Category Every Day Science

WHAT IS A PERISCOPE?

A periscope is a metal tube that can be extended above the submarine while it is underwater. The tube contains lenses and mirrors, which enable an image of the scene above the surface to be seen below in the submarine. The periscope can swivel, so that a 360° view is obtained. The operator turns the periscope by means of the handles on the side. These fold up when it is not in use, as space is always at a premium in a submarine.

Periscope, optical instrument used in land and sea warfare, submarine navigation, and elsewhere to enable an observer to see his surroundings while remaining under cover, behind armour, or submerged.

A periscope includes two mirrors or reflecting prisms to change the direction of the light coming from the scene observed: the first deflects it down through a vertical tube; the second diverts it horizontally so that the scene can be viewed conveniently. Frequently there is a telescopic optical system that provides magnification, gives as wide an arc of vision as possible, and includes a crossline or reticle pattern to establish the line of sight to the object under observation. There may also be devices for estimating the range and course of the target in military applications and for photographing through the periscope.

The simplest type of periscope consists of a tube at the ends of which are two mirrors, parallel to each other but at 45° to the axis of the tube. This device produces no magnification and does not give a crossline image. The arc of vision is limited by the simple geometry of the tube: the longer or narrower the tube, the smaller the field of view. Periscopes of this type were widely used in World War II in tank and other armoured vehicles as observation devices for the driver, gunner, and commander. When fitted with a small, auxiliary gunsight telescope, the tank periscope can also be used in pointing and firing the guns. By employing tubes of rectangular cross section, wide, horizontal fields of view can be obtained.

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HOW DOES A SUBMARINE SUBMERGE AND SURFACE?

Submarines, unlike most ships, are not always required to float! In order to make a submarine sink beneath the surface, its density must be increased to be greater than that of the water. This is done by taking in water, which fills ballast tanks within the outer hull of the submarine. The amount of water entering can be controlled, so that the vessel sinks slowly. To bring a submarine back to the surface, pumps force the water out of ballast tanks. The submarine’s density becomes less than that of the water it is displacing, so it rises.

To control its buoyancy, the submarine has ballast tanks and auxiliary, or trim tanks, that can be alternately filled with water or air. When the submarine is on the surface, the ballast tanks are filled with air and the submarine’s overall density is less than that of the surrounding water. As the submarine dives, the ballast tanks are flooded with water and the air in the ballast tanks is vented from the submarine until its overall density is greater than the surrounding water and the submarine begins to sink (negative buoyancy). A supply of compressed air is maintained aboard the submarine in air flasks for life support and for use with the ballast tanks. In addition, the submarine has movable sets of short “wings” called hydroplanes on the stern (back) that help to control the angle of the dive. The hydroplanes are angled so that water moves over the stern, which forces the stern upward; therefore, the submarine is angled downward.

To keep the submarine level at any set depth, the submarine maintains a balance of air and water in the trim tanks so that its overall density is equal to the surrounding water (neutral buoyancy). When the submarine reaches its cruising depth, the hydroplanes are leveled so that the submarine travels level through the water. Water is also forced between the bow and stern trim tanks to keep the sub level. The submarine can steer in the water by using the tail rudder to turn starboard (right) or port (left) and the hydroplanes to control the fore-aft angle of the submarine. In addition, some submarines are equipped with a retractable secondary propulsion motor that can swivel 360 degrees.

When the submarine surfaces, compressed air flows from the air flasks into the ballast tanks and the water is forced out of the submarine until its overall density is less than the surrounding water (positive buoyancy) and the submarine rises. The hydroplanes are angled so that water moves up over the stern, which forces the stern downward; therefore, the submarine is angled upward. In an emergency, the ballast tanks can be filled quickly with high-pressure air to take the submarine to the surface very rapidly.

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ARE SHIPS STILL IMPORTANT NOW THAT AIR, ROAD AND RAIL TRAVEL ARE SO MUCH FASTER?

