My Science School

Basic radar equipment consists of a transmitter to generate the radio signals, a revolving scanner – the aerial or antenna that sends out and receives the signals – and a video screen on which the returning signals are displayed. The radio signals are transmitted as pulses (short bursts) at microwave frequencies, which are between 1000 and 35,000 million cycles per second. By comparison., the sound waves from a bar’s signals have frequencies of 30-120 thousand cycles per second.

Radar pulses are timed to allow one signal to hit its target and bounce back before the next one is emitted. Because radio waves travel at the speed of light, about 186,300 miles (300,000km) a second, pulse timing is measured in micro-seconds – millionths of a second. By measuring the time a signal takes to return, the distance to the target can be calculated.

If the object is moving, the returning signal has a slightly different frequency from the outgoing one. This is known as the Dolpher shift, and is caused by the radio waves bunching up if the objects approaching, or stretching out if it is going away. From this shift, radar operators can distinguish a moving object from a stationary one (such as a mountain) and can work out the direction in which it is travelling. From the size of the shift,m they can also calculate the speed. Radar microwave beams from orbiting spacecraft or satellites respond differently to the conditions they encounter – dense forests or cultivated fields, for example. Computers analyse the differing strengths of the return signals and build up picture of the surface.

 

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Bats navigate by emitting shrill squeaks that are reflected back to their ears from insect prey or obstacles in their path. Radar works in a similar way, but uses reflected radio signals to detect object up to 2000 miles (over 3200 km) away. Without radar, complex air-traffic control and missile early warning systems would be impossible to operate, and ships at sea would risk collision in the dark or in fog.

Radar devices its name from the term ‘Radio detection and ranging’. It was first developed in Europe and America in the 1930s, after the Italian engineer Guglielmo Marconi (the pioneer of radio) suggested the idea in 1922.

The French liner Normandie – which in 1935 set the Atlantic crossing record in just over four days – was fitted with radar in 1936, for detecting icebergs. By 1939 Britain, thanks to the work of physicist Sir Robert Watson-Watt, had a radar network on its south and south-east coast for detecting aircraft. The system proved invaluable to the country’s defences during the Battle of Britain in 1940. It had a range of about 40 miles (64 km), and operated day and night, passing the range, bearing and height of German planes to the RAF defence network.

Modern radar is sensitive enough to locate all the aircraft coming into a busy airport and allow air-traffic controllers to stack them at different heights in the sky while they organise a landing rota. Airliners are fitted with a radar beacon or transponder (transmitter-responder) on the underside. This sends their radar signals to the ground and back to give the pilot his altitude, and reflects signals from the airport’s two radar systems. The primary system gives warning of the aircraft’s approach and distance, and the secondary system sends coded signals to the transponder, which gives back the aircraft’s identity and height.

Radar signals can also be reflected from raindrops. Weather forecasters use radar networks to locate rain and snow clouds. Airliners have nose-mounted radar scanners that give the pilot a map of the weather up to 200 miles (320 km) ahead, so that he can avoid storms. In case of necessity, the pilot can tilt the scanner to get a rough map of the ground below.

Spacecraft and satellites orbiting the Earth use radar beams to gather information about the Earth’s surface for map-makers, geologists and oceanographers. Radar is also used to find out about the surfaces of other planets.

 

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Some toothpastes have the fluoride or mouthwash incorporated as a stripe.

The standard cleaning mixture is usually chalky white, while the fluoride or mouthwash is often a clear blue or red gel. The two pastes are mixed separately. As with all toothpastes, the empty tubes, called blanks, are filled from the wide end, which is then crimped and sealed. The two pastes contain colours that will not mix, so the pastes so not flow into one another. When the toothpaste is squeezed out of its tube, white and coloured stripes emerge.

 

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People who cleaned their teeth in the 1840s probably used one of various brands of toothpowder which contained ground-up coral, cuttlefish bone, burnt eggshells or porcelain. The powder might have been coloured purple with cochineal, derived from the bodies of tropical scale insects.

Today’s toothpastes – white, coloured or striped – contain ten or more ingredients. Some play a part in cleaning or protecting the teeth; some make the paste tastier; some bind the paste together; other help it a flow out of the tube.

The main ingredient in the white part of toothpaste is finely powdered chalk (calcium carbonate), or another mineral powder such as aluminium oxide, which is an slightly abrasive and help to remove the dulling film which is deposited by food and drink and contains decay-causing plaque.

Some titanium oxide, a white powder, is sometimes also added to whiten the toothpaste.

Clear gel toothpastes get their abrasive quality from transplant compounds of silica, often with a colouring added.

The cleaning and polishing ingredients are combined with water into a thick paste by the addition of a binding and thickening agent such as alginate, which is derived from seaweed.

A trace of detergent is added to create foam and help the cleaning process. to make the paste palatable, it is usually sweetened with peppermint oil and menthol.

A moisturizer such as glycerin is also added to prevent the paste from drying out. In addition most toothpastes now contain fluoride which helps to strengthen tooth enamel. Disinfectant such as formalin may also be included to kill bacteria.

 

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In 1861 the firm of Bryant & May produced their first safety match at a factory at Bow, East London. By the end of its first year the factory was turning out 1,800,000 matches a week. They were so much in demand that in 1871 the Chancellor of the Exchequer proposed a ‘match tax’ of a penny a box. The proposal caused an outcry in Parliament and the Press – and thousands of match workers protested at what they saw as a threat to their livelihood. Riots resulted, and so Parliament abolished the levy.

Throughout the world matchmaking techniques became more streamlined until today more than 800 boxes of matches can be made every minute.

 

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To make a pencil lead, graphite is mixed with fine clay – the soft that is used in the finest porcelain and bone china. The two ingredients are combined in different proportions to produce leads of different blackness and hardness.

The most widely used type of pencil is the HB (hard and black). Softer and blacker pencils (B and BB) have more graphite, and harder ones – graded from H (hard) to 10H – have progressively more clay.

The leads for coloured pencils or crayons contain no graphite at all. They are made from pure clay and wax, coloured with pigments.

 

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