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While we’re at it, 20000 leagues under the sea is the distance they travelled, not the depth
You can go much deeper than 10 fathoms without supplemental oxygen, half the people reading this right now could do it with some training.
The world record is 117 fathoms on a single breath.
It’s 6 fathoms deep not 5 fathoms where you’re experiencing two atmospheres, and that’s absolute not gauge, so 1 atm higher than ambient.
Retard units at its finest. Why simple when it can be difficult.
For every 10 meters of water, hydrostatic pressure increases by one atmosphere
Wood Hole Oceanographic Institution
For every 33 feet (10 meters) of saltwater depth, pressure increases by another atmosphere.
It’s less the result of a sensible system of units (like how 1 L of water ideally weighs 1 kg), and more fortunate happenstance in this case.
The formula for hydrostatic pressure* is:
∆P= ρ·g·∆h
where ∆P is the difference in pressure across the difference in height ∆h, ρ is the density of the liquid (~1000 kg/m³ for water, slightly more for sea water), and g is the acceleration due to gravity.
So the reason it works out nicely is because g is a little bit less than a nice factor of ten (9.8 m/s²), and the density of sea water is a little bit more than a nice factor of ten (typically 1025 kg/m³), and 1 atm also happens to be almost a nice factor of ten (101,325 Pa). That’s why the difference between the approximation and the actual* is less than a percent.
*This assumes a constant density of the liquid, which for water is reasonable, however different depths can have different salinities and temperatures in layers which change the density by less than a percent. Additionally, this assumes a constant acceleration due to gravity. At depth, the acceleration due to gravity can be higher, but this also has an effect that amounts to less than a percent even at the deepest point in the ocean.
