Which best describes absolute pressure?

Absolute pressure is defined as the total pressure exerted on a substance, measured relative to a vacuum. It encompasses both the ambient atmospheric pressure and any additional pressure resulting from a fluid or gas above it.

In underwater contexts, as you descend, the pressure due to the water column adds to the existing atmospheric pressure. At sea level, atmospheric pressure is approximately 101.3 kPa (kilopascals), and as you dive deeper, the pressure increases due to the weight of the water above. Therefore, absolute pressure gives a complete picture of the actual pressure experienced at a particular depth, making it essential for understanding buoyancy, decompression, and other physics principles relevant to diving.

Other options describe pressures but do not fully represent absolute pressure. The one that highlights only the pressure exerted by a fluid minus atmospheric pressure refers to gauge pressure. The option referring solely to atmospheric pressure overlooks the significant additional pressure from the fluid column. Finally, the pressure of water above sea level does not relate to the concept of absolute pressure as it fails to account for the sum of atmospheric pressure and other pressures at depth.