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On the flipside
In a recent ‘Q& A’ (Summer, p86) you answered a question by Coco Shang that indicates that work was still going on into the reason for toast to usually land butterside down on being dropped.
This is an old chestnut, and surely any school boy will tell you that the usual reason for this occurrence is that the toast was probably buttered on the wrong side in the first place. Peter Duckworth, Ceredigion
Re: the ‘Q& A’ question about toast, I recommend ALL scientists to read the excellent book Eurekas And
Euphorias by Walter Gratzer. On page 45, he describes a US scientist investigating this very problem, who found his children’s toast always fell butter-side up. He only discovered later that his children buttered BOTH sides of their toast! Stuart Ching, via email
Trying tyres
Helen Czerski presents us with an interesting puzzle in her latest column (Summer, p76). May I suggest the following explanation? From her description, the nail seems to have entered through the thicker, treaded part of the tyre, and then pierced the thinner sidewall, next to the rim. When first entering the tyre, the nail would drag after it a cone of stretched rubber from the inner tube, as Helen suggests – a skirt around the nail. On exiting the other side, the nail would not be able to deform the
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inner tube to the same extent, as it would be supported by the outer casing. Also the nail would not travel as far through the exit hole as it had through the entry hole.
Once the head of the nail was flush with the tyre tread and the wheel rolled forward, the nail would be drawn back out very slightly due to the skirt at the entry point being greater, and therefore stronger, than that at the exit point. This would result in a small internal rubber skirt at the exit point but there would still be enough of the internal skirt at the entry point to maintain the seal.
During the remainder of the journey, every time the nail head hit the ground it would be pressed in flush again but would immediately pop back out. The movement would be very small, especially with high pressure in the tyre, and deformation at the point of road contact would be minimal. It appears this very slight movement was not enough to cause the seals to fail although, as Helen says, you have to wonder how much farther (not further!) it would have held up.