Karen Hill

Helium gas is not only very light, it is monatomic, its particles are all made of a single atom. As a result, helium is made up of the smallest gaseous particles possible. The atoms are only 0.1 nanometre in diameter, and are quite capable of diffusing through metal films. Because it so readily diffuses through … Read more

The seemingly well-understood candle experiment demonstrates how young and inquisitive minds are able to demolish false explanations propagated through school physics over the decades. The consumption of oxygen may well contribute to the rising water level to a certain extent, because a given mole volume of oxygen will burn the wax’s carbon into roughly the … Read more

The answer is based on some calculations which were published by the International Statistical Institute. If the world population had always been increasing at its present rate, doubling within an average human lifespan, then the living would indeed outnumber the dead. However, this is not what has happened. There have been very long periods in … Read more

Lightning usually brings the negative charge from a thunderstorm down to the ground. A negatively charged leader precedes the visible lightning, moving downwards below the clouds and through air containing pockets of positive charge. These are caused by point discharge ions released from the ground by the thunderstorm’s high electric field. The leader branches in … Read more

The sun loses about 4 million tonnes per second, which is the mass equivalent of the energy it produces through thermonuclear reactions. Another few million tonnes are lost in solar wind and other particle emissions. However, even after 2 billion years, this loss constitutes only one 10-thousandth of the sun’s mass. So the change in … Read more

Painting roofs white would reflect more sunlight and it might also compensate for global warming. The Global Rural Urban Mapping Project (GRUMP), undertaken by the Earth Institute at Columbia University in New York, shows that roughly 3 per cent of the Earth’s land surface is covered with buildings. The Earth has an albedo of 0.29, … Read more

The difference between road and rail signal color usage comes from the history of railways and the primacy of safety. The old mechanical railway signalling arms were designed so that failure, which would be in the “down” position, meant stop. The illuminated part of the signal consisted of two colored glass panels in the far … Read more

We have two types of explanation here: one physical, one chemical. It is likely that chemistry is responsible for the greater effect. The sun would be fairly low in the winter sky, its rays shining almost directly on, and perpendicular to, the vertical plane of the lenses. In the tropics, the sun could be almost … Read more

Clouds darken from a pleasant fluffy white just before rain begins to fall because they absorb more light. Clouds normally appear white when the light which strikes them is scattered by the small ice or water particles from which they are composed. However, as the size of these ice and water particles increases, as it … Read more

When the wind blows over a flat sea surface, small ripples form. These probably correspond to individual strong gusts, are disorganised and have no fixed direction or frequency. However, as the wind continues to blow, two things happen. First, the waves interact with each other to produce longer waves which means lower frequency. Secondly, the … Read more

Imagine a fly is flying in the opposite direction to a moving train. The fly hits the train head-on. As the fly strikes the front of the train, its direction of movement changes, because it hits the windscreen and continues as a blob of goo on the front of the train. At the instant it … Read more

Many old pictures and prints of wooden ships, show portholes, usually gun ports, that are square or rectangular, but ports are round in steel-hulled ships. When ships were made of wood, the architectural material was fibrous and fairly flexible, wooden ships really did creak and this was caused by timber flexure from wave action. However, … Read more

For reasons of fuel economy, large civil transport aircraft have to fly at altitudes far in excess of those capable of sustaining life. Whereas 5500 metres is about the maximum altitude at which a person can live for any extended period, a subsonic passenger jet has the best fuel economy when flying at around 12,000 … Read more

Although the aerofoil shape of an aircraft’s wing produces some of the lift in normal flight, the more important factor is the angle of attack, the angle at which the air strikes the wing. The wings of an aircraft are normally inclined to about 4° to the horizontal when compared to the main body of … Read more

The tendency of the steering wheel to return to the straight-on position is caused by the caster action of the front wheels. This effect is more clearly seen on a shopping trolley where the vertical swivel axis of each wheel is in front of the wheel-to-ground contact point. If you start pushing the trolley when … Read more

