My Science School

Gamma rays are streams of electromagnetic waves. They are given off from elements such as radium, when they undergo a process known as radioactive decay.

     In 1899 the British physicist Ernest Rutherford began a study of radioactivity. He found three types of radiation which he called alpha, Beta and gamma rays. Alpha rays were stopped by a thin sheet of paper, beta rays could get through several millimeters of aluminum, and gamma rays could pierce quite thick pieces of lead.

      Alpha rays travel at up to 12,000 miles a second, beta rays from 80,000 to 180,000miles a second, and gamma rays at 186,000 miles a second, the speed of light.

     Gamma rays have proved very helpful in medicine and industry. These rays are also given off by radioactive isotopes obtained as by-products in production processes. They can produce radio graphs of forgings and the seams of boilers and other pressure vessels, where freedom from flaws is vital.

Picture credit: google

Pollution is a problem because man, in an increasingly populated and industrialized world, is upsetting the environment in which he lives. Many scientists maintain that one of man’s greatest errors has been to equate growth with advancement. Now “growth” industries are being looked on with suspicion in case their side effects damage the environment and disrupt the relationship of different forms of life.

       The growing population makes increasing demands on the world’s fixed supply of air, water and land. This rise in population is accompanied by the desire of more and more people for a better standard of living. Thus still greater demands for electricity, water and good result in an ever increasing amount of waste material to be disposed of.

    The problem has been causing increasing concern to living things and their environment. Many believe that man is not solving these problems quickly enough and that his selfish pursuit of possessions takes him past the point of no return before he fully appreciates the damage. It would then be too late to reverse the process.

    Ecologists say we are so determined to possess a new car or washing machine, or to obtain a greater yield from our crops by the use of fertilizers, that we ignore the fact that life depends on a lot of micro-organisms working efficiently.

     For example, if new chemicals were released into the environment, a combination of them might well poison one or more of the different type of bacteria in soil and water, which are essential to keep nitrogen being circulated from the air into organic material, and being cycled back into the air again. If this should happen on a world-wide scale, the air would become unbreathable.

Picture credit: google

An atom splits when it is struck by a neutron. The nucleus of the atom then breaks into two roughly equal parts and, at the same time, shoots out several high-speed neutrons.

      Atoms are so small that they cannot be seen under the most powerful microscope. They are the building bricks of which each element is composed. The Greek word “atom” means “cannot be cut”. But we know how that atoms can be cut, or split. Each one contains minute particle carrying two sorts of electricity: first the electrons which are negatively charged; and secondly, the central core or nucleus which is made up of protons (positively charged) and neutrons (no charge).

    In the 19th century it was discovered that all elements with atomic weights greater than 83 are radioactive and that the nucleus could be divided into several parts. Albert Einstein (1879-1955) calculated in 1905 that splitting an atom would destroy mass and release heat. By thus converting matter into heat energy, vast amounts of heat would be obtained by destroying only a very small amount of matter.

     Between 1934 and 1938 the Italian Enrico Fermi and the German Otto Hahn discovered that atoms of uranium (atomic weight 92) split when struck by a neutron. In 1939 Fredric Joliot-curie found that this splitting, or fission, released two or three more neutrons which in turn produced fission in more uranium nuclei, and so on. It is this chain reaction that makes possible not only the benefits of nuclear power but also the horrors of nuclear warfare.

Picture credit: google

If you stood on the shore looking across the sea to the horizon (the line appearing to separate earth from sky), you might be able to see about two and a half miles. But he higher you stood the farther you would be able to see. As the earth is curved, the horizon would appear farther away with every increase in the height above sea level.

       At a height of 20 feet you might see for six miles. From the top of a 300-foot cliff your view could extend for 23 miles, while on the summit of a 3,500-foot mountain, it could lengthen to 80 miles. From an aircraft flying at 16,000 feet you might have an uninterrupted panorama for 165 miles.

If you look straight up into the sky, the distance you can see is immense. The moon is about 239,000 miles away and the stars are millions of miles distant.

Picture credit: google

Radar, or radiolocation, as it was called in the early days, is the use of radio waves to find the where-about of aircraft or ships.

    Electromagnetic waves, which include radio and light waves, all travel at the same speed. When small bursts of radio waves, fired into space from a transmitter, strike an object such as an aircraft some of them bounce back and are collected by an aerial. Special equipment calculates the distance of the object from the time taken for the waves to go there and back.

    Direction is obtained by rotating the aerial, and the course being taken by the object is shown as spots of light on the face of a cathode ray tube. So direction, position and movement can be judged accurately.

    Radar was first used to detect enemy aircraft in wartime, and to guide fighter aircraft and bomber pilots. Since then it has proved invaluable in civil aviation by helping the pilot to guide his aircraft in the air and to land it safely in fog or at night.

