Final answer:
The greatest relative pressure change in seawater occurs between 0 and 33 feet due to the significant increase of one atmosphere of pressure, which becomes less significant in relative terms at greater depths.
Step-by-step explanation:
The greatest relative pressure change in seawater takes place between 0 and 33 feet. This is because the rate of change of pressure with depth is greatest at the surface and decreases as depth increases.
The pressure at any depth in a fluid is given by the equation P = ρgh, where ρ is the density of the fluid, g is the acceleration due to gravity, and h is the depth. At the surface, moving from 0 to 33 feet, we experience the first atmosphere of pressure (which is approximately 1.013 × 105 N/m² or 14.7 psi).
Below 33 feet, each additional 33 feet adds another atmosphere of pressure, but the relative increase is less because we are adding to a pressure that is already higher. Therefore, the change from 0 to 33 feet represents the greatest absolute and relative change in pressure.