As with many things concerning the design of an aircraft, the final arrangement of various parts is based upon a series of compromises. An aircraft designer’s life would be so much easier if there were no windows at all, but so far the consensus seems to be that we should have them. Britain lost the … Read more

The disconcerting hole in the top of the parachute canopy is called an apex vent. Before the apex vent, the only way that the air trapped underneath the parachute could escape was to spill out from one edge of the canopy, thereby tilting it and throwing the hapless parachutist to one side. As the canopy … Read more

The fluorescent effect of some adhesives is well known, but there is insufficient energy in the sparks to ignite gas such as methane. The colored glow is a form of chemiluminescence. Separating the gummed surfaces requires energy that breaks the attractive forces between the molecules of gum. Presumably, the act of pulling apart the surfaces … Read more

The mirror does not reverse images from left to right, it reverses them from front to back relative to the front of the mirror. Stand facing a mirror. Point to one side. You and your mirror image are pointing in the same direction. Point to the front. Your mirror image is pointing in the opposite … Read more

Mechanical adding machines, based on rotating wheels, always have the 0 button adjacent to the 1 button. By convention, most old adding machines had the numbers increasing in value from the bottom and this may be a hangover from when the machines had levers on the wheels rather than buttons. When the numbers were put … Read more

Cling wrap, or Saran wrap, works because it acquires an electric charge as it is peeled from the roll. It can then stick to an insulating body by the same mechanism that an uncharged piece of paper sticks to the charged glass of your computer or television screen. The mechanism relies upon the cling wrap … Read more

Jello, like many materials, has both a viscous and an elastic side to its nature. It is a gel made up of a network of weak elastic bonds. These are easily broken under the shearing action caused by your fingers when using it to clean your hands. If these bonds are not broken down but … Read more

We do indeed breathe in a considerable number of molecules that once passed through Leonardo’s lungs and, unfortunately, Adolf Hitler’s or anyone else’s for that matter. The calculation is not too difficult and is as follows. The total mass of the Earth’s atmosphere is about 5 x 10^21 grams. If we take air to be … Read more

There are two answers to this question. The first is that the time for a person is the time determined by her or his circadian rhythm. Initially, this physiological time will be close to the time for the longitude where the individual lived before visiting the pole. Over a period of weeks at the pole, … Read more

When a light bulb is switched on, its delicate filament is hit with a triple whammy. The resistance of the metal filament rises with its temperature. When it is switched on, its resistance is less than a tenth of its usual working level so an initial current more than 10 times the rated value surges … Read more

The sounds from plastic bags are generated mostly by you, because the bag will not rustle by itself. The noise is caused by sharp movements of the kind you get when a stiff plate buckles or gets rubbed. The bags are made of polyethylene film which, untreated, is waxy and floppy and not very noisy. … Read more

In considering the origin of tides we must disregard the Earth’s daily rotation around its axis and concentrate only on the revolution of the Earth-Moon system. This revolution takes place around the system’s common centre of gravity, which is about halfway from the surface to the centre of the Earth, and causes every point in … Read more

The claim of the Great Wall of China being visible from space is incorrect. It is well known as one of the most widely believed urban legends, perhaps second only to the famous one about mass suicide by lemmings. A person with perfect eyesight is able to resolve up to about one minute of arc … Read more

The sky is blue on a clear day because of a process called Rayleigh scattering. Light arriving from the sun hits the molecules in the air and is scattered in all directions. The amount of scattering depends dramatically on the frequency, that is, the color of the light. Blue light, which has a high frequency, … Read more

Midday refers to the moment when the sun crosses the local meridian, which is one of the imaginary lines joining the North and South Poles at 90° to the equator. If you set your watch so that noon occurs as the sun crosses the meridian, the day will be of equal length either side of … Read more

Clearly a spacecraft or probe will not make any net gain in energy by simply falling through a stationary gravity field. However, Jupiter and its gravity field are moving around the sun at a speed of about 1300 metres per second and any probe passing behind the planet will be accelerated by this moving gravity … Read more

