A simple answer would be to stop hitting your fingers with hammers and just leave it as one of life's little mysteries (silly boy
), but as a keen scientist myself I thought I'd look into this.
It seems that it's all to do with the temperature of the hammer. When it is cold the hammer is at it's most dense and thus causes more damage to your poor wee nerve endings. Add to that the psychological factor of it being cold in the first place - nothing good ever happens when it's cold, apart from skiing holidays and you're hardly likely to be using a hammer on the piste- Instead your brain is going to be feeling insecure and sensitive like the weight of the world is on it's shoulders. A hammer whack to the thumb will just make it want to curl up in a corner and cry like a five year old who's just popped a favourite balloon.
Conversely if it's hot, the density of the hammer will be a lot less as it will be closer to the solid/liquid transition zone. This will greatly cushion the impact and seeing as it's hot and sunny, the odds are, you're probably on a beach somewhere with a cool drink close by, getting blown. Sore thumb? Get real says your brain, it's Mojito time...
In conclusion, like most of life's important questions, it's all a mix of Psychology and Thermodynamics
