The truth is revealed: Stirring tea doesn’t cool it faster

Yesterday I finished the book: “What If?: Serious Scientific Answers to Absurd Hypothetical Questions”. The book is written by a physicist who used to work for NASA who decided to quit and start drawing comics on his website If you are a nerd you are probably familiar with the site.

Few of the answered I liked were “Can I create a jetpack using downwards pointed guns?”, “What happens if a woman self fertilizes her egg with a sperm carrying her own DNA?”. The latter one was more interesting as I finally learned why relatives marriage might result in retarded kids, and why genetic disorders such as the one I have which resulted on not being able to walk has a 50% chance of passing down to every kid.

Yet, the funniest one which I should shock my dad was about, if you stir tea, will it cool down faster? Short answer is NO.

The physical effect of stirring is actually a little complicated.[6] Most of the heat is carried away from teacups by the air convecting over them, and so they cool from the top down. Stirring brings fresh hot water from the depths, so it can help this process. But there are other things going on — stirring disturbs the air, and it heats the walls of the mug. It’s hard to be sure what’s really going on without data.

Fortunately, we have the internet. StackExchange user drhodes measured the rate of teacup cooling from stirring vs. not stirring vs. repeatedly dipping a spoon into the cup vs. lifting it. Helpfully, drhodes posted both high-resolution graphs and the raw data itself, which is more than you can say for a lot of journal articles.

The conclusion: It doesn’t really matter whether you stir, dip, or do nothing; the tea cools at about the same rate (although dipping the spoon in and out of the tea cooled it slightly faster).

You can read the whole answer here, where you will find out if you can boil a cup of water by stirring very quickly.

If you have great book recommendations feel free to add them as comments. All things non-fiction are welcomed.