Underwater Pressure

on . Posted in Fluid Dynamics

Underwater pressure, abbreviated as \(p_u\), also called hydrostatic pressure or water pressure, is the force exerted by the weight of water at a given depth in a body of water, such as the ocean, a lake, or a swimming pool.  It is a result of the gravitational pull on the water column above a specific point in the water.

Key Points about Underwater Pressure

  • Depth  -  The deeper you go underwater, the greater the pressure is because there is more water above you, and the weight of this water column exerts a greater force.
  • Gravitational Force  -  The strength of the Earth's gravitational pull affects underwater pressure.  The higher the gravity, the greater the pressure at a given depth.
  • Density of the Fluid  -  The density of the water also plays a role.  Saltwater, for example, is denser than freshwater, so it exerts slightly higher pressure at the same depth.

As you descend deeper underwater, the pressure increases linearly with depth.  For every 10 meters (33 feet) you descend in seawater, you experience an increase in pressure of approximately 1 atmosphere (atm).  At the surface, the pressure is approximately 1 atm (101.3 kPa), but at a depth of 10 meters, it is roughly 2 atm, and at 20 meters, it is approximately 3 atm, and so on.

Understanding underwater pressure is essential for various applications, including scuba diving, submarine operations, and the design of underwater structures.  Divers need to be aware of pressure changes to avoid conditions like decompression sickness, which can result from rapid changes in pressure during ascent.  Submarines and underwater vehicles also need to account for pressure changes to ensure their structural integrity.


 Underwater Pressure formula

\( p_u = \rho \; g\; d  \)     (Underwater Pressure)

\( \rho =  p_u \;/\; g\; d \)

\( g =  p_u \;/\; \rho \; d \)

\( d =  p_u \;/\; \rho \; g \)

Symbol English Metric
\( p_u \) = underwater pressure \(lbf\;/\;in^2\)   \(Pa\)  
\( \rho \)   (Greek symbol rho) = density of water \(lbm\;/\;ft^3\) \(kg\;/\;m^3\)
\( g \) = gravitational acceleration \(ft\;/\;sec^2\)   \(m\;/\;s^2\)  
\( d \) = depth under water \(ft\)  \(m\) 


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Tags: Pressure Water