Category Everyday Science

Most drivers have experienced the frightening moment when the wheels lock and the car slides uncontrollably toward the vehicle in front. Although drivers ate taught to leave a sufficient gap for braking, and to take extra care on wet or icy roads, the huge number of rear-end collisions every year is ample evidence they do not.

Skidding and sliding happen because the behaviour of a car changes rapidly when the wheels begin to lock. Up to a point, pressing the brake pedal harder produces greater deceleration. But once the wheels have locked, their grip on the road is lost, they begin to slide instead of turn, and the driver can no longer control the car’s direction. Panic follows, and the natural reaction is to stamp ever harder on the brake, which makes things worse.

Advanced driving manuals recommend cadence braking, in which the brake pedal is pumped up and down in quick succession to ensure that the wheels never lock. But, in practice, few drivers have the skill or experience to do this in an emergency.

Anti-lock brakes are designed to auto-mate the technique of cadence braking, taking the skill out of the hands and feet of the driver and entrusting it to a package of electronics and hydraulics. They consist of two parts: an electronic sensor that can detect how rapidly the wheels are decelerating, and a system for automatically controlling the hydraulic pressure on the brakes to achieve the best and safest deceleration.

The sensor consists of a slotted or toothed exciter disc attached to an axle or inside a brake drum. As the axle turns, each tooth and gap in this disc pass close to a monitor and generate a current, which varies according to the rate at which the disc is rotating.

The signals are interpreted by electronic circuits, which determine both the speed of the disc and the rate at which it is decelerating. If the disc is slowing down too rapidly and is about to lock, the circuits instruct the hydraulic controls to reduce brake pressure, preventing a skid. As the driver continues to press the brakes, pressure rises again, and the system repeats the operation until the vehicle has stopped. The system can produce up to 45 cadences a second, if required.

The details of how the electronic signals are used to control brake pressure depend on individual designs. Some of earliest non-skid brakes, in the 1960s, were fitted to trucks, which use air under pressure to activate their brakes. In these systems it is relatively simple to bleed off some of the air through a valve to reduce pressure. The air lost can easily be replaced by drawing on air stored under pressure in the vehicle.

The same simple arrangement cannot be applied to cars, which use hydraulic fluid. This is because there is little fluid in reserve, and also it would be both expensive and dangerous to spill bled-off hydraulic fluid all over the road. One alternative is to reduce pressure by briefly increasing the volume of the hydraulic system — with a piston arrangement, for example — and then to restore pressure again. Among the systems that have been developed are some that even allow sharp turns to take place safely during heavy braking.

Although anti-locking brakes were originally available only on the most expensive cars, they are increasingly becoming standard, or optional, on most new cars.

 

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The Czech playwright Karel Capek introduced the name robot in the early 1920s. He wrote a play called Rossum’s Universal Robots in which an army of industrial robots became so clever that they took over the world. Capek coined the word robot from the Czech robota, which means ‘slavery’. Since then men have worried not so much about robots taking over the world, but more about robots taking over their jobs.

Robots have indeed taken over some jobs — dull, mechanical, routine work. They save costs because there is no need for them to change shifts, they do not tire or lose concentration, they do not take tea or coffee breaks, they do not fall ill (although they may need repairs), and they do not go on strike. But even though American and British researchers have produced robotic four-fingered hands capable of picking a flower, robots are still a long way from having the perception, dexterity or flexibility of human beings.

 It is, however, generally accepted that the responsible use of robots in industry is beneficial because it saves people from doing dull and dangerous jobs. Robots were used to clear up the radioactive debris after the Three Mile Island nuclear accident in America in 1979. They are also being developed for inspecting and manufacturing nuclear plants, fighting fires, Felling forest trees, and acting as security guards — walking burglar alarms that can warn human guards of an intruder. And I four-legged, 72 ton robot was used to roll boulders to build up the sea wall in Tokyo Bay, Japan, in 1986 — saving 50 divers from the risky task.

Experiments are also under way with robots that can help infirm and disabled people to be independent. Researchers in Britain and America are developing robots that can respond to spoken commands. They will be able to undertake such tasks as brushing teeth, serving soup, loading a computer, opening filing cabinets and picking up mail.

 

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American motorists were able to buy petrol with oil company credit cards before the First World War, but the age of the credit card dawned in 1950 with the introduction of the Diners Club charge card by American businessman Frank McNamara. The idea came to him after dining in a New York restaurant and discovering he had mislaid his wallet. The Diners Club card is not strictly a credit card because the whole bill has to be paid when the invoice is received — most other cards carry forward a debit balance.

Today there are more than 350 million credit or charge cards in use in the United States alone. Worldwide, cards are numbered in billions.

