Thread for heights: Some species of spiders are known for 鈥渂allooning鈥�. On a hot day they climb to the top of a tall object and run out a thread, gripping with their legs until the thread is long enough to provide them with sufficient lift. Then they release their grip and fly. The lift has been attributed to crosswinds, but this seems unlikely, as there is no aerofoil involved and ballooning has been observed in still air.
It may be that the lift is provided by convective air dragging along the length of the thread. But how does such an insubstantial thread generate enough lift? If it did, wouldn鈥檛 this cause problems with webs, or is there a different kind of thread used for ballooning?
The Blob: About ten years ago, I stored a solution of ferric chloride used to etch copper laminate printed circuits in a clear, flat-bottomed milk bottle. A dull copper-coloured sludge settled out which I was surprised to see was an almost perfect hemisphere (not a bubble) of about 3.5 centimetres radius. Why?
Advertisement
Drip dry: If I alight from the bus and it is raining, I tend to run for my door, in the belief that I will arrive home less wet than if I walk. However I have heard that the same number of raindrops will strike me whether I run or walk. Is this really the case?