Ships are of vital importance to the world’s economy. They carry over 90% of the freight that travels around the globe. Although air travel is a quicker way of crossing the oceans, it is very expensive, and weight is always a problem. Ships may be slower, but they can carry enormous loads. Nowadays many loads are carried in large steel containers, which can be stacked on the ship and then lifted by crane directly onto the back of a truck in the port, doing away with the need to pack and unpack cargo at each change of carrier. Containers protect the goods inside. They can be stored in stacks on the dockside until transferred to a ship, truck or train.

Ocean shipping is the primary conduit of world trade, a key element of international economic development, and a central reason why the world enjoys ready access to a diverse spectrum of low-cost products. Seventy-five percent of internationally traded goods are transported via ocean going vessels. In 2014, world container ship traffic carried more than 1.6 billion metric tons of cargo. Products shipped via container include a broad spectrum of consumer goods ranging from clothing and shoes to electronics and furniture, as well as perishable goods like produce and seafood. Containers also bring materials like plastic, paper and machinery to manufacturing facilities around the world.

In one year, a single large containership could carry over 200,000 containers. While vessels vary in size and carrying capacity, many liner ships can transport up to 8,000 containers of finished goods and products. Some ships are capable of carrying as many as 14,000 TEUs (twenty-foot equivalent units). It would require hundreds of freight aircraft, many miles of rail cars, and fleets of trucks to carry the goods that can fit on one large container ship. In fact, if all the containers from an 11,000 TEU ship were loaded onto a train, it would need to be 44 miles or 77 kilometers long.

Ocean shipping’s economies of scale, the mode’s comparatively low cost and its environmental efficiencies enable long distance trade that would not be feasible with costlier, less efficient means of transport. For example, the cost to transport a 20-foot container of medical equipment between Melbourne, Australia and Long Beach, California via container ship is approximately $2,700. The cost to move the same shipment using airfreight is more than $20,000.

As a major global enterprise, the international shipping industry directly employs hundreds of thousands of people and plays a crucial role in stimulating job creation and increasing gross domestic product in countries throughout the world. Moreover, as the lifeblood of global economic vitality, ocean shipping contributes significantly to international stability and security.

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WHY DO SHIPS FLOAT?

Ships float, even if they are made of iron, because their overall density is less than that of the water that supports them. The water displaced by the hull of the ship pushes back upwards with a force called up thrust or buoyancy. If this is equal to or greater than the force of gravity pulling the ship’s mass downwards, the vessel will float. In fact, ships need a certain amount of weight to give them stability in the water, so many of them have hulls weighted with concrete or another kind of ballast. Without it, the ship would bob around on the water like a cork.

Not such a silly question! A ship or a boat (we’ll call them all boats from now on) is a vehicle that can float and move on the ocean, a river, or some other watery place, either through its own power or using power from the elements (wind, waves, or Sun). Most boats move partly through and partly above water but some (notably hovercraft and hydrofoils) lift up and speed over it while others (submarines and submersibles, which are small submarines) go entirely under it. These sound like quite pedantic distinctions, but they turn out to be very important—as we’ll see in a moment.

All boats can float, but floating is more complex and confusing than it sounds and its best discussed through a scientific concept called buoyancy, which is the force that causes floating. Any object will either float or sink in water depending on its density (how much a certain volume of it weighs). If it’s denser than water, it will usually sink; if it’s less dense, it will float. It doesn’t matter how big or small the object is: a gold ring will sink in water, while a piece of plastic as big as a football field will float. The basic rule is that an object will sink if it weighs more than exactly the same volume of water. But that doesn’t really explain why an aircraft carrier (made from dense metal) can float.

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HOW DOES A TELEPHONE WORK?

A telephone works by sending and receiving electrical signals that represent sounds, including the human voice. When the required number is dialled, a signal passes to the called telephone, causing it to ring, buzz, flash a light, or even vibrate to attract the attention of the person using it. When the telephone is picked up or switched on, a connection is made, and a conversation can take place.