The sea is salty because the rivers that flow into it wash salts and other minerals out of the ground. The salts dissolve in the rivers and the rivers flow into the sea. As the sun evaporates the water from the sea to make clouds, it leaves the salts and minerals behind, so the sea … Read more

If you leave the lid off your electric kettle and switch on, you can see what is happening. The heating element quickly becomes covered with small silvery bubbles, each about 1 millimeter in diameter. These are air bubbles, forced out of solution by heat from the element. Rough parts of the element’s metal surface provide … Read more

Why Is Scotch Tape Transparent When Pulled From a Roll Quickly But When Scotch Tape Is Pulled Slowly It’s Opaque? The reason for the difference in behavior lies in the response of the adhesive layer on the tape to the rate at which it is stressed. When the tape is peeled back slowly, the adhesive … Read more

The nasty smell of a trashcan is most likely caused by bacteria and fungi feeding on the organic matter in the trash. It will be most noticeable if the bin is in a warm and damp place. Bacteria love it when it’s warm and damp and multiple quickly. The smell will not always be exactly … Read more

Super Glue will not stick to the inside of its tube because the tube contains oxygen in the form of air but excludes water. Oxygen inhibits whereas water catalyzes. Super Glue doesn’t stick to the inside of the tube because, being based on a cyano-acrylate monomer, it requires moisture in the form of water or … Read more

The corkscrew effect you may notice is the bottom end of the whirlpool that is occurring inside the container as the milk exits. The force that causes liquid to corkscrew or spiral is usually called the Coriolis force, or Coriolis effect. This is responsible for all whirlpooly stuff you might find. Milk cartons and bottles … Read more

The reason that freshly boiled water is more effective for making tea or coffee than water boiled twice is that the fresh water has a higher oxygen content. This should result in a tastier cup of tea because more tea will be extracted from the tea leaves. This can be easily demonstrated by placing a … Read more

The honeycomb cells observed in heated cooking oil are known as Rayleigh-Benard convection cells. At low temperature differences between the bottom and the top of the oil, the heat is dissipated through ordinary thermal transport, or collision of individual molecules, and no macroscopic motion can be observed. At greater temperature differences, convection, a collective phenomenon … Read more

Eggs with two yolks are a natural phenomenon over which we have no control. Double yolk eggs are larger than those laid by the majority of the flock and are set aside to be tested individually. Demand for double yolkers far outstrips supply and we need to be very sure that they do in fact … Read more

When a carton of liquid is tipped during pouring, the free surface of the liquid in the container is raised relative to the opening. This creates a pressure difference between the free surface and the opening, which forces fluid from the carton. In addition to this pressure force, there are also surface tension forces acting … Read more

Uncooked cheese contains long-chain protein molecules more or less curled up in a fatty, watery mess. When you heat cheese, the fats and proteins melt and if you fiddle with the fluid, the chains can get dragged into strings. Grab a bit of the molten cheese and pull, and you get a filament, in much … Read more

Cookies or biscuits contain much more sugar and salt than bread like baguettes, which is the main reason why they become soft if left out. The finely divided sugar and salt are hygroscopic and soak up moisture from the atmosphere, the osmotic pressure in a sweet biscuit is quite high. The dense texture of a … Read more

The force that moves cereal to the sides of the bowl is due to an imbalance in the pull from the surface tension of the liquid around the sides of the floating piece of cereal. A simple experiment explains what is happening. You need tap water and two polystyrene cups plus two small pieces taken … Read more

A greenish iridescent sheen is often found on foods containing traces of fat in water. When it is cool this mix separates out microscopically into a film, like oil on a wet road. In some types of cold meats, such as sliced silverside of beef or some hams, you may see a handsome opalescence. The … Read more

