IELTS Academic Reading Practice Test 164

For more than six centuries, rockets were powered by solid mixtures. The gunpowder devices that Chinese makers launched at festivals, and the iron-cased rockets that Indian armies fired at British troops in the 1790s, depended on fuel that burned until nothing remained. A solid motor cannot easily be throttled, stopped or restarted, and its casing must withstand the full pressure of combustion throughout the burn. Nineteenth-century engineers improved the charges and the nozzles, but the energy released by a given mass of propellant stayed modest, and there was no practical way to control it in flight.

The first person to work out how rockets might escape these limits was Konstantin Tsiolkovsky, a Russian schoolteacher. In an article published in 1903 he argued that a rocket driven by liquid propellants would be far more powerful than one burning gunpowder, and he identified liquid oxygen and liquid hydrogen as the most promising combination. He also set out the mathematics relating the speed a rocket can reach to the speed of its exhaust and to the proportion of its mass given over to fuel. Tsiolkovsky was a theorist, however: he never built or tested a liquid-fuelled engine.

Similar ideas were reaching the United States. Robert Goddard, a physicist at Clark University in Massachusetts, had experimented with solid-fuel rockets since his student days. A pamphlet he published in 1919, A Method of Reaching Extreme Altitudes, examined what a rocket might do beyond the atmosphere and discussed liquid hydrogen and liquid oxygen as possible propellants. The suggestion that a rocket could one day reach the Moon attracted ridicule in the newspapers, and Goddard was stung by it.

On 16 March 1926, on his aunt's farm at Auburn, Massachusetts, Goddard launched the first rocket to be powered by liquid propellants. It was a spindly machine about three metres tall, with the engine at the top and the tanks below, and it burned liquid oxygen with gasoline. The propellants were forced into the combustion chamber by pressure from a gas supply rather than by pumps. The flight lasted two and a half seconds, and the rocket rose about 12.5 metres before coming down 56 metres away in a cabbage field.

Later rockets grew steadily more capable. Goddard added a gyroscope to steer them, vanes in the exhaust to correct their course, and pumps able to deliver large quantities of propellant. In July 1929 he flew a rocket carrying a camera, a barometer and a thermometer, the first such instruments to fly in a liquid-fuelled rocket. Because he feared that rivals would steal his designs, he worked in near-secrecy, and his achievements were slower to influence others than they might have been.

In Europe the idea was taken up by enthusiasts rather than by a single inventor. Hermann Oberth, a German-speaking teacher from Transylvania, published a book in 1923 with the uncompromising title Die Rakete zu den Planetenraumen (The Rocket into Planetary Space). It sold well enough to inspire a generation of experimenters, and amateur societies in Germany began testing small liquid-fuelled rockets in the late 1920s. The army, forbidden heavy artillery by the Treaty of Versailles, took a close interest.

The most consequential of these experiments produced a weapon. At the research station at Peenemunde on the Baltic coast, a team led by Wernher von Braun developed the A4, better known as the V-2. Its first fully successful flight, on 3 October 1942, reached a height of about 85 kilometres and came down about 190 kilometres away. The engine burned liquid oxygen with a mixture of ethanol and water, and turbopumps drove the propellants into the chamber at more than a hundred kilograms a second. The weapon was built by forced labour, and the rockets fired at Allied cities killed thousands of civilians.

After 1945 both the United States and the Soviet Union recruited German engineers and copied their hardware, and the V-2 became the foundation on which two space programmes were built. The first intercontinental ballistic missile was also liquid-fuelled. The Soviet R-7, a two-stage vehicle burning liquid oxygen and kerosene, was tested in 1957, and on 4 October of that year a modified version carried Sputnik 1, a metal sphere barely half a metre across, into orbit. The same rocket family later launched the Vostok missions that carried the first cosmonauts.

The American response drew on the German engineers as well as on home-grown designs. The rocket that carried Explorer 1, the first United States satellite, into orbit on 31 January 1958 was a modified Redstone, a short-range military missile whose engine burned liquid oxygen and an alcohol-based fuel. In the early 1960s American engineers flew the first stage to be powered by liquid hydrogen, which gives the highest exhaust speed of any practical propellant but must be kept at about 20 degrees above absolute zero.

