Xkcd webcomic writer and science communicator Randall Munroe has written two books on what he calls "absurd hypothetical questions". Among the unusual questions explored in his first What If? book was this: “From what height would you need to drop a steak for it to be cooked when it hit the ground?”. Munroe gave a pretty comprehensive answer but also pointed out that a lab experiment would be needed to check his “wild guess.” Well, now that experiment has been done – and there is footage.
The question by Alex Lahey is based on the fact an object moving at high speed through the atmosphere will experience tremendous heating due to air compression on the leading edge. So would it be possible to cook a steak that way? Well, not really. Despite the high heat, it is a terrible way to cook one.
An example of why is what happens frequently when meteorites get to Earth. Their outer layers are heated up and burned off, so what actually reaches the ground is cold. The same thing happens with the steak. Munroe hypothesized that the outer layers would get seared and be ripped off at high speed. For a steak mooing at Mach 5 – five times the speed of sound – the compression will sear it and squish it, but the inside will stay raw.
“For the sake of this simulation, I assume that at lower speeds some type of vortex shedding creates a flipping tumble, while at hypersonic speeds it’s squished into a semi-stable spheroid shape. However, this is little more than a wild guess. If anyone puts a steak in a hypersonic wind tunnel to get better data on this, please, send me the video,” Munroe wrote in the answer.
Turns out, somebody did just that. Tom Fisher and Thomas Rees were researching hypersonic heat transfer at the University of Manchester, UK, and decided to conduct the experiment. They used a “21-day matured beef steak” from British supermarket chain Sainsbury and placed it in a wind tunnel at Mach 5.
Munroe’s approximation of the squishiness was not too far off and it can be clearly seen in the Schlieren imaging showing the hypersonic winds. The thermal cameras show how the exterior of the steak is indeed seared and blown off, while the interior stays cold.
It is always good when the experiments match the theories.