Rain
Today we were comparing the sound of two rainstorms, one having sounded like rain, and the other (less intense) as if it were hail, but turned out to be rain.
Which left me contemplating whether a raindrop will always reach terminal velocity before it impacts the ground, and contemplating the impact of raindrop volume on relative weight, which left me with one of those person "d'oh I'm an idiot" moments when sluggish brain recalled that of course it would, as weight=mass x gravity. So in all likelihood the reason why the second rainstorm sounded like it was heavier despite not being as intense was because the drops were bigger.
I'm sure that part A of my brain being able to make part B of my brain feel really embarassingly dumb is a very -special- skill.