Dear Evil Engineer: Can I throw an egg so hard it cooks on impact?

Dear Aunt Linda,

How are the geraniums? It’s very bright and sunny here in Margate and I hope you are also having lovely weather. Spring seems to have come early this year. I wonder if we are due to have yet another unprecedented heatwave this summer!

You know how it is when summer comes in Britain. The small talk is all about how it’s so hot that the tarmac would melt, or that you mustn’t walk your dogs during the day, or that you could fry an egg on the pavement. Well, I was wondering if it is really possible to fry an egg on a pavement? Or – here’s a thought – is it possible to throw an egg on the ground so hard that it cooks on impact? Maybe you would have the answer, being the best cook I know! No one will ever beat (no pun intended!) your parmesan poached eggs.

Send plenty of hugs and kisses to the cats.

Your loving nephew,

Jim

Dear Jim,

Something about this letter makes me suspect that it was not intended for me. However, having gone so far as to open and read it, I feel that I have the responsibility to answer it to the best of my ability.

In response to your first question, the geraniums are very nice, thank you.

Now on to your second question, which concerns whether it is possible to fry an egg on a really hot pavement. Let me start by explaining in very simple terms what happens when an egg is cooked. Initially, the proteins in the egg are folded up in bundles, which interact with each other very little. When heated, these proteins denature (unfold out into charged strands) and coagulate (connect with each other to form a clump). Through this process, the surrounding water is squeezed out and evaporates, leaving behind a stiffened egg. Obviously, these changes require energy input: eggs start to cook at around 70°C.

According to Robert Wolke’s 2002 book ‘What Einstein Told His Cook: Kitchen Science Explained’, pavement temperatures vary depending on factors such as material, exposure to sunlight, and ambient temperature. Though I stumbled across reports of pavement temperatures in Saudi Arabia as high as 72°C, Wolke asserts that pavements tend not to get hotter than 145°F (63°C). Even if global temperatures continue to rise and, by 2150, pavements are regularly heated to 70°C during summer, there would still be no guarantee that you could fry eggs on them. Most likely, you’d end up cooling the pavement while cooking the egg fractionally and unevenly.

Wolke suggests that car bonnets make more appropriate makeshift frying pans – and this has been demonstrated with some success.

Onto your third question, then: how about giving the oeuf a little oomf by slapping it on the ground really, really hard?

This is a different heating mechanism entirely. Rather than the gradual transfer of internal energy (‘heat’) from hot ground to less-hot egg, it relies on the rapid transfer of the egg’s kinetic energy to internal energy on impact with the ground. To determine whether it is possible to cook an egg using this approach, let’s find the speed at which the egg contains enough kinetic energy to cook itself through, and see how silly it sounds.

To start, we must work out how much energy is required to cook an egg. Let’s use a simple model, in which the shell contributes 10 per cent of the total mass, the yolk 30 per cent, and the white 60 per cent. A medium egg weighs 60g. So, that’s 6g of shell, 18g of yolk, and 36g of white. According to a 2015 paper in Food Science & Nutrition, the specific heat capacities of these substances are 888 J/kg°C, 3,120 J/kg°C, and 3,800 J/kg°C, respectively. If we want to heat the whole egg from room temperature (21°C) to cooking temperature (70°C) that’s an increase of 49°C. Plug these figures into the heat capacity equation Q=mcΔT, calculating mc for each element of the egg and summing them: Q= (mcshell + mcyolk + mcwhite) ΔT = (0.006x888 + 0.018x3,120 + 0.036x3,800) x 49 = 9,716 J.

Putting our figure into the equation for kinetic energy, we find that a 60g egg would have to be hurled towards the ground at 569m/s to contain equivalent energy. That’s nearly twice the speed of sound. You could say that it is... ‘eggcessively’ fast.

Ridiculous as this speed is, it is only a lower bound. Not all kinetic energy is turned to thermal energy: some will be lost as sound, some as heat transferred to the ground, and some will be consumed in smashing the egg – and, at those sorts of speeds, probably the pavement too. There may be an aerodynamic heating effect that offsets these losses slightly but, in all likelihood, your egg will need to be travelling significantly faster than 569m/s to be cooked on impact. If, for instance, you could find some way of adapting a .220 Swift (muzzle velocity 1,422m/s) to fire eggs at the ground, perhaps you will be able to scrape something edible from the impact crater in the tarmac.

Yours,

The Evil Engineer

PS: Despite surface temperatures not creeping high enough yet to fry eggs, interest in the idea shows no sign of abating. For instance, every 4th of July there is a ‘Solar Egg Frying Contest’ held in Oatman, Arizona – the combination of low humidity, high temperatures, and permitted use of mirrors, reflectors, magnifying glasses, and other optical instruments to focus sunlight makes it less of a fool’s errand than one may expect.