Category Science

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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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.

Picture Credit : Google

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.