How do you like your toast?
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Understanding cooling
Hot toast cools down quickly. There are two reasons for this.
- First it cools down because it is hot! All hot things cool down by transferring heat to their surroundings. The heat in the toast is transferred to the surrounding air.
- It cools down quickly because a slice of toast has a large surface area compared to its volume. There is a large area of contact between the surface of the toast and the surrounding air. The hot toast loses heat to this air, which rises and is replaced by cooler air; which is in its turn heated by the hot toast. In this way the heat in the toast is quickly transferred to the air and the toast drops in temperature.
Imagine if the toast could be rolled up like a sponge roll. The amount of surface exposed to the air compared to the volume would now be much smaller and the toast would take longer to cool.
Think how your tea or coffee stays hotter longer than your toast even though the surface of your toast when it came out of the toaster was much higher than the temperature of your hot drink. The hot liquid has heat trapped inside with the only way out through the surface and the surface area to volume ratio of the hot drink is smaller than for the toast.