Liquid propulsion has dominated large rockets ever since, for reasons that Tsiolkovsky, Goddard and Oberth had all foreseen. A liquid engine can be throttled, shut down and restarted, which solid motors cannot readily do, and its propellants can be held in lightweight tanks that need not withstand the pressure of combustion. Solid motors survived because they are simple, cheap and always ready, which makes them well suited to military missiles and to the boosters strapped to the sides of a launcher. Almost every orbital launch today repeats the experiment of 1926.

Haptics is the branch of engineering that deals with touch. The term covers two rather different kinds of sensation. Kinesthetic feedback concerns the position and movement of the body: the resistance of a heavy door, the pull of a steering wheel, the weight of a tool. Tactile, or vibrotactile, feedback concerns what the skin itself feels - texture, vibration, a tap on the shoulder. The word comes from the Greek haptikos, meaning 'able to touch'. Today the most familiar haptic device is the phone in almost everyone's pocket, which buzzes to announce a message.

Designing touch sensations means designing for the skin, and the skin is a crowded sensorium. Four main types of mechanoreceptor, nerve endings that respond to mechanical deformation, lie at different depths and respond to different aspects of a stimulus. Pacinian corpuscles, deep in the tissue, are tuned to high-frequency vibration of roughly 200 to 300 hertz, the range in which a phone buzzes. Meissner corpuscles, closer to the surface, detect lower frequencies. Merkel cells respond to steady pressure, and Ruffini endings to stretching of the skin. The density of these receptors also varies: the fingertips can distinguish two points only a couple of millimetres apart, while the back cannot separate points several centimetres apart.

Most consumer devices create vibration with a tiny electric motor carrying an off-centre weight, an arrangement known as an eccentric rotating mass motor. As the weight spins, it pulls the motor off balance and the whole phone shakes. The design is cheap and proven, but it has drawbacks. The motor takes tens of milliseconds to reach full speed and as long again to stop, so a crisp click is impossible, and the frequency of the vibration is tied to the speed of rotation, so one motor produces essentially one note. The linear resonant actuator, which drives a small mass back and forth on a spring, is quicker and more efficient, but only when driven at its resonant frequency, typically between 150 and 200 hertz.

A third family of actuators uses piezoelectric materials, usually ceramics, which change shape when a voltage is applied to them. Because the deformation happens within microseconds and nothing has to spin up, piezoelectric actuators can produce the sharpest and most precisely timed taps, and they can be driven across a broad range of frequencies. Their disadvantages are practical: they need relatively high voltages and are more expensive to manufacture. Designers therefore choose between motors and ceramics according to whether a device needs subtle detail or simply a reliable buzz.

Making sense of these signals is a matter of timing. Perception research has shown that if a visual event and a tap arrive within about 50 milliseconds of one another, the brain treats them as simultaneous, and if the tap comes slightly later the two may be bound together into a single, more convincing impression of contact. Designers exploit this tolerance. A short, sharp signal is read as a click; a long, low one as a rumble. By varying frequency, amplitude and duration, and by placing signals carefully in relation to what appears on a screen, engineers can suggest textures and materials that are not physically there.

Force feedback, the kinesthetic branch, is more demanding, because the device must push back against the user rather than merely buzz. Surgical simulators use it so that trainees can feel the resistance of tissue as they practise cutting and stitching, and research systems add force sensing to robotic instruments so that a surgeon working at a console can tell how firmly a tool is pressing. Rehabilitation engineers build exoskeletons and gloves that guide a weakened hand through an exercise or resist it, and flight simulators reproduce the stiffening of the controls as an aircraft approaches the speed at which it will stall.

Car manufacturers have been enthusiastic adopters. As dashboards have replaced physical knobs with flat screens, drivers have to look away from the road to find controls, and a vibration under the fingertip can confirm that a control has been activated without a glance. Some systems go further, giving each function its own pattern, so that an experienced driver can recognise a temperature control, say, without reading the label.

The most striking recent development is haptics without contact. An array of ultrasonic loudspeakers can be arranged so that sound waves converge at a point in the air, creating a small region of high pressure that a hand feels as a puff, a point or a line. By moving the focus rapidly, a computer can draw shapes that seem to float in space, allowing a user to press a virtual button with no screen involved. Because the sound lies above the range of human hearing, the sensation arrives in silence.