Messages reach the right telephone by means of a dialled number. Pressing the keys of the telephone causes different electrical pulses or varying tones to pass to electronic equipment at the telephone exchange. This “reads” the pulses or tones and routes the call to the correct area and telephone.

The Transmitter of a telephone serves as a sensitive “electric ear.” It lies behind the mouthpiece of the phone. Like the human ear, the transmitter has an 14 eardrum.” The eardrum of the telephone is a thin, round metal disk called a diaphragm. When a person talks into the telephone, the sound waves strike the diaphragm and make it vibrate. The diaphragm vibrates at various speeds, depending on the variations in air pressure caused by the varying tones of the speaker’s voice.

Behind the diaphragm lies a small cup filled with tiny grains of carbon. The diaphragm presses against these carbon grains. Low voltage electric current travels through the grains. This current comes from batteries at the telephone company. The pressure on the carbon grains varies as sound waves make the diaphragm vibrate. A loud sound causes the sound waves to push hard on the diaphragm. In turn, the diaphragm presses the grains tightly together. This action makes it easier for the electric current to travel through, and a large amount of electricity flows through the grains. When the sound is soft, the sound waves push lightly on the diaphragm. In turn, the diaphragm puts only a light pressure on the carbon grains. The grains are pressed together loosely. This makes it harder for the electric current to pass through them, and less current flows through the grains.

Thus, the pattern of the sound waves determines the pressure on the diaphragm. This pressure, in turn, regulates the pressure on the carbon grains. The crowded or loose grains cause the electric current to become stronger or weaker. The current copies the pattern of the sound waves and travels over a telephone wire to the receiver of another telephone. For more modern phones that have a telephone answering service, the sound wave is captured on a recording device which allows for the operator of the phone to playback at a later time.

The Receiver serves as an “electric mouth.” Like a human voice, it has “vocal cords.” The vocal cords of the receiver are a diaphragm. Two magnets located at the edge of the diaphragm cause it to vibrate. One of the magnets is a permanent magnet that constantly holds the diaphragm close to it. The other magnet is an electromagnet. It consists of a piece of iron with a coil of wire wound around it. When an electric current passes through the coil, the iron core becomes magnetized. The diaphragm is pulled toward the iron core and away from the permanent magnet. The pull of the electromagnet varies between strong and weak, depending on the variations in the current. Thus, the electromagnet controls the vibrations of the diaphragm in the receiver.

The electric current passing through the electromagnet becomes stronger or weaker according to the loud or soft sounds. This action causes the diaphragm to vibrate according to the speaker’s speech pattern. As the diaphragm moves in and out, it pulls and pushes the air in front of it. The pressure on the air sets up sound waves that are the same as the ones sent into the transmitter. The sound waves strike the ear of the listener and he hears the words of the speaker.

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WHAT IS SEMAPHORE?

Semaphore is a means of signalling using pairs of flags. Different flag positions stand for different letters and numbers. Semaphore signals are useful when the signaller is within sight of the receiver of the message but too far away to call out. It was widely used between ships sailing near each other in the days before ship-to-ship radio.

In programming, especially in UNIX systems, semaphores are a technique for coordinating or synchronizing activities in which multiple processes compete for the same operating system resources. A semaphore is a value in a designated place in operating system (or Kernel) storage that each process can check and then change. Depending on the value that is found, the process can use the resource or will find that it is already in use and must wait for some period before trying again. Semaphores can be binary (0 or 1) or can have additional values. Typically, a process using semaphores checks the value and then, if it using the resource, changes the value to reflect this so that subsequent semaphore users will know to wait.

Semaphores are commonly used for two purposes: to share a common memory space and to share access to files. Semaphores are one of the techniques for interprocess communication (IPC). The C programming language provides a set of interfaces or “functions” for managing semaphores.

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