A diver feels a clear pressure change after descending only a metre in a pool, while a lift ride of many storeys produces only a slight change in air pressure. Which fact explains the contrast?
AAir is about 775 times denser than water
BWater and air have about equal densities
CAir pressure does not vary with height
DWater is about 775 times denser than air
Answer & Solution
Correct answer: D. Water is about 775 times denser than air
1. Pressure due to the weight of a fluid is proportional to both depth and density.
2. Water is much denser than air, about 775 times as dense.
3. One metre of water therefore produces the same pressure change as hundreds of metres of air.
4. So a small dive is felt while a tall lift ride is barely noticed.
5. Saying air is the denser of the two reverses the physics, and air pressure certainly does fall with altitude as the weight of air above decreases.
_Source: OpenStax College Physics (CC BY 4.0), Ch 11 "Fluid Statics", section 11.4 Variation of Pressure with Depth in a Fluid_
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