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Sitting pretty
The back pages Almost the last word Is sitting inherently bad for you or just time that could be better spent exercising?
Lightning bulb
Storm Dunlop East Wittering, West Sussex, UK The sizzling sound was almost certainly a corona discharge and is often heard before a nearby lightning flash. The discharge occurs when the electrical field between the cloud and the ground is strong enough to cause electrons to be emitted from the tips of any pointed objects – even, in some cases, from people’s hair. As for why the light glowed, it depends on the type of lamp. If it is one that glows after being charged during the day, the flash may have provided sufficient charge for the light to come on. If it is activated by passive infrared (PIR) radiation, it is possible that the heat from the lightning was sufficient to activate the PIR sensor. John Woodgate Rayleigh, Essex, UK Both effects are due to the electric field that is generated between the thundercloud and the ground. The light is caused by a current that is induced in the wiring of the lamp by the varying electric field through its accompanying magnetic field. These fields persist for a while at a lower level than the very strong fields created just before and during a strike. Anthony Richardson Ironbridge, Shropshire, UK It is unclear whether the bulb was powered by the intense light absorbed from the lightning by the solar panel or, in a less likely scenario, by charge absorbed from the air. The sizzling sound must be the sound of the air being explosively expanded in the lightning channel. 54 | New Scientist | 21 September 2019
GETTY IMAGES
A summer storm woke me around 2 am. I heard a sizzling sound before lightning struck about 100 metres away. Then I saw a 1.5-volt solarpowered outside light glowing like a 50-watt bulb. It faded after a few minutes. What caused the sizzling sound and made the light glow so brightly?
This week’s new questions Sitting pretty We are frequently told we need plenty of exercise and that sitting is bad for us. Is the problem with sitting merely that it stops you exercising, or is sitting bad in itself? John Gordon, Datchworth Green, Hertfordshire, UK Coil conversion If I compress a metal spring, tie it with an acid-proof binding then submerge it in acid and dissolve the spring, what happens to the energy that was used to compress it? I think the acid must warm up, but how is the stored energy converted to heat? Roger Key, Bedale, North Yorkshire, UK
Hard-baked Why do crisp ginger biscuits go soft if left exposed to the air for a couple of days when other baked products, such as cakes and bread, go hard?
Krista Nelson Rokeby, Tasmania, Australia The difference between a cake and a biscuit is similar to the difference between bread and toast. Bread starts out soft and moist but dries out over time and becomes an unpleasant mix of soft and dry. Toast is made by drying out bread to make it crisp. As toast ages, it absorbs moisture, making it rubbery and unpleasant. Biscuits are the toast of the cake world and were originally made by baking cakes twice to dry them out for storage. If you leave a cake and a biscuit in a standard kitchen, the moist cake will dry out and the dry biscuit will become soggy, both approaching the same state, just from different directions.
Claire Gregson Portadown, County Armagh, UK Biscuits are essentially dried cakes, so absorb ambient moisture. Cakes are much more moist, so evaporate water to the surrounding air. Just eat and enjoy. David Jackson Liverpool, UK Biscuits start out with a very low moisture content of between 1 and 3 per cent, depending on the type, whereas this is around 15 to 30 per cent for cakes. In an atmosphere of moderate humidity, water will diffuse out of a cake and into a biscuit until equilibrium is reached, not only with the entrapped air, but also the starchy, sugary matrix of the product. In the 1990s, biscuit and cake manufacturer McVitie’s fought a
UK tax claim on its Jaffa Cakes. Chocolate-coated biscuits are subject to value-added tax (VAT) in the UK, whereas chocolatecoated cakes aren’t, so a huge amount of money was at stake. McVitie’s (my employer at the time) won the case, partly because cakes, including Jaffa cakes, become dry when they go stale, whereas biscuits go soft. Gerald Dorey Oxford, UK This question is an example of the profound cake-biscuit existential problem exemplified by the Jaffa Cake. This chocolatecoated confection has provoked much discussion: a BBC radio programme that discussed the subject even invoked Ludwig Wittgenstein’s ideas of the futility of “family resemblance” tests, whether a categorisation is merely a semantic reflex and whether a non-binary category might be applied. Lawyers are more practically minded, and in 1991, a UK VAT tribunal decided that the critical factor was whether the item absorbs moisture over time and becomes softer, as with biscuits, or gives up moisture and hardens, as with cake. This confirmed that the Jaffa Cake is a cake, and is therefore liable for a lower rate of tax than it would have been if classified as a biscuit. Clearly, the ambient humidity is critical. I would suggest that in countries with weather that is hot and humid enough to melt the chocolate on a Jaffa Cake, no cake would harden, nor would a biscuit stay hard for long. The reverse would be true in deserts. In both areas, the cake-biscuit duality disappears. ❚
Want to send us a question or answer?
Email us at [email protected] Questions should be about everyday science phenomena Full terms and conditions at newscientist.com/lw-terms
Lightning bulb
Storm Dunlop East Wittering, West Sussex, UK The sizzling sound was almost certainly a corona discharge and is often heard before a nearby lightning flash. The discharge occurs when the electrical field between the cloud and the ground is strong enough to cause electrons to be emitted from the tips of any pointed objects – even, in some cases, from people’s hair. As for why the light glowed, it depends on the type of lamp. If it is one that glows after being charged during the day, the flash may have provided sufficient charge for the light to come on. If it is activated by passive infrared (PIR) radiation, it is possible that the heat from the lightning was sufficient to activate the PIR sensor. John Woodgate Rayleigh, Essex, UK Both effects are due to the electric field that is generated between the thundercloud and the ground. The light is caused by a current that is induced in the wiring of the lamp by the varying electric field through its accompanying magnetic field. These fields persist for a while at a lower level than the very strong fields created just before and during a strike. Anthony Richardson Ironbridge, Shropshire, UK It is unclear whether the bulb was powered by the intense light absorbed from the lightning by the solar panel or, in a less likely scenario, by charge absorbed from the air. The sizzling sound must be the sound of the air being explosively expanded in the lightning channel. 54 | New Scientist | 21 September 2019
GETTY IMAGES
A summer storm woke me around 2 am. I heard a sizzling sound before lightning struck about 100 metres away. Then I saw a 1.5-volt solarpowered outside light glowing like a 50-watt bulb. It faded after a few minutes. What caused the sizzling sound and made the light glow so brightly?
This week’s new questions Sitting pretty We are frequently told we need plenty of exercise and that sitting is bad for us. Is the problem with sitting merely that it stops you exercising, or is sitting bad in itself? John Gordon, Datchworth Green, Hertfordshire, UK Coil conversion If I compress a metal spring, tie it with an acid-proof binding then submerge it in acid and dissolve the spring, what happens to the energy that was used to compress it? I think the acid must warm up, but how is the stored energy converted to heat? Roger Key, Bedale, North Yorkshire, UK
Hard-baked Why do crisp ginger biscuits go soft if left exposed to the air for a couple of days when other baked products, such as cakes and bread, go hard?
Krista Nelson Rokeby, Tasmania, Australia The difference between a cake and a biscuit is similar to the difference between bread and toast. Bread starts out soft and moist but dries out over time and becomes an unpleasant mix of soft and dry. Toast is made by drying out bread to make it crisp. As toast ages, it absorbs moisture, making it rubbery and unpleasant. Biscuits are the toast of the cake world and were originally made by baking cakes twice to dry them out for storage. If you leave a cake and a biscuit in a standard kitchen, the moist cake will dry out and the dry biscuit will become soggy, both approaching the same state, just from different directions.
Claire Gregson Portadown, County Armagh, UK Biscuits are essentially dried cakes, so absorb ambient moisture. Cakes are much more moist, so evaporate water to the surrounding air. Just eat and enjoy. David Jackson Liverpool, UK Biscuits start out with a very low moisture content of between 1 and 3 per cent, depending on the type, whereas this is around 15 to 30 per cent for cakes. In an atmosphere of moderate humidity, water will diffuse out of a cake and into a biscuit until equilibrium is reached, not only with the entrapped air, but also the starchy, sugary matrix of the product. In the 1990s, biscuit and cake manufacturer McVitie’s fought a
UK tax claim on its Jaffa Cakes. Chocolate-coated biscuits are subject to value-added tax (VAT) in the UK, whereas chocolatecoated cakes aren’t, so a huge amount of money was at stake. McVitie’s (my employer at the time) won the case, partly because cakes, including Jaffa cakes, become dry when they go stale, whereas biscuits go soft. Gerald Dorey Oxford, UK This question is an example of the profound cake-biscuit existential problem exemplified by the Jaffa Cake. This chocolatecoated confection has provoked much discussion: a BBC radio programme that discussed the subject even invoked Ludwig Wittgenstein’s ideas of the futility of “family resemblance” tests, whether a categorisation is merely a semantic reflex and whether a non-binary category might be applied. Lawyers are more practically minded, and in 1991, a UK VAT tribunal decided that the critical factor was whether the item absorbs moisture over time and becomes softer, as with biscuits, or gives up moisture and hardens, as with cake. This confirmed that the Jaffa Cake is a cake, and is therefore liable for a lower rate of tax than it would have been if classified as a biscuit. Clearly, the ambient humidity is critical. I would suggest that in countries with weather that is hot and humid enough to melt the chocolate on a Jaffa Cake, no cake would harden, nor would a biscuit stay hard for long. The reverse would be true in deserts. In both areas, the cake-biscuit duality disappears. ❚
Want to send us a question or answer?
Email us at [email protected] Questions should be about everyday science phenomena Full terms and conditions at newscientist.com/lw-terms