   At sea it can give the position of land and other ships. Some buoys are fitted with radar, so that they can be located in the dark or in fog. Radar is used also to give warning of turbulent weather.

Picture credit: google

 

 

 

Ursa Minor is the name of a group of stars in the Northern Hemisphere. The word used in astronomy for a group of stars is “constellation”.

      The stars and constellations have Latin names. Ursa Minor means The Little Bear. Its brightest star is called Polaris, and is centered over the North Pole. It is of great importance in helping sailors to find their bearing when navigating at night.

    Star maps of the sky will help you locate the constellations.

Picture credit: google

A star is a body of luminous gas, like the sun. But as stars are much farther away from the earth than the sun, they appear to be only small points of twinkling light. With the naked eye it is possible to see about 2,000 stars at any one time or place but with the most powerful telescope over 1,000 million stars are visible. Although light travels at 186,000 miles a second, the light from the stars takes many years to reach the earth.

     Stars are not fixed in space, but are travelling in different directions at different speeds.  Seen from the earth, these movements appear to be so small that groups of stars, or constellations, seem to have a permanent relationship. The star patterns we see in the sky are almost the same as those seen by our ancestors hundreds, or even thousands of years ago.

    The sizes of stars vary tremendously, from less than the diameter of the sun to thousands of times its size. Most stars appear white when looked at with the naked eye, but some are bluish-white, yellow, orange and red. The varied colours are due to differences in surface temperature. The brilliant, white stars are the hottest with surface temperatures of several hundred thousand degrees. The less brilliant, orange and res stars have surface temperatures of about 2,000 degrees.

      There are exceptions, however. Te red giant, betelgeux, in the constellation (or group) of Orion, appears to be brilliant because of its size. Its diameter is 250 million miles, which is greater than the diameter of the earth’s orbit round the sun.

     Shooting stars which are sometimes seen moving across the night sky for a few seconds are really meteors. These small particles flare up as they strike the earth’s atmosphere and usually burn out.

Picture credit: google

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.

Picture credit: google

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.

Picture credit: google

The Milky Way, or Galaxy, is the whole concourse of stars and other bodies which can be seen stretched across the heavens. It includes our own sun and its planets, as well as all stars visible to the naked eye. But the name is commonly restricted to the luminous band or belt where most classes of stars are concentrated.

       The spiral arms of the Milky Way are rich in hot, bright stars, interstellar clouds of gas (mainly hydrogen) and dust. The first evidence of spiral arms was obtained in 1951 by the American astronomer W.W. Morgan, who identified three.

     Our own system of sun and planets appears to be situated towards the inner edge of one of the arms, which is about 1,300 light-years away. The Andromeda nebula, a vast mixture of gaseous and solid matter, is visible as a small luminous patch in our sky. But it is comparable in size to the Milky Way and seems remarkably similar to our own galaxy.

    The Palomar telescope, 200 inches in diameter, situated on Mount Palomar in California, has perhaps 1,000 million galaxies within the scope of its vision.

Picture credit: google

In the beginning our universe was a mass of white-hot vapours and molten materials whirling about in space. Our world was formed from this. Astronomers believe it took millions of years for the cloud to cool, contract and begin to turn into molten rock.

      Modern astronomers think that many millions of years ago there was a huge explosion in space. They do not know exactly what happened. But it is possible that our sun exploded or that a much bigger companion star of the sun became a supernova-that is, it broke up violently. The debris and blazing gases from this explosion were, it is thought, flung far into space.

      For more millions of years our solar system boiled and bubbled. But very slowly, the fiery redness began to cool and condense into the nine planets and many smaller bodies. All these planets now revolve around the sun.

     After further vast periods of time the lava of the earth began to solidify, developing over many millions of years, into the world as we know it today.

Picture credit: google

            Frost comes from the atmosphere when the temperature falls below freezing, and invisible water vapour in the air turns into white ice crystals, without first becoming a liquid. It usually occurs when the skies are clear, when there is no wind and when a mass of cold air descends on  the  land.

            This often happens during the night in the spring and autumn of areas with temperate climates. In the morning the fields and roofs are white with what would be dew if the temperature had been above freezing point. It is the most common type of frost and is often called hoar frost.

            Sometimes only the leaves of plants are fringed with white rime. This is formed when very small droplets of the moisture from fog have frozen on coming into contact with a cold object.

            There is also black frost. This occurs when water vapour turns first into liquid and then freezes into a thin layer of ice instead of white crystals. As it is invisible, it is particularly dangerous when it forms on roads.

            The beautiful patterns, looking like trees, ferns or feathers, which are sometimes seen on windows, are made when the water vapour in a cold room condenses.

Picture credit: google

       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.

Picture credit: google

      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.

Picture credit: google

            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”.

Picture credit: google