6. Gauge pressure and absoute pressure

We perform all our daily activities under the atmospheric pressure. We are so used to it so that we do not even realize it. When blood pressure and tyre pressure are measured using instruments, they show the pressure over the atmospheric pressure. Hence, absolute pressure is zero-referenced against a perfect vacuum, and gauge pressure is zero referenced against atmospheric pressure.

  

For pressures higher than atmospheric pressure,
Absolute pressure \(=\) Atmospheric pressure \(+\) Gauge pressure

For pressures lower than atmospheric pressure,
Absolute pressure \(=\) Atmospheric pressure \(–\) Gauge pressure

 

We have seen that the liquid column exerts pressure, so the pressure inside the sea will be more (which is more than twice the atmospheric pressure). Parts of our body, especially blood vessels and soft tissues, cannot withstand such high pressure. Therefore, scuba divers always wear special suits and equipment to protect themselves.