Things children say

The only-begotten children have grown up in an atmosphere of concentrated geek so they have had a…non-standard vocabulary from early on. One of my favourite stories is from when the only-begotten son was perhaps three years old and I was taking him home from daycare in his stroller. Leaning back he spotted an airliner passing overhead and asked:
“How many neutrons are there in that plane?” [Well, it was more like “newtyons” as he couldn't pronounce “r”.]

I realised that for a change this actually was an answerable question, even if I had to look up a few things first. An Airbus 320 has an empty weight of about 42 000 kg, say that as it was on the finale towards Arlanda it would have weighed something like 60 000 kg with passengers, cargo and fuel. It is mostly made of composites and aluminium, i e mainly elements with as many neutrons as protons in the nucleus, so we can take half of the mass to consist of neutrons (that have a mass of 1.67×10^-27 kg). In other words the number of neutrons would be 6×10⁴/1.67×10^-27/2 ≈ 2×10³¹.