Kettles, pots and metonymic shifts….
As our Departmental Christmas lunch is looming I only have time for a brief reblog of this nice discussion of boiling water in pots. It might strike you as as a bit obsessive to write about the physics of such an everyday phenomenon, but I think a bit of an obsession about physics is a very good thing indeed.
P.S. As a fully paid-up member of Pedants Anonymous I couldn’t resist drawing attention to the metonymic shift involved in the title “Watching pots boil”. Of course the pot doesn’t boil – the water in it does….
My previous article about kettles left me wondering: Can gas hobs really waste more than half of the calorific energy in the gas? I decided to try a few more experiments and finally I think I have an answer: ‘Yes’. Gas hobs really do fail to transfer a great deal of the calorific energy in the gas to the pan or kettle they are heating.
Experiment#1 Rather than measuring the total time to reach 100 °C, I measured the rate of temperature rise. Because the heat capacity of water is well known, this allowed me to estimate how much thermal power was entering the water. So I spent a happy hour or so heating up various amounts of water: first 200g, then 400 g, 600g and finally 800g and I measured the temperature every 20 seconds.
I knew the burner power was 1.75 kW, and after a little jiggery pokery with a…
View original post 639 more words
In the Dark 
December 17, 2012 at 10:19 am
I don’t think he took account of evaporation, which makes a significant difference.
December 28, 2012 at 8:34 pm
I don’t think he took account of evaporation, which makes a significant difference.
I did. I looked at the warming rates from 20 C where vapour pressures are low. When I tested the time to boil I used glass lids. M