When you boil water in the microwave, a portion of the water in the cup is becoming superheated. This means the liquid temperature is actually slightly above the boiling point, where it would normally form a gas. In this case, the boiling is hindered by a lack of nucleation sites needed to form the bubbles. … Read more

The infamous black mold is the fungus Aspergillus niger. The reason it seems so difficult to eradicate is that the visible black manifestation is merely the exposed structure of the fungus, which is mainly comprised of the fruiting bodies. In addition to this visible material, there is invariably an insidious network of hyphae or mycelia … Read more

Many keen home brewers feel qualified to answer the question on the ageing of lagers. All true lagers are aged before consumption. The word Lager, in fact, comes from the German word meaning “to store”. After fermentation, the beer undergoes a storage, or lagering, process at low temperature to allow the beer to mature and … Read more

What we normally refer to as “taste” is more correctly termed flavor, which is made up of taste, irritation and aroma. Taste per se consists only of the five sensations that can be detected by the tongue: salt, sweet, sour, bitter and umami. These are not affected by temperature and nor is irritation from, for … Read more

Not all changes between solid and liquid are to do with melting or cooling, including congealing scrambled eggs and polymerisation of plastics. Yolk and albumen, egg white, get their textures from globular proteins dissolved in them. The globules form because the chain-like protein molecules curl up into balls. Electric charges at particular positions on the … Read more

Counter-intuitive though it may be, it does appear that hot water can freeze more quickly in a refrigerator. Better thermal contact if the water container is placed into an iced-up freezer compartment and a different pattern of convection currents which allow hot water to freeze faster seem the best explanations. Which effect predominates depends on … Read more

A falling drop of rain creates a tiny pressure wave ahead, below the raindrop. This wave pushes the fly, gnat, wasp, bee, or insect sideways and the drop misses it. Fly swatters are made from mesh or have holes on their surface to reduce this pressure wave, otherwise flies would escape most swats. The insect … Read more

Conkers, or conker fighting appears to be a mainly British pursuit so we realise we have to enlighten the rest of the world. Conkers are the hard fruit of the horse chestnut tree. These are collected in autumn, removed from their spiky casing and left to mature. A hole is then drilled in the conker, … Read more

The simplest and best way to harden conkers is to put them away in a drawer until the following year. However, if they were not attached to a string when new and soft they will have to be drilled. Many children and grandchildren have played with leftover conkers, some of which were 50 years old. … Read more

The infamous case of the flightless bumblebee is a classic example of being careless with approximations. It stems from someone trying to apply a basic equation from aeronautics to the flight of the bee. The equation relates the thrust required for an object to fly to its mass and the surface area of its wings. … Read more

Red meat is red because the muscle fibers which make up the bulk of the meat contain a high content of myoglobin and mitochondria, which are colored red. Myoglobin, a protein similar to haemoglobin in red blood cells, acts as a store for oxygen within the muscle fibers. Mitochondria are organelles within cells which use … Read more

It is a common misconception that the white droppings produced by birds are feces. In fact, they are urine. Birds excrete uric acid rather than urea because it is an insoluble solid. This way they avoid wasting water when urinating, just one of their adaptations for a good power-to-weight ratio. The white material that comprises … Read more

Eggs are egg-shaped, or ovoid for several reasons. First, it enables them to fit more snugly together in the nest, with smaller air spaces between them. This reduces heat loss and allows best use of the nest space. Second, if the egg rolls, it will roll in a circular path around the pointed end. This … Read more

Anisette-based drinks rely on aromatic compounds called terpenes for their flavor. These terpenes are soluble alcohol, but not in water. The 40 per cent or so alcohol in the drink is enough to keep the terpenes dissolved, but when the drink is mixed with water they are forced out of solution to give a milky-looking … Read more

We wouldn’t recommend putting bananas in the fridge to keep them fresh. Like all living organisms bananas adjust the composition of their cell membranes to give the right degree of membrane fluidity for the temperature at which they normally live. They do this by varying the amount of unsaturated fatty acids in the membrane lipids: … Read more

