Please note: You are viewing the unstyled version of this website. Either your browser does not support CSS (cascading style sheets) or it has been disabled. Skip navigation.

# Sidcot Questions 1-3 Mug of Tea Heat Loss Experiment

## Answered by Ben Harden, Outreach and Meteorologist

 Print PDF

Enlarge Image

Tea temperature vs. Time graph (Ben Harden)

Related Multimedia
 Tea Experiment photos » View Slideshow

The experiment has been conducted! One cup of tea was left out on deck, with an ambient temperature of about 2 degrees centigrade, and the other was placed in a -15 degrees centigrade freezer. Both had their temperatures monitored for an hour and the graph shows the results. The measurements from the cup left outside is shown in black and those from the cup in the freezer in blue. The dashed lines show the ambient temperatures for both experiments (i.e. the temperature we would expect both cups of tea to become given enough time). I have fitted some simple exponential curves to the data, it should be that the temperature of an object which is hotter than it's environment will reduce exponentially until it reaches the temperature of it's environment.

Some interesting effects can be observed. Firstly, the cup left outside cools much faster than the cup in the freezer even though the cup was in a warmer environment. This is because it was a windy day out on deck. Just as you might blow on a cup of tea to cool it, the wind cooled the tea by evaporative cooling - the energy required to free water molecules from the surface and turn them in to a gas is extracted from the heat within the tea. Evaporative cooling occurs even when there is no wind, but it is extra strong when there is wind.

The cup in the freezer cools steadily following an exponential curve for most of the hour. Near the end of the experiment, the temperature of the cup becomes warmer than the fitted curve. This is because the tea is about to freeze. As the molecule in the water begin to enter the solid phase, they release the energy they had in their liquid phase in the form of latent heat. This will keep the tea at around freezing temperature until all the molecules have fused to form a block of solid tea. After this the temperature would then begin to reduce again until reaching equilibrium with the environment (in our case -15 degrees).