How does welding work?

Welding is a method that permanently joins two pieces of metal. Heat is applied to two of the metal edges or surfaces, usually with a gas torch or electric welding tool.

However, when large surfaces are to be welded, large machines are used. The heat applied by the machines melts the two surfaces or edges until they melt into one piece.

During the welding process, the heated metal must be protected from oxygen and nitrogen in the air, as these gases cause the weld to be weak and brittle. This protection is provided by spraying other gases into the metal during the welding process.

Once the two pieces of metal are welded together and the weld cools and hardens, the assembly is as strong as any other part of the metal. Welding is used in the manufacture of cars, buildings, bridges, airplanes, and large electrical appliances.

The heat generated by welding is often more than 1,500° Celsius.

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What makes a boat float?

According to Newton's law of gravity, each object exerts an attraction on the things around it. Since the Earth is millions of times bigger than the things on it, everything pulls it towards itself. If it were not so, everything on Earth, including people, would be shot into space.

Why, then, when a ship is on the water, does it not sink? After all, its structure, machinery, cargo, crew and passengers add up to a weight of thousands and thousands of tons.

The reason is that all ships have been designed with hollow areas that are filled with air. And while a ship pushes some of the water to the sides when it floats, the large amounts of air inside weigh less than the water that is displaced. The water beneath it, however, weighs much more and pushes the ship up, which makes it float.

Examples of buoyancy can be seen in beach balls, if one pushes the ball into the water, it reacts by pushing the ball up.

What determines whether an object floats or sinks is its density, the amount of air inside it. A large piece of wood floats, because the air fills many of its spaces, but a small stone will sink because it has a greater density, with no air inside.

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Why does a balloon filled with helium rise?

A balloon rises because it has buoyancy, a lifting power that gives it the gas inside. Some gases are heavier than air and some are lighter.

It is only when a balloon is filled with a gas lighter than the air that it will begin to rise. The most common gas to fill balloons is helium.

A balloon filled with helium will remain suspended in the air as long as the gas inside and the equipment that is attached to it (basket, ropes, etc.) weigh less than the air in which they are floating.

The balloon will rise to a height, where the weight of the air outside the balloon is in balance with the weight of the air inside it. At that moment, it begins to float.

Gradually, however, the gas inside begins to escape and the balloon begins to descend to the ground.

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How does a satellite TV work?

Communications satellites launched by giant rockets have been in orbit around the Earth since the 1960s. On board each satellite is a radio receiver to receive signals from Earth, an amplifier to reinforce these signals, and a transmitter to send them back to Earth. All this electronic equipment is powered by solar batteries.

Television, radio, Internet and telephone conversations can be transmitted from one part of the Earth to another through any of the various communications satellites currently orbiting. A single satellite can receive and transmit thousands of telephone conversations and many television programmes all at the same time.

If, for example, the Wimbledon Tennis Tournament Championship is broadcast all over the world from England, that signal is sent from a transmitting station in England to three satellites in orbit: one over the Atlantic Ocean, another over the Indian Ocean, and the last over the Pacific Ocean. Both the land stations that send and receive the signals must point their antennas directly to the satellite so that the signal is transmitted clearly.
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How does a periscope work?

A periscope is constructed and functions similarly to a telescope, with a long tube containing a mirror at each end. The mirrors are mounted on the tube so that they are parallel to each other at a 45° angle to the axis or imaginary centerline of the tube.

In more advanced periscopes, additional lenses have been added to enlarge the image. Underwater periscopes are even more complicated. They have reflective prisms on the top and bottom of the tube, with two telescopes and several lenses between the two ends, and an eyepiece on the observer's side. The underwater periscope also has a thick, rigid waterproof cover and can withstand water pressure at great depths.

In addition to submarines, war tanks also use periscopes to search for enemy targets. Both vehicles have a periscope that can be raised or lowered, as well as turned in a 360° circle.

Periscopes can also be built so that they see around corners!

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