The Boyle-Mariotte Law is a law of physics that divers should know. It says that the product of volume and pressure always remains the same for gases. This means that in case of increasing ambient pressure (so under the surface of water) the volume must diminish. The rule of thumb is: Double pressure – half the volume.
Practical application of the Boyle-Mariotte Law
A practical application of this law is the construction of the first depth gauge. In doing so, a thin tube was used, which was pressure resistant, made of glass for instance. On one side, this tube is tightly closed. On the other side, the tube is made water resistant with a movable plunger. The higher the ambient pressure, the further the plunger is pressed inside. That way the depth can be deduced on the basis of the ambient pressure.
Modern depth gauges are computer-controlled though, because the mechanical systems were very error-prone and were inclined to get dirty.
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