system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What stops the first kernel of popped corn from burning until the last kernel pops?

The last kernel being the one you feel safe stopping the microwave at, without burning the entire bag.
gpt
Microwave ovens heat food by exciting water molecules: the radiation gets absorbed by water most readily, and tends to pass through most other food bits pretty easily.

Unpopped popcorn kernels contain little bits of water inside that are heated, boil off into steam, and burst out of the kernel, forming the popcorn itself and allowing the water the escape.

While the first popped kernel sits around waiting, microwave radiation is passing over and through it and getting absorbed by other water molecules in other kernels, causing almost no damage to the first kernel at all.

It's not until all the popcorn has been popped that very little concentrated amounts of water remain in the whole set of popcorn, so the microwave radiation starts getting absorbed more readily by the fleshy bits of the popped popcorn kernels. That's when they start to burn, and it's before that point that you want to stop the microwave.