While a majority of dogs have black noses, not all do. The noses of dogs such as vizslas and weimaraners match their coat colors, red and silver, respectively, and it is not unusual for puppies of any breed to start out with pink noses that then darken as the animal matures. Some Shetland sheepdogs retain … Read more

Polar bears would probably survive in the Antarctic, and the Southern Ocean around it, but they could devastate the native wildlife. In the Arctic polar bears feed mainly on seals, especially young pups born on ice floes or beaches. Many of the differences in breeding habits between Arctic and Antarctic seals can be interpreted as … Read more

Onions and garlic both contain derivatives of sulphur-containing amino acids. When an onion is sliced, one of these compounds, S-propenyl-L-cysteine sulfoxide, is decomposed by an enzyme to form the volatile propanthial S-oxide, which is the irritant. Upon contact with water, in this case your eyes, the irritant hydrolyses to propanol, sulphuric acid and hydrogen sulphide. … Read more

Beer, sparkling wine, a Coke, and other fizzy drinks are liquids which are supersaturated with gas. Although thermodynamics favours the gas bubbling out of the dissolved state, bubble formation is unlikely since bubbles must start small. The pressure of these tiny bubbles can reach about 30 atmospheres in a bubble only 0.1 micrometres in diameter. … Read more

Ice made in domestic freezers is inevitably cloudy because of the dissolved air that tap water contains, around 0.003 per cent by weight. As the water in the ice trays drops below freezing point, crystals form around the edges of the compartments. These are pure ice and they contain very little air because the solubility … Read more

Wine is left to breathe to allow the volatile and aroma-bearing substances to start evaporating, so that we may enjoy the bouquet. Shaking a drink is completely different. An agitated drink incorporates gas, letting oxygen reach as much liquid as possible. This oxidised liquid provides a very different taste. For some drinks this taste may … Read more

Of all the body cavities in contact with the outside world, the nose is probably one of the most hospitable. The nose is warm, very well aerated, moist and supplies unlimited quantities of bacterial food secreted continuously by the nasal mucosa, mucus contains quantities of glycoprotein and dissolved salts. In other words it is an … Read more

Plenty of studies have looked at pain associated with the weather, especially in people suffering from arthritis. These show that there is a real effect, but oddly there has been little research into what causes the pain. The human body can be viewed schematically as a clump of gelatin-filled balloons mounted on a stick. Undamaged … Read more

Placebos are substances with no pharmacological properties, such as sugar or dummy pills. The word placebo means “I shall please” in Latin, and was first used in a medical context in the 18th century. They are widely used as a control in experiments to test the effect of medicines, and are made to look and … Read more

The annoying runny nose that occurs while we’re awake is caused by your head position. When we sleep, almost all the post-nasal drip drains down the throat because we are lying down, sometimes on our sides and sometimes on our backs. Many of us suffer from this problem and, like a massage table that had … Read more

You get a dry mouth during public speaking because when you are nervous the body is set into the fight or flight state. This is caused by an activation of the autonomic nervous system. It is seen throughout the animal kingdom, and has evolved to help the animal deal with dangerous situations, when escaping from … Read more

When a bolt of electricity, such as a lightning bolt, hits a watery surface, the electricity can run to earth in a myriad of directions. Because of this, electricity is conducted away over a hemispheroid shape which rapidly diffuses any frying power possessed by the original bolt. Obviously, if a fish was directly hit by … Read more

Sheep and other animals run ahead of cars because they do not realise that cars cannot climb grassy banks. Ancestral sheep were pursued by wolves and big cats. If an animal tries to turn aside some yards from the hunter, the pursuing animal sees what is happening, makes an easy change of course and intercepts … Read more

Fish jumping out of tanks small or large is quite a common problem for enthusiasts, and is the reason why some owners choose to have a glass cover on the top of their aquarium. There are several theories as to why fish might jump from a small aquarium. It has been suggested that one reason … Read more

