I was walking over the Kingsgate Bridge one morning in October 1995 when my companion and I wondered how high it was. Without another word being spoken, he dropped a coin over the bridge and we timed the descent. Continuing the walk, we did the maths between us and estimated it to be around 70 ft above the water. It was only later that I saw this as the moment in time at which I became a physicist.
Fast forward to yesterday. Making the same journey with a different friend, I wondered aloud what the volume of a McDonalds drinking straw was. We chose a radius of 1/π cm and a length of 5π cm, thus the capacity was 5 ml. He tells me that multiples of π is a physicist’s approach!
My point? Even when you think you've left your degree firmly in the past, it can still rear out of the back of the brain and surprise you.