In the Spirit of Easter which is almost over but Happy Easter for anyone who celebrates. And Happy Passover to anyone who celebrates as well. But the topic is: egg tapping at easter. My boyfriend and I had an argument about what makes the eggs break and how we can optimize. I said force, he said impulse, so we emailed our physics teacher and he had the best response ever HE EVEN CITED SOURCES. I am cutting out the beginning because he just roasted my grammar and called us awesome nerds but here is explanation for anyone who wondered, probably none but hey
“The simplified rule of thumb is that it is force, not impulse, that causes things to break (simple experiment: you can easily break an egg by holding it with two fingers and squeezing, which imparts zero impulse), but the details of how things break is actually really complex! Forces applied to an object or material tend to cause it to flex or deform. In this context, the distribution of forces is called stress and the deformation is called strain. Ignoring fatigue, which causes materials to weaken under repeated or prolonged strain, an object will break once it has deformed past a certain point. Some objects are brittle, which means they can't withstand much deformation, while others can deform a lot before breaking. But a brittle material can still be hard to break - brittle means that it will break before it deforms substantially, but it might take a great deal of stress to cause it to deform much in the first place. For example, cast iron is very brittle, but can you imagine tearing or snapping a cast-iron pan in half with your bare hands? Conversely, consider the plastic that disposable water bottles are made out of: very little stress will cause a substantial strain, so even though this plastic can deform more before it breaks, it's probably much easier to break than cast-iron (in certain circumstances).
Anyways, back to egg fights. Egg shells are both brittle AND weak. Even a relatively small force will cause an egg shell to deform, but because they're so brittle, they'll break first. This image from the wiki page on stress shows the many different kinds of stresses. Surprisingly, two of them are relevant to the case of colliding eggs. The obvious one is bending: when two eggs collide, they will push into each other, causing the shells to flex inwards and bend until they break, or the resulting elastic force causes them to rebound (unlikely, in this case). But as Kate mentioned, the angle of the eggs does matter. Imagine the two big eggs in this image collide in the orientations shown. The black one is less likely to break than the white one, and we can see why with a little thought experiment.
Consider a thin, flat sheet of eggshell (maybe it was laid by a 2D chicken). Secondly, consider a spherical, hollow eggshell (laid by a chicken so traumatized that it's empty inside, perhaps). If you were to poke each of these things, you can probably imagine that the sheet would be more likely to break. Poking the sheet will cause it to bend (refer back to the chart of different kinds of stresses). Egg shells are particularly weak to bending, and so it will break easily. On the other hand, when you poke the spherical shell, you'll cause some bending, sure, but also compression! Assuming you poke with the same force, that means some of that force causes compression, and so only a part of the total force is available to bend the shell. On top of that, it takes much more force to compress egg shell material than it takes to bend it (it's important to understand that compression, in this case, means, for example, taking a square sheet of shell and trying to squeeze it into a rectangular shape; it might be hard to visualize how this works for a 3D shape like an eggshell, but try!). This is why it's easier to break an egg by squeezing it around its middle, vs. squeezing across the poles. The part of an eggshell around its middle is pretty flat, so when you squeeze it there you're mostly just bending it. On the other hand, the part of the shell at the ends is much more curved, and so your force is causing both bending and compression stresses.
To understand better why it can't really depend on impulse, imagine carrying an egg onto an airplane. The average cruise speed of an airplane is about 250 m/s. As long as you're careful, there's no reason why the egg shouldn't survive. Now imagine throwing an egg into a wall at 250 m/s. It will definitely break, even though the impulse is the same. And that's because the forces accelerating the egg on the airplane are small, and so the stress on the egg at any point is small. But when the egg hits the wall at full speed, it experiences a huge stress over a very small period of time, and it breaks.
TL;DR for the most part, it is the stress (forces) on an object that cause it to break. For the most part. How long an object is under stress does actually matter, too, but that's much more complicated and not really needed to resolve this particular debate!
Also, there are a surprising number of published papers published about this sort of thing. This paper from the journal of British Poultry Science (who'd've thunk that would be a thing?) appears to indicate that the weakness of eggshells to tension is a major factor in their breakage, but unfortunately, I can't access the whole paper. Kind of makes sense, though: as the shell bends inwards, the shell stretches.”
And the award for best AP Physics teacher goess tooo....
P.S. He is actualy rad af and he loves elephants so if anyone has any elephant gifs plz send me them
