Category Science

How is an automobile’s speed measured?

          An automobile’s speed is measured by a speedometer fitted next to the steering wheel of a car. It indicates the vehicle’s speed in kilometers per hour or miles per hour. The speed is read on the dial which is numbered from 0 to 160, by means of a pointer. Most speedometers also incorporate an odometer – a device that records the distance travelled by the vehicle.

          A speedometer is driven by a flexible cable that is connected to a set of gears in the vehicle’s transmission. When the vehicle moves, the gears turn a core or flexible metal shaft inside the cable. The core turns a magnet inside a metal drum called a speed cup. This is located inside the speedometer housing. The revolving magnet exerts a turning force on the speed cup. In turn the speed cup is held back from revolving freely with the magnet, by the opposing action of a hairspring. The movement of the speed cup is transferred to the pointer on the dial. The hairspring brings the pointer back to ‘zero’ when the vehicle stops moving. Most of the speedometers register 36 km/hr when the core inside the cable revolves at 1000 revolutions per minute.

          The odometer registers total kilometers travelled by the vehicle. Some automobiles also have Trip odometers that can be reset to ‘zero’ at the beginning of a particular trip. An odometer consists of a chain of gears (with a gear ratio of 1000 : 1) that causes a drum, graduated in 10th of a mile or kilometer, to make one turn per mile or kilometer. A series, commonly of six such drums, is arranged in such a way that one of the numerals on each drum is visible in a rectangular window. The drums are coupled so that 10 revolutions of the first cause one revolution of the second and so forth, the numbers appearing in the window represent the accumulated mileage.

How is electricity conducted through wires?

Electricity is supplied to our homes, schools, factories and stores through copper or aluminium wires from power stations. These power stations burn coal or oil, use nuclear reactions or the energy of falling water to produce energy to run the generators. The power thus generated is then transmitted to different cities and places where it is required. Electricity is then transmitted through transmission lines.

To avoid the loss of power, the output voltage from the generator is first stepped up to a high voltage by a step-up transformer. After being received at the city power station, it is again reduced to low voltage, before it reaches our homes or factories. Now question arises how is electricity conducted through wires?

We know that all substances are made up of atoms. Materials which allow the passage of electricity are called conductors. Metals, such as copper, aluminium, silver and gold are good conductors of electricity. The atoms of these metals have loosely bonded electrons. These electrons are free to move within the metal. These are called free electrons and are responsible for the conduction of current. More the number of free electrons in the metal, better it conducts the electricity. 

When electric battery is connected across the ends of the metal wire, the negatively charged free electrons move away from the end connected to the negative terminals and flow toward the positive terminal. This flow of electrons is nothing but the electric current. Hence the drifting electrons cause electricity to flow. Greater the number of free electrons in a metal, easier it is for electricity to flow through it.

Some materials are poor conductors of electricity because they have less number of free electrons. Poor conductors resist the flow of electricity. The resistance of a wire depends upon its material length and area of its cross-section.

Some substances do not allow electricity to flow through them and are called insulators. These substances contain tightly-bonded electrons that cannot move away from atoms. Hence they do not conduct electricity. Glass, mica, wood, plastic and rubber are common insulators. Some substances like silicon and germanium are neither good conductors nor insulators. They are called semi-conductors. 

How does an automobile engine work?

          An automobile such as a car is an automatic self-propelled vehicle. It runs on a gasoline, diesel or electric engine. Petrol or diesel engines used in automobiles are internal combustion engines. In these engines, fuel burns in the cylinder. In an electric engine, there is a motor and a gear box. It is battery-powered and used for small cars on a limited and experimental basis.

          Petrol engine is used in most automobiles. However, some automobiles even use diesel engines. Diesel engines are heavier and more expensive than gasoline engines, but they last longer and use less refined fuel.

         Both the petrol and diesel engines are four stroke engines. Their construction and working can be understood as follows:

Petrol Engine: It consists of a cylinder containing an air-tight piston. It is connected with the main shaft through a crank by means of a connecting rod. As the piston moves to and fro, its motion is converted into rotational motion of the crank shaft. The cylinder has two valves: one inlet valve and the other, exhaust or outlet valve. Inlet and outlet valves open and close automatically only once in every cycle. Air is mixed with petrol vapour in a carburetor and is made to pass into the cylinder through the inlet valve. The mixture is burnt in the upper portion by means of an electric spark provided by the spark plug. The action of the engine may be explained in four strokes.

          When the engine is made to work at the beginning by external force, the inlet valve opens and the mixture of petrol vapour and air is allowed into the cylinder. This is known as the charging stroke. Now both inlet and outlet valves close and the fuel mixture is compressed. This is known as compression stroke. The spark plug produces an electric spark and causes the mixture to burn. Due to combustion of the fuel, a large amount of heat is produced. This gives rise to heavy pressure and as a result the piston moves. With the movement of the piston the vehicle moves. This is known as the working or power stroke. Finally the exhaust valve opens, but the inlet valve remains closed. Unused gases, left at the end of the working stroke are thrown out. This is known as the exhaust stroke. In this way, one cycle is over. As the process is repeated, the vehicle goes on moving.

          Most automobile engines have four, six or eight cylinders. Most of the engines are in the front and drive the rear wheels. 

Continue reading “How does an automobile engine work?”

