Why doesn't a bag of popcorn pop all at the same time?

The reason why a bag of popcorn does not pop at the same time is very simple. there are millions and millions of tiny particles in the kernels and in the oil. some of these particles absorb more energy faster than others. these kernels will be the first to pop and may burn if left left in contact with heat. the last kernels to pop are probably the biggest and therefor they take the longest to heat up