Final Answer:
The pressure experienced by the scientist at a depth of 9 feet below the surface in salt water is 18.7 pounds per square inch.
Step-by-step explanation:
When a scientist submerges into salt water, the pressure acting on them is the sum of atmospheric pressure and the pressure due to the water column above. At a depth of 9 feet, the pressure due to the water column is significant, contributing to the total pressure. This pressure is quantified as 18.7 pounds per square inch.
To comprehend this, it's essential to recognize that water exerts pressure with depth. The pressure due to the atmosphere remains constant, but as the scientist descends, the weight of the water column above them increases, leading to elevated pressure. This phenomenon is described by Pascal's Law, stating that a change in pressure at any point in an enclosed fluid is transmitted undiminished throughout the fluid.
In the case of the scientist at 9 feet, the pressure increase is a result of the water pressing down from above. This has practical implications, especially in underwater activities and engineering, where understanding pressure changes is crucial for safety and design considerations.