By: Blonde Two

Here are a couple of scenarios that lovers of the outdoors will recognise…

  1. It is autumn. You roll out your bivvy and sleeping bags and realise you have forgotten your sleeping mat. Despite it being a relatively warm night, especially inside your cosy down sleeping bag, you have a poor night’s sleep because the ground underneath you is cold.
  2. It is autumn. You arrive at the beach in the rain. You strip off and feel immediately chilly as the rain drops hit your skin. You get into the water and, after the initial splashes, you realise that you feel warmer in the water than out of it.

Have you ever wondered why that happens? Why is the ground colder than the air and how can the sea possibly feel warm when there are so many cold raindrops falling into it?

Warning… I am about to attempt physics for the second time in seven years…

Both of these phenomena could be due to the hysteresis effect whereby a system’s response to changes depend not just on its current state but also on its history. In simple terms this means that when the sea has been warm all summer, it will take longer to cool down than the air will. It also means that, although the air can be heated up quickly by the sun, the ground is used to being chilly and won’t respond with any amount of speed.

I am still trying to get my head around this but am convinced that hysteresis is a thing in outdoor life. You might be interested to also know that when people design computer systems to interact with humans they often build in hysteresis to help us keep up.

Which is just as well!