# Why did he spin the egg before throwing it?

I’m bored cooking and eating an ordinary omelette so I try to search some videos about how to cook an omelette in youtube. Somehow I stumble on this video

Watch it! The rest of this post is pointless if you don’t watch it

I assume you already watch the video, so now you understand the title of this post. Okay let’s discuss about it..

First, we know that his goal was to cut the egg. In more detail, he wants the egg to be in horizontal orientation before hitting the rectangular knife(or rectangular what?). The orientation of the egg is described by the vector pointing from the “blunter” end to the “sharper” end. And let’s call everything inside the egg with the word “fluid”.

When the egg is spinning the centrifugal force pushes the fluid to the ends of the egg, blunt and sharp.  So Perhaps he spin the egg because he didn’t want to cut the yolk at the center of the egg? NO! I hope the purpose must be something much cooler than that, so let’s assume that this is not his goal.

Another possibility, he made the egg spinning about the vertical axis so that it becomes more stable against perturbation and more likely to remains in horizontal orientation. It’s much easier to throw and catch a stable egg. And he also needs to spin the egg for a long time because the fluid inside and the shell are not quite coupled, the friction between them is very small.

Yet another possible advantage… if we spin the egg around the vertical axis, it makes the egg harder to move in a straight line. It’s common sense! you can imagine it! Because when the egg is moving translationally it is also rolling, when the orientation change due to the rotation the egg still preserve it’s rolling angular velocity. Consequently the egg tends to move in a circle, the radius of the circle depends on the velocity of egg’s center of mass, in other words it makes the egg harder to move in a straight line. So what if the egg is harder to move in a straight line? Of course it’s very helpful! It’s very hard to throw an egg properly if it can rolls easily from the rectangular tool(or what?), it’s much easier to control when the egg is spinning.

But the pan and the rectangular tool is very oily, it hardly rolls at all, it might simply slide without rolling.. You can see that when the awesome guy was spinning the first egg, it’s clearly shown that the egg moved through a curve path. That means that the friction is significant! I also tried putting an egg on an oiled frying pan and then I tilted the pan. It turns out that although the pan is very slippery the egg was still rolling through it’s way down. But actually my egg is pretty rough, maybe his egg is not as rough as mine…

Maybe the last theory is right, but the guy’s hands are also very talented, I think he can balance the egg just by tilting the rectangular tool rapidly. I hope one day I can meet an omurice cook and ask him about the reason…