Smart cards are likely to have a wider use than for money transactions. in the late 1980s some medical authorities in parts of Europe, the USA and Japan began trials with medical identity cards —smart cards carrying the holder’s medical history. The cards save time and paperwork, as they can be consulted by doctors and chemists in computer terminals at hospitals, surgeries and pharmacies, and updated each time the patient is seen. The European trial programmes aim to produce a standardized EEC care or health smart card for use in the 1990s.

Also available are laser cards, developed in the USA, in California. They are not as smart as smart cards, but are able to carry a much larger store of personal information, contained in a pattern of tiny holes — only a thousandth of a millimetre across — on a photosensitive strip. The dots, like the pits and flats on a compact disc, can he read by a laser scanner in a special terminal.

The card can hold coded identification details, including fingerprints, signature, voice print, and even a photograph,’ as well as various hidden security codes making it -virtually impossible to counterfeit Its information storage space is so vast there is plenty room for such things as bank accounts, medical history and educational attainments. Information is filed on the card under separate access codes, so the bank, for example, could read out only financial information and the doctor only medical information.

 

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Every successful shopkeeper needs to know which goods are selling well and which are going slowly, so that he can restock or phase them out, as appropriate. For the small shop, tidy bookkeeping and a glance at the shelves may give all the information necessary. But supermarkets and other big stores need quick and accurate records of a much larger flow of merchandise. That is why they use bar codes, which are printed on the packaging.

A bar code can be read by a laser scanner, which passes it to a computer. This supplies the details and price of the goods, records the sale for storekeeping, totals the bill, and feeds the information to the cash register which prints out a receipt.

Common bar codes are European Article Numbers (EAN), based on a number with 13 digits, and Universal Product Code (UPC), based on a number with 12 digits. The Australian Product Number (APN) is also based on 13 digits. Each digit is represented by a series of parallel straight lines and white spaces. The laser scanner translates the information into binary digit signals, which it feeds to the computer.

The code gives the manufacturer details of the product and the package size, and includes a security code that prevents anyone altering it or the scanner misreading it. The computer supplies the price from the product information. So the only way to change the price of an item is by altering it in the computer.

 A laser scans a bar code with a beam of light passed from one end to the other. It is sensitive enough to read from left to right or right to left. Although the bar codes are usually printed in black on a white background, a laser can read a bar code which is printed in any dark colour except red, and the background can be any pale or pastel colour. Some of the lasers used scan with red light, so cannot pick up a reflection from red.

Bar coding is faster and more accurate than other systems. Human error is limited because staff do not have to mark a price on every item, and checkout assistants do not have to key in prices at the register. However, because the computer sup-plies the prices at the checkout, the store management has to ensure that the goods on the shelves display the same prices. Also that the shelf price is changed if a computer price is altered, or a customer may appear to he charged the wrong price.

 

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Chips are produced several hundred at a time on a slice of ultra pure, artificially formed silicon crystal, so thin that it would take about 250 slices to form a piece 1in (25mm)thick. Layout diagrams for circuits are prepared on a computer, then each reduced to chip size and set out side by side on a glass plate known as a mask. Because witches and other components are built up in separate layers on the chip, a mask is made for each operation. The masks – which block out the unwanted parts – are made many times larger than the chip and reduced photographically.

The chips are built up by forming each layer – p-type or n-type layers or insulating layers of silicon dioxide – and etching out the unwanted parts. This is done by treating the layer with a coating sensitive to ultraviolet light, masking it, then exposing it to ultraviolet light. The exposed parts become resistant to acid, but the blocked-out parts do not – they are etched away when the layer is coated with acid.

Parts such as aluminium contacts are deposited in the areas etched for them as a vapour. When hardened, the aluminium is etched to add the required circuit connections, which lead to contact pads at the edges of the chip.

All completed chips on slice are tested with delicate electrical probes to check that they are working properly. About 70 per cent prove faulty. They are marked as rejects and thrown away. After testing, the slice is cut into individual chips under a microscope with a diamond-tipped cutter. The good chips are each mounted in a frame that is encased in plastic. The contact pads are linked to metal connectors are in turn linked to protruding legs, or pins, that plug into the external circuit.

 

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Transistors are the commonest components in a microchip. They are used mostly as switches, letting current through to represent the binary digit 1, or cutting it off to represent 0.

A widely used type of transistor has two islands of n-type semiconductor in a larger base of p-type. While the transistor is switched off. The free electrons from the layers drain into the p layer and are absorbed by the free holes. The transistor is switched on by applying a voltage from a separate low-power circuit to an aluminium gate above the p base. This voltage attracts the free electrons from the p base towards the gate. They then form a bridge between the two n islands and provide a path for the current through the circuit in which the switch is operating.

The transistor is switched off by cutting off the power. The free electrons then drain back to the p base and are absorbed by the free holes. Without the bridge they formed between the islands, current cannot flow through the circuit.

 

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