The limitations of haptics are rarely mentioned in demonstrations. An actuator occupies space, adds weight and consumes battery power, all of which matter in a device designed to slip into a pocket. There is no agreed vocabulary of sensations, so a pattern that feels to its designer like a click may feel to a user like a fault. Many people switch vibration off altogether, because it drains the battery or interrupts them at inconvenient moments, and once it has been switched off it cannot carry information. Yet for someone who cannot see a screen or hear a warning tone, a well-designed pattern of taps can be the difference between a message received and a message missed.

Type the name of an obscure household object into a search engine and, for days afterwards, advertisements for that object will follow you around the internet. To most people this is at best tiresome and at worst sinister. The industry responsible prefers a different word: relevant. Both descriptions are accurate, and the argument that rages between them is so confused that it is worth separating two quite different questions that are usually bundled together: whether targeted advertising works, and whether the way it is bought and sold is acceptable.

The mechanics are simple enough. When a page loads, a piece of code notes the identifier stored on the visitor's device, matches it against a profile held in a database, and sends an offer to an exchange. There, in the few hundred milliseconds before the page finishes rendering, advertisers bid for the right to show a single advertisement. The winner's image appears and the profile is updated. This process, real-time bidding, handles the great majority of display advertising on the open web. The profile itself is assembled from browsing history, earlier purchases, approximate location and hundreds of other signals, which is why an advertisement for something you merely glanced at can follow you for a fortnight.

On the first question, the honest answer is that targeting does improve response, but by less than its advocates claim. Advertisers have known since the early days of direct mail that a message sent to a likely customer does better than one sent at random, and controlled trials of online campaigns generally confirm a modest advantage for behavioural targeting over simpler forms. What is far less clear is whether that advantage justifies the machinery required to obtain it. The gains are largest for products bought rarely and considered at length - a holiday, a car - and negligible for the everyday items that make up most advertising.

The second question is harder, and it is here that the industry's case is weakest. Even a modest browsing history permits inferences that the user never intended to disclose. A visit to a medical site, a search made late at night, a location tracked across a week: combined, these can suggest illness, financial difficulty, pregnancy or religious belief. Advertisers rarely need such details, but the systems that assemble the profiles do not distinguish between what is necessary and what is merely available, and the resulting dossiers are traded by firms the user has never heard of.

None of this would matter much if the economic case were overwhelming. It is often said that advertising pays for the free web, and to a considerable extent it does: newspapers, forums and reference sites depend on it. Yet the argument is used to close down discussion rather than to advance it. Free services existed before behavioural profiling and would exist after it; the real question is what kind of advertising would replace it, and which publishers would be paid. Advertisers also point out that advertising has always annoyed people, and that annoyance is a poor guide to harm.

Regulators have begun to answer that question in ways the industry dislikes. Under the European data protection rules that took effect in 2018, any use of personal data needs a legal justification, of which consent is merely one. The Digital Services Act, which began to apply in 2024, goes further: it prohibits advertising that uses sensitive categories of data, including information about health or religion, and bans the targeting of advertisements at children altogether. These are not bans on targeted advertising. They are limits on particular practices, and they rest on a defensible distinction - between using what a person does in order to choose which advertisement to show, and building a lasting dossier about who that person is.

The remedy most widely adopted, the consent banner, has been a failure. Users click 'accept' to make the banner disappear, rarely read the options and have little idea what they have agreed to. Consent was the wrong mechanism for a problem of this size: it places the burden on individuals who have neither the time nor the information to make a reasoned choice, and it produces a ritual that everyone performs and nobody means.

A better answer may be older than the problem. Contextual advertising chooses advertisements to match the content of a page rather than the history of its reader, and it needs no profile and no tracking. A holiday company can advertise beside a travel article; a maker of running shoes beside a report on a marathon. Advertisers have long dismissed context as crude, yet the evidence that it performs badly is thinner than the industry suggests, and it has one advantage that no amount of engineering can supply: a reader can understand instantly why an advertisement has appeared.

My own view is that the argument should be settled in favour of the reader. Targeted advertising should not be abolished, since it funds much of what is worth reading and gives small businesses access to customers they could not otherwise reach. But the collection of sensitive inferences should be prohibited outright. The targeting of children and of vulnerable groups should end. Responsibility should move from the individual to the browser, the platform and the law. The objection was never to relevance. It was to being watched.