate earthquakes are caused by volcanoes or by a slight shifting of layers of rock at a weak place or “fault” on the earth’s surface. One of the most famous and widely publicized of these is the San Andreas Fault on which San Francisco is built.

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When was the sextant invented?

            The sextant was invented in England in 1732 by John Hadley. Hadley’s instrument is used mainly at sea to determine a ship’s latitude, or distance from the equator. Its invention laid the foundation of modern navigation with the aid of the sun and stars.

              The instrument is so called because it is equipped with an arc which is usually one-sixth of a circle, or 600. It measures the angle of the sun’s or a star’s altitude above the horizon. As this angle varies with the distance from the equator, the information obtained helps the navigator to calculate his position. All he needs in addition is the time, the date and the longitude which can be found by comparing local time with the time at Greenwich.

         To operate the sextant, the navigator looks through its small telescope straight at the horizon. At the same time, an image of the sun is reflected by mirrors into the user’s field of vision. When the sun is made to appear exactly on the horizon, the arm which moves the mirrors gives the required measurements to calculate the ship’s position.

       The handling of a sextant is generally to as “shooting the sun”.

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