1. Twice as warm

Our son, who is an actor has just come back from a 3-month tour and this week he moved into a new flat in south London. So, very early last Sunday, Sheila and I filled the car with possessions that he had been storing in our spare bedroom and set off for London to help him move them in.

The first thing we noticed on stepping out of the car was the temperature in London that morning – decidedly brisk. Leo was waiting to greet us outside the modern, red-bricked, 6-storey apartment block. ‘Top floor, Leo’ I asked, joking. ‘That’s right.’ Leo replied, but unfortunately he wasn’t joking!

Returning to the Midlands that afternoon Sheila remarked, 'It's twice as warm here as it is in London!' But is it really possible for one temperature to be twice as warm as another? We keep a thermometer in the garden. It is marked in Celsius down the left side and Fahrenheit down the right and the reading was 10ºC. 

The garden thermometer

I googled the weather details for that day and the temperature in London had been 5ºC. 

So Sheila was pretty pleased to hear this information. 
'Just as I said – twice as warm here as in London!'

But temperature is one of those funny measures where it doesn't make sense to talk about 'twice as warm', 'four times as warm' and so on. The evidence is revealed when you shift to a different unit of measure – say to the Fahrenheit scale. We looked closely at the two scales side by side. 

Celsius on the left, Fahrenheit on the right

When using the Celsius scale on the left, 10º was twice 5º. But coming across to Fahrenheit, the two corresponding temperatures were 50ºF and, roughly, 40ºF. Clearly these two readings did not share the same pattern: 50 is not twice 40.

Anyway, that's measurement for you. I'll end this post on a 'light' note with this little rib-tickler.

Postscript

So, when comparing two temperatures there's no such thing as 'twice as warm'. The same issue crops up when talking about time of day – you can't sensibly talk about 'twice as late'. But you can talk about 'twice as far', 'twice as heavy', twice as many', etc.
If you are interested in finding out more about measuring scales and their properties, you’ll find an explanation here in my website, MathinPictures.co.uk.