why does popcorn seem to pop at a somewhat consistent rate regardless of the amount, instead of all of them popping closer to at the same time?
In: Physics
Similar reason to why the temperature of boiling water stays at 100C. At a certain point, energy into the system causes water molecules to evaporate, instead of raising temperature, no matter how much you have.
This is probably a similar system where heat put in results in pops instead of a raise in temperature. Put in heat at a constant rate, you get pops out at a constant rate, no matter how much you have.
It’s been a long time since I’ve popped popcorn, but it seems to me that you get one, then a pause, then a second one, then more, then a long stretch where they’re popping fast enough that you can’t really tell, and then tapering off to longer and longer pauses between pops. So, a normal distribution (or close to it) with low deviation.
I haven’t really checked it, but here is my intuition:
It takes about 400x more energy to boil/evaporate water than to heat it by one degree.
Since you need to evaporate water for popcorn to pop and energy is limited in vast majority of cases (such as being heated from the bottom), the popping rate will be limited by how much power is used.
There are small differences between kernels, its almost impossible to heat them all uniformly. Therefore your rate will be: power/(energy to pop a kernel).
Consider a pot with a layer of oil and popcorn on the bottom. When you apply heat, it goes into the oil which heats the kernels. Since the oil distributes the heat fairly evenly, all the kernels are being equally heated. However, things change dramatically when a kernel that’s just a little hotter than its neighbor explodes.
When a kernel explodes, it does so because the water inside is expanding to steam. That takes heat out of the local region, that is, the exploding kernel cools the surrounding kernels.
The heat required to vaporize water is about 540 calories/gram of water. That heat comes from the surrounding oil and kernels. But there’s a lot of oil and popcorn so a kernel elsewhere in the pot isn’t affected by the explosion as much as the immediate neighbors so it pops as well. So now you have two cooled spots, the first warmer than the second because the heat is still being applied. The next hottest spot pops a kernel and cools and the cycle continues until all the kernels have vaporized the water inside of them.
So basically what’s happening is the pot is alternating between heating and cooling regions of the pot.
kernels packed tightly together, until the outer ones get the heat transfer first and then pop, sending other kernels flying or allowing them to fall to the front, then they start to pop off until only the most center kernels are left
There is bigger and smaller corn and different positions. Some have a tougher outer layer some softer.
2 primary reasons assuming all kernals are of nearly equivalent size, which popcorn companies try really hard to do.
1) when a kernal pops the water inside the kernal flash boils and turns to steam. The phase change from liquid to gas absorbs heat and cools the area around it.
2) the container the kernals are in heats from the outside in, so the kernals on the perimeter will get hotter faster.
All these arguments about different kernal-wall/layer thickness and water content doesn’t really hold up. These are micrometer and picoliter differences that matter little when blasted with 1200 watts of radiation.
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