Tuesday, March 22, 2016

Good to Know!

Have you ever wondered how long it would take for a vampire to drink all of your blood? If so, a group of science students with too much time on their hands at the University of Leicester claim to have figured it out. According to their calculations, it would take a little under six and a half minutes to drain 1.3 pints of blood - and at least forty-two minutes to drain a human body completely.

To make their calculation, students at the University of Leicester used fluid dynamics to estimate how long it would take for the blood to flow out of a hole in the carotid artery.

They assumed the external carotid artery itself would have a diameter of 0.2 inches (0.5cm) and calculated the speed of the blood flowing into it travels at 1.34mph (0.6 metres per second).

They then calculated the pressure difference should a hole be punctured into the artery by comparing the average human blood pressure in arteries to air pressure. By factoring in the density of the blood at room temperature, they calculated that the blood would leave the puncture wound at 11mph (five metres per second).

The students also assumed their fictional vampire's fangs would leave puncture holes just 0.02 inches (0.5mm) wide and factored in the density of the blood at room temperature.

They performed the calculations to coincide with the 85th anniversary of Tod Browning's 1931 horror film Dracula starring Bela Lugosi.

Now I'm not a vampirologist or whatever it is they call themselves, but even I can see the problem here. These calculations assume that the vampire doesn't suck - which, of course, everyone knows they do, in more ways than one. So comparing the pressure of blood in the carotid artery to regular air pressure will yield a value that's too slow. Still, movies and television programs often show vampires draining their victims in a second or two, which is unrealistic even if they can create a perfect vacuum.

Maybe Anne Rice had it right all along - vampires can drain their victims almost instantly because they have super-speed relative to everything else in the world. But could that effect really extend to the speed at which they can extract blood from their victims?

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