Asked by Joe Yates

The short answer is: pure water does not conduct electricity. Any impurities, like salts, in the water enable it to conduct electricity. When salts are dissolved in water, they separate into different electrically charged atoms called ions. Salt, or sodium chloride (NaCl), breaks up into positive Na ions and negative Cl ions.
If you place a battery with a negative pole and a positive pole into water, the negative ions will be attracted to the positive pole and the positive ions will be attracted to the negative pole thus creating a closed circuit.

Amanda Mahr, Science Museum

Asked by Mark Wrangham

Like humans, fi sh need oxygen to survive, but unlike us, they are capable of getting the oxygen they need from water. To do this they use an arrangement of filaments on either side of their neck called gills. Fish gulp in oxygenated water and force it through their gills and then out through the gill openings while also continually pumping deoxygenated blood from the body into the gill fi laments. As the oxygenated water passes by the deoxygenated blood, oxygen diffuses into the gills. Efficiency is increased by the blood and water flowing in opposite directions; this is known as a counter-current exchange mechanism. Using this, a fish can extract up to 70 per cent of the oxygen dissolved in the water. Waste products in the blood can also be removed from the blood by the same process, passing from the gills into the water.

James Maclaine, Zoology department, The Natural History Museum, London

Asked by Claire Brevick

Stalactites form by deposition of various minerals held within a water solution that slowly drips vertically from the ceiling of an underground cavern or structure. As the water droplets hang, they deposit contained
minerals (often calcium carbonate). Continued downward growth in this manner is how a stalactite forms (or the reverse for stalagmites). The simplest stalactite form is a thin, hollow straw, but if excess water filters through or around the central body, then bulbous, tapered mineral cones can develop too.

HIW

Asked by Jono80

The main reason why rain clouds are dark is due to their particulate density. As clouds are formed from minuscule water droplets and/or ice crystals, the denser they are packed, the more light radiating from the Sun is scattered and dispersed by them, lending a darker appearance to their lower sections.

This is best visualised by a trip on an aeroplane, with clouds on an overcast day seeming grey/black in colour when viewed on the runway, yet a bright white when viewed from above during flight. Essentially, the deeper and denser a cloud formation is, the less light will pass through it.

HIW

Found in freshwater ponds and still bodies of waters, the water strider, or pond skater, is a predatory aquatic insect that uses the highly sensitive water-repellent hairs on its legs to detect the vibrations of an insect as it falls into the pond. The strider will then race to the location to nab its prey. Despite being denser than water, a water strider doesn’t sink; instead it exploits the principle of water tension to stay on the surface. The forces of attraction between all the molecules in the water pull the molecules at the surface together so that they lock like a thin elastic membrane of slightly denser molecules. The water strider can then cross the surface without sinking.

Water striders have three pairs of legs, the front pair of which are short and dexterous enough to clasp, kill and eat small prey. The middle pair of legs, lying fl at on the water, are used as oars to ‘row’ over the surface while the rear pair act like rudders for steering. Long, splayed legs enable the pond skater to distribute its weight evenly over a greater surface area, further helping it to float.

Asked by Ayesha Riad

Dandruff is when dead skin cells fall off the scalp. This is normal, as our skin is always being renewed. About half the population of the world suffers from an excessive amount of this shedding, which can be triggered by things like temperature or the increased activity of a microorganism that normally lives in everyone’s skin, known as malassezia globosa. Fortunately dandruff is not contagious and there are many different treatments available, like specialised shampoo.

Carlos Grau, Science Museum

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Have you had a go at our experiments? If you have, we’d love to see your efforts, so send us a photo or video to howitworks@imagine-publishing.co.uk

Lav
‘Lavatory’ comes from the Latin ‘lavatorium’, which comes from ‘layo’, which translated to modern English means ‘I wash’. Today, the word describes a washing/bathing area.

Dunny
‘Dunny’ is the Australian term for an outside toilet. The word derives from the British word ‘dunnekin’, meaning dun house. The person who empties it is called a dunnyman.

Class
The precursor to the modern flush toilet was invented by English courtier John Harington in 1596. However, it didn’t enter widespread use for another 300 years.

Duo
One of the toilet’s more recent advances has been the ‘duoset’ flushing mechanism. The first gives a smaller flush for urine, while the second gives a larger flush for faeces.

Sustain
Due to the large amounts of water used per person each day on flushing (90 litres/19.8 gallons on average), rules have been introduced to reduce the amount used by toilet systems.

Shock waves are large amplitude pressure waves produced by an object moving faster than the speed of sound like a boat or plane, or other things such as an explosion, lightning or even a moving piston.

When a source moves faster than the waves it produces, no waves will form in front of the source but will pile up behind and become compressed. The waves protruding are confined to a cone that narrows as the speed of the source increases and the waves bunch up, creating high-pressure regions outside the compressed waves. This border from inside to outside is the shock wave. The strength of a shock wave dissipates greatly with distance, much more so than a regular wave, as heat and other energy are more quickly transferred into the surrounding environment. Once enough energy has dissipated, the shock wave will become a regular wave such as a sound wave.

In this image, the USS Iowa is firing shells from its cannon that travel about twice the speed of sound. While the shells themselves will likely produce their own shock waves as they travel through the air, it is the shock wave caused by the explosion of the cannons that is visible on the water.