Which of the following best describes gage pressure?

Gage pressure is defined as the pressure relative to atmospheric pressure. This means it measures the pressure of a fluid or gas in a system compared to the ambient atmospheric pressure surrounding that system. When a pressure gauge shows a value, it indicates how much pressure exceeds the atmospheric pressure rather than the total pressure, which includes atmospheric pressure.

For example, if a gage pressure reading is 30 psi, this means the pressure is 30 psi above atmospheric pressure. This definition is crucial in many applications, such as in water distribution systems, where understanding the pressure relative to the atmosphere can help in effectively managing water flow and ensuring the system operates safely and efficiently.

On the other hand, absolute pressure includes atmospheric pressure in its measurement, thus distinguishing it from gage pressure. Theoretical pressure under ideal conditions pertains to a conceptual scenario often used in engineering calculations but does not accurately reflect practical measurements such as gage pressure. Likewise, the boiling point of water is influenced by pressