Category Archives: Science

Health, Medical, Science

Questions of Science: ‘Rubbing salt in to the wound’…

Health

Rubbing salt in the wound was a way of preventing infection. But how did it work?

Applying salt to a wound creates a highly saline environment, one in which it is difficult for microbes to grow. The high concentration gradient between the salt solution and the fluid inside bacterial cells makes it far more difficult for the microbes to extract water from the solution without using a lot more energy. As a result, the bacteria become placid and dehydrated and cannot function normally or proliferate.

Concentrated sugar solutions also have a dehydrating effect. This accounts for the extended shelf life of chutneys and preserves, and explains why honey can be used on wound dressings and, ironically, on bee stings as an antiseptic.

Blood is 83 per cent water. Because salt is hygroscopic, it absorbs water, accelerating the tendency for blood to clot and drying the wound. This helps deny microorganisms a favourable habitat. Saline solutions do generate osmotic pressure – it forces water out of microbes to equalise the salt concentration across their cell membranes. This can kill them, so salt acts as a disinfectant.

The stinging of the wound signals that salt does cause injury to the body. But in the absence of a better option at the time, killing a few healthy skin cells was deemed acceptable collateral damage when the alternative may have been a serious infection or possible death.

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Arts, History, Science, Society

Quantum Leaps: Archimedes…

c. 287 – 212 BC

“Give me a place to stand on, and I will move the earth,” Archimedes is reputed to have declared to the people of Syracuse. The practicalities of an earth-bound life may have denied him that particular pedestal but arranging for his patron King Heiron to move a ship by pushing a small lever was considered only a slightly miraculous feat. With such audacious displays, along with his brilliance as an inventor, mechanical scientist and mathematician, it is no wonder Archimedes was so popular and highly regarded among his contemporaries.

The Mathematician

It was not only his peers, however, who benefited from Archimedes’ work. Many of his achievements are still with us today. First and foremost, Archimedes was an outstanding pure mathematician, “usually considered to be one of the greatest mathematicians of all time,’ according to the Oxford Dictionary of Scientists. He was, for example, the first to deduce that the volume of a sphere was 4πr³ x 3, where r is the radius. Other work in the same area, as outlined in his treatise On the Sphere and Cylinder, led him to deduce that a sphere’s surface area can be worked out by multiplying that of its greatest circle by four: or, similarly, a sphere’s volume is two-thirds that of its circumscribing cylinder. He calculated pi to be approximately 22/7, a figure that was widely used for the next 1500 years.

The Archimedes Principle

Archimedes also discovered the principle that an object immersed in a liquid is buoyed or thrust upwards by a force equal to the weight of the fluid it displaces. The volume of the displaced liquid is the same as the volume of the immersed object. Legend has it that he discovered this when set a challenge by King Heiron to find out whether one of his crowns was made of pure gold or was a fake. While contemplating the problem Archimedes took a bath and noticed that the more he immersed his body in the water, the more the water overflowed from the tub. He realised that if he immersed the crown in a container of water and measured the water that overflowed he would know the volume of the crown. By obtaining a volume of pure gold equivalent to the volume of water displaced by the crown and then weighing both the crown and the gold, he could answer the King’s question. On making this realisation, Archimedes is said to have leapt from his tub and run naked along the street shouting ‘Eureka!’, ‘I have found it!’

Levers and Pulleys

Indeed, it was the practical consequences of Archimedes’ work which mattered more to his contemporaries and for which he became famous.

One such practical demonstration allowed King Heiron to move a ship with a single small lever – which in turn was connected to a series of other levers. Mathematically, he understood the relationship between the lever length, fulcrum position, the weight to be lifted and the force required to move the weight. This meant he could successfully predict outcomes for any number of levers and objects to be lifted.

Likewise he came to understand and explain the principles behind the compound pulley, windless, wedge and screw, as well as finding ways to determine the centre of gravity in objects.

Archimedes goes to war

Perhaps the most important inventions to his peers, however, were the devices created during the Roman siege of Syracuse in the second Punic War. The Romans eventually seized Syracuse, due to neglect of the defences, and Archimedes was killed by a Roman soldier while hard at work on mathematical diagrams. His last words are reputed to have been, ‘Fellow, do not disturb my circles!’

Further achievements

Inventions

. Archimedes’ Screw: a device used to pump water out of ships, and also to irrigate fields.

. Archimedes’ Claw: a huge war machine designed to sink ships by grasping the prow and tipping them over, used in the defence of Syracuse.

. Compound pulley systems: enabled the lifting of enormous weights at a minimal expenditure of energy.

. The method of exhaustion: an integral-like limiting process used to compute the area and volume of two dimensional lamina and three-dimensional solids.

Discoveries

. Archimedes was responsible for the science of hydrostatics, the study of the displacement of bodies in water. He also discovered the principles of static mechanics and pycnometry (the measurement of the volume or density of an object).

. Known as the ‘father of integral calculus’, Archimedes’ reckonings were later used by, among others, Kepler, Fermat, Leibniz and Newton.

. Science Book

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Science, Society, Technology

Questions of Science: The Large Hadron Collider…

Why does the Large Hadron Collider (LHC) have to be so physically large, when it is only designed to detect particles that are extremely tiny?

The LHC is a synchrotron, a circular accelerator that uses carefully synchronised electromagnetic fields to accelerate particles to very high speeds. When this involves charged particles on a curved path they release synchrotron radiation, which wastes energy. This is not desirable because most of the particles that physicists are looking for, such as the recently discovered Higgs boson, have large masses and can only be created in high-energy collisions.

The large radius of the LHC’s track is big enough to limit the radial acceleration given to the particles, thus minimising the loss of energy the particles suffer as synchrotron radiation. The superconducting magnets used to control the flow and direction of the particles can accelerate them up to speeds in excess of 99.99 (but less than 100) per cent of the speed of light.

The magnets lie central in answering the question. The size of the LHC is actually a trade-off between three things: the magnets that are available; the energy (or velocity) it is necessary to give the particles; and, the feasible dimensions of the structure.

The faster the particles are moving, the more likely you are to see something interesting happen in a collision. So, it’s important to accelerate the particles, mainly protons, as much as possible.

The protons need to follow a circular path so they can be continuously accelerated by an electric field, and this is done using magnets positioned around the tunnel. The faster the protons travel, the stronger the magnetic fields need to be to keep them on track.

To increase energy there are two possible choices: make the magnets stronger or the accelerator ring larger, so that the particles’ path does not need to be bent so much. At some point there is either a technological or financial limit on the strength of the magnets, leaving the ring size as the only remaining variable.

However, to keep the costs of the project manageable, the LHC was built in an existing tunnel that housed a previous experiment, called the Large Electron-Positron Collider. So the energy to which protons can be accelerated was actually predetermined by limits of technology and funding.

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