Some simple physics reveals the most efficient way to cool the coffee you'll be spitting out in exasperation
If, like many people in this time zone, you stayed up early into the hours of November 9th, only to discover that 2016 decided to really stay on brand, chances are you’re pretty tired by now. In moments of political and existential exhaustion, many turn to coffee to refuel their hazy way through the fugue and turmoil of the morning. And then you take a sip and burn your tongue, adding injury to insult. But never fear, physics has figured out the best way for mourning Americans to cool their morning Americanos.
Over on Wired, Rhett Allain carried out an experiment to determine what is the most efficient way of avoiding a gritty tongue for the rest of the day. Allain took three paper coffee cups and filled them with boiling water, leaving one with its lid on, another with its lid off, and the third with its lid still on, but into which he sporadically blew to cool the liquid inside.
Perhaps unsurprisingly, the lidless cup proved the safest bet. Explaining the science, Allain points out that there are two ways in which heat can be lost – conduction and evaporation. In the first, putting the hot coffee close to something cold sees the thermal energy leech away. While the air around the coffee cup and the work surface on which it stood were colder than the water inside, it wasn’t sufficiently colder enough to have an impact on the temperature of the coffee.
But on the cup without a lid, evaporation sees water escaping from the surface of the coffee, leaving behind water molecules with less energy and lowering the temperature. Without the lid, there is a much larger surface area from which the heat can escape, although blowing across a lid’s hole can also help.
So order a double shot and face the new world order with the lid off – at least you won’t burn your tongue.