What is a periscope?

         A periscope is a very useful and interesting optical instrument. It enables officers aboard a submerged submarine to observe whatever might be happening on the surface. A submarine’s periscope can move up and down and turn to look in a complete circle. It allows tank commanders to view the battlefield from inside their armoured vehicles. It is therefore, useful in land and sea warfare. Now let us see what exactly a periscope is.

          A periscope is an optical instrument with which a person can see around corners and other obstructions. This instrument is based upon the principle of reflection of light from two parallel mirrors. A simple periscope consists of a long tube bent twice at right angles. Two plane mirrors, parallel to each other, are fixed in such a way, that the reflecting surfaces of the two mirrors make an angle of 45° with the axis of the tube. Rays coming from an object in front of the periscope, after undergoing two successive reflections, reach the eye of the observer thus enabling him to see the object.

         Some sophisticated periscopes also make use of reflecting prisms and magnifying optics, which make distant objects, appear closer. They are also fitted with devices for estimating the range of the target. Objects can be photographed through a periscope.

          Simple periscopes, made of cardboard, are also popular among spectators at parades and sporting events. With its help, they can see above people’s heads!

          Periscopes are also used in industry to observe nuclear reactions and the interiors of special furnaces and other dangerous devices.

          The longest periscope in the world measures 27 m. It is located at the National Reactor Testing in Idaho Falls, Idaho. It is used to view nuclear reactor operations.

How are hard drinks made?

          Wine is probably the first type of hard drink to have come into existence. Archaeological evidence suggests that wine making began in the middle-east over 10,000 years ago, and gradually spread westward to the mediterranean countries and finally into Europe. The ancient Egyptian wall paintings reveal that the art of wine making was known to them long before the Westerners took to it.

          Wine was common in everyday life of the early Greeks and Romans. It also played an important role in their religious ceremonies. The God of wine was called Bacchus by the Romans and Dionysus by the Greeks.

          Wine can be made from a wide range of fruits and vegetables, but the real wine is made from grapes. Grape juice contains water, sugar, fruit acids and many trace elements. The outer grape skin has millions of tiny living organisms, primarily yeasts, including a number of moulds and bacteria, too. 

          The grapes are allowed to ripen until they attain suitable sugar content (18% or more) and acidity. When these grapes are crushed, yeasts come into contact with the juice. This brings about the process of fermentation by which grape juice changes into alcohol and carbon dioxide. During fermentation, grape juice loses its sugar and turns into wine. This wine has 10 to 14% alcohol content. The rest of wine consists of water containing traces of acids, sugar and other substances which give the wine its colour and flavour.

          Another type of hard drink, beer, is known to have been made by the Egyptians and Babylonians at least 6000 years ago and there is evidence that barley, from which it is made, was cultivated in Britain and northern Europe, some 5000 years ago. Europeans knew how to produce a fermented drink from barley. Beer is usually made from barley hops, yeast and sugar by the process of fermentation.

          Pure brandy is made by the distillation of wine made from grape juice. The wine is heated and the alcohol that evaporates out of it is condensed and collected. Apart from alcohol, other substances are also given off during distillation. Some are poisonous substances and are removed.

          Different types of whisky are made from grains such as barley, rye and corn. Rum is made from molasses, syrup obtained from cane sugar. Gin is made from grain or molasses flavoured with juniper berries.

          Major wine-producing areas of the world include France, Germany, Spain, Portugal, Italy and California in the USA. 

How are matches made?

            When a strip of wood, cardboard or waxed paper tipped with a chemical mixture is rubbed against a rough surface, the chemicals burst into a flame and produce fire. The first match was made in 1827 by an English pharmacist John Walker. It was a splint of wood tipped with antimony sulphide, potassium chlorate, gum arabic and starch. The match bursts into flames with a series of small explosions that showered the experimenter with sparks. The first safety match was invented in 1844 by a Swedish chemist Gustave E. Pasch. Let us discuss how matches are made?

            Red phosphorous is the main substance used in the match industry. Matches are mainly of two types: Lucifer or friction matches and Safety matches. 

            Lucifer or friction matches light when rubbed against any rough surface. The match is basically a wood splint or shaft about 8 cm long and 0.3 cm in diameter. It may have a tip of two colours, red and white or blue and white. One-fourth of the wooden strip is first dipped in molten sulphur or paraffin wax. The small white tip is made from the paste of phosphorous trisulphide. Other substances are antimony trisulphide (kindling material), potassium chlorate (supporter of combustion), powder of glass or silica (friction producing substance) and gum or glue (to act as a binder). Red or blue part of the tip does not ignite by rubbing, but burns when the white tip has caught fire. It carries the flame to the rest of the match stick. These matches are made by machines which produce millions of matches per hour.

            Nowadays only safety matches are used. Safety matches can only be ignited by striking them against a special surface. The surface is usually located on the sides of the match box. The tip of the safety match is made from the substances mentioned above except phosphorous trisulphide. Red phosphorous is used as the igniter in place of phosphorous trisulphide. When the head of the match stick moves over the rough surface, the molecules in the head and the surface collide with each other and the head of the match becomes hotter. The substances in the head become hot enough and make the head burst into a flame. These matches generally do not light when struck on any other surface. The chances of such a match stick catching fire accidentally are thus eliminated.