Birds have a nifty tendon arrangement in their legs which help them sleep when they are perched. The flexor tendon from the muscle in the thigh reaches down over the knee, continues down the leg, round the ankle and then under the toes. This arrangement means that, at rest, the bird’s body weight causes the … Read more

Most of us assume fish don’t fart because we don’t see a string of bubbles coming out from a fish’s bum. However, fish, yes, even your pet Goldfish or Guppy, do develop gas in the gut, and this is expelled through the vent, just like any other animal. The difference is in the packaging of … Read more

The usual explanation for flight in flying fish is as a way to escape predation, particularly from fast-swimming dolphin-fish. Flying fish do not fly to catch insects, flying fish are largely oceanic and flying insects are rare over the open sea. It has been suggested that their flights, which are actually glides, because flying fish … Read more

Penguins, like other birds that live in a cold climate, have adaptations to avoid losing too much heat in the winter and to preserve a central body temperature of about 40 °C. The feet pose particular problems since they cannot be covered with insulation in the form of feathers or blubber, yet have a big … Read more

The answer is quite simple. In a conventional microwave, the waves are spaced a certain distance apart, because that is all that is needed to cook the food properly. The ants are so minute that they can dodge the rays and so survive the ordeal. The phenomenon that the ants take advantage of is that … Read more

Toadstools that force their way up through asphalt are probably ink-cap mushrooms (Coprinus) growing on buried plant debris. They are pushing upwards because their stalks function as vertical hydraulic jacks. The upward pressure comes from the turgor pressure of the individual cells making up the wall of the hollow stalk of the mushroom. Each individual … Read more

The reason that people start to walk like each other and synchronize their steps is that they have a subconscious need to show their companion that they agree with them and so fit in with them. This is also a signal to other people that “we are together, we are synchronized”. Other studies suggest that … Read more

When approaching obstacles, right-handed people will, in most cases, avoid them by going to the right, while left-handed people will go to the left. If two same-handed people approach an obstacle from the opposite direction they will walk safely around it without bumping into one another en route. If two people of different handedness approach … Read more

If someone was tickling you and you were able to remain relaxed, it would probably not affect you at all. Of course, it is often difficult to stay relaxed when being tickled, because tickling causes tension for most of us, such as feelings of unease due to physical contact, the lack of control and the … Read more

It doesn’t just happen in movies. When you are thrown horizontally across a room after touching a live electrical connection, the force comes from your own muscles. When a large electrical current runs through your body, your muscles are stimulated to contract powerfully, often much harder than they can be made to contract voluntarily. Normally … Read more

When you need to concentrate on something, like a crossword puzzle, you are using the hemisphere of the brain also used for processing motor input. It is pretty funny to see people slow down when they are thinking of something difficult while walking. This is caused by interference from the two activities fighting for the … Read more

The surface of the brain has fissures or folds to increase the surface area for the cortex. Dumber animals such as rats have smooth brains. Much of the work carried out in the brain is performed by the top few layers of cells, a lot of the brain’s volume is, in effect, point-to-point wiring. So, … Read more

Sound travels faster in helium than in air because helium atoms, with atomic mass 4, are lighter than nitrogen and oxygen molecules, which are molecular mass 14 and 16 respectively. In the human voice, as in all wind instruments, the sound is produced as a standing wave in a column of gas, normally air. A … Read more

Dandruff is believed to be caused by overgrowth of yeasts such as Pityrosporum ovale which live on normal healthy human skin. Also known as pityriasis simplex capillitii, dandruff is sometimes caused by frequent exposure to extreme heat and cold. The scalp specific fungus, Malassezia globosa, causes local irritation resulting in hyperproliferation of the cells, or … Read more

Non-decay of a dead body is more common than most people think. Many saints have had their claim to sainthood upheld by the nifty trick of not going off after burial. More mortal examples include the wife of Dante Gabriel Rossetti, who troubled him somewhat by being revealed in all her undecayed glory when, short … Read more