Science: Technoquest

Q When you see pictures of launches of the Saturn V rockets, you see lots of smoke. Why?

The Apollo Saturn V rocket sits on top of a large hole. The engine nozzles dangle into a large free space (enough for a five-storey block of flats) which is used to dissipate the exhaust gases. If the nozzles were pointing at a solid surface the heat would melt it and the gas rebounding from the surface would destroy the rocket.

Near the bottom of the hole are some exits known as flame trenches. They let the gases escape back up to ground level so that they don't hit the rocket, or the launch tower and control equipment.

Imagine the Saturn V on top of its "hole" just before launch. A few seconds before the engines start, large water jets are started. They pour water down the hole. They flood the air with water droplets and cool the air as well as dragging it down the hole, setting up a massive downwards wind. When the engines ignite, the wind makes the exhaust go down the hole towards the flame trenches. The engine nozzles are surrounded by a cold down-draught that simulates what they will experience in the atmosphere. It takes a few seconds for the engines to reach full power, the burning to stabilise and the nozzles to reach the right temperature. The exhaust gases start to emerge from the end of the flame trench and the rocket appears to be surrounded by smoke.

Q How do sweet-makers get the letters to go all the way through seaside rock?

Rock is made from sugars. First the sugars are heated up to about 300C to make a syrup, some of which is coloured. The rest is put through a pulling machine in which lots of tiny air bubbles are included, giving it a white colour. The rock at this stage is still hot and as it cools down it becomes like Plasticene and can be easily moulded.

While still warm the rock is rolled into long, thin tubes. The letters are then made by placing coloured tubes in among white ones to make a large (say, 5cm across) version of a stick of rock.

This large stick of rock is put on to a "batch roll", which keeps the rock in its cylindrical shape, and it is then extruded by hand, becoming thinner and thinner until it is the size and shape that is wanted.

This process has to be done when the rock is still soft, so it has to be done quickly. The maximum number of letters that can be put in a rock depends upon the speed and expertise of the rock-maker. If the rock becomes completely cool, and therefore hard, before the above procedure is finished, the whole lot has to be thrown away.

Q What type of corpse are the scatopsid (filthy fly larva) found on?

Scatopsidae is a rather poorly known family of flies (Diptera), at least in terms of their biology. As far as it is known, most species breed in a variety of decaying plant and animal materials, eg rotting wood, damp compost, excrement and decomposing fungi. They are not typically associated with corpses, although some can breed in a wide variety of decaying substances and therefore could possibly do so in carrion at times, but as far as I know this has not yet been observed. Adult scatopsids are most often seen on flowers, and large numbers may sometimes be seen on vegetation following mass emergence near a breeding-site.

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