User Reviews

I thought this was a pretty good episode. I have to hold up to questioning the reviewer who claims "Bad science". They may be right, but let us investigate. They claim that a bullet falling back, having been fired from the ground, is not capable of causing serious injury. Well, there we immediately have a serious issue. We have evidence (anecdotal, but supported by Valerius Maximus and Pliny the Elder) that the Greek poet Aeschylus died because a bird mistook his bald head for a stone and dropped a tortoise on it. This proposition is further supported by our current observations of birds dropping shellfish on stones in order to crack their shells. So clearly it is possible to damage a (fairly low mass) shellfish by dropping it on to a hard surface. The terminal velocity of a tortoise, of, say, ten to thirty centimetres diameter, is going to be a lot less than that of a falling bullet of 0.5 to 1cm in diameter. This is because the air resistance of a falling object varies as the cube of its cross-sectional area, I think - I know it has something to do with the Rayleigh Number, but gosh, I'm not sure what that is. Anyway, we now have something falling from a great height. Because it has fairly small cross-sectional area it won't be impeded much by air resistance, so its velocity will increase as affected by gravity. The kinetic energy of a moving body is proportional to its mass, but also to the square of its velocity. So the energy of a falling body is likely to be greater for a body of small cross-sectional area (like an edge-on coin) than for one of the relative size of, say, a tortoise. This is why regulations were introduced to bar passengers on trains crossing the Forth Bridge from throwing coins through the windows. The edge-on coins were embedding themselves in the decks of ships passing under the bridge. You don't need the Empire State Building - try it for yourself from a suitable high location. Umm... just realised, British pennies (LSD, pre-decimalisation) were something like six to ten times the weight of an American cent, so it's denarii we're talking about, not US cents.