The Physics of ... a Dog's Life

Our dog never seems happier than when she gets to lie in the sun, and who can blame her. It's a welcome break from her usual hard life of lying in her bed, or walking on the beach.

And having recently come into ownership of an IR thermometer, i decided to try to evaluate the comfort that the sun provides.

The thermometer I have is this: ATP - Laser Infrared Thermometer - Battery Included - [AI-IR-801]

The first thing I did when I got it was to point it at myself, and I was a little dismayed to find my temperature to be 31 oC.

Did this mean that I was either (a) very unwell and possibly deceased, or (b) the thermometer wasn't working.

It turned out to be (c) - both me and the thermometer are fine. It describes itself as 'ideal for non-contact measurement of surface temperatures' - and of course our surface temperatures are considerably lower than our internal 37 oC. There are also clinical IR thermometers which are programmed to calculate our body temperature from that surface information, but this one doesn't - and is perhaps more interesting becasue of that. I played around with it and found that areas unprotected by thick bone give higher readings than, say, my skull. Holding it to my open mouth gives a reading 36 oC, for example.

So having satisfied myself that the device is working (and that I wasn't deceased), I set about investigating the dog and as this was on a sunny morning, I knew where to find her. And what I found was interesting. Pointing the device at a shady area of the floor, I found - as shown below, that it was 19.8 degrees. Whereas in a sunny spot, it was 24.3 degrees. I can see why that extra 4.5 degrees is attractive to the dog. A nice heated surface on which to recline. Converting our kitchen floor into something like a dog-spa.

But then it occurred to me that as she's lying there, the floor is no longer getting to absorb all those sunny rays. And instead it's her black fur that is doing so. And being black, she is almost designed to do so efficiently. So I pointed the thermometer at her fur...

40.5 degrees! It's no winder she loves it there. Soaking up all the heat. But also its no wonder that every now and then, she rouses herself and wanders over to her shady bed to cool down.

I plan on carrying this thermometer around with me for a while, seeing what else I can learn. I'll keep you posted!