Can this issue make us ponder? Certainly! We bring a glass or spoon of water to our lips and “slurp” the liquid contained within into our mouths. This simple action of “slurping”, which we are so accustomed to, actually requires an explanation.
Why does the liquid flow into our mouth? What draws it in? The reason is this: When we drink, we expand our chest, thereby reducing the air pressure in our mouth. Under the influence of the external air pressure, the liquid tends to flow into the space with lower pressure, and thus it flows into our mouth.
The phenomenon here is similar to what occurs with liquids in interconnected vessels. If we reduce the air pressure above a container, the liquid will rise within that container due to atmospheric pressure. Conversely, if we tightly seal our lips around the neck of a bottle, no matter how hard we try, we cannot “slurp” water from the bottle into our mouth, because the air pressure in our mouth and on the surface of the water is the same.
Therefore, to be precise, we do not only drink with our mouths but also with our lungs, as the expansion of the lungs is what causes the liquid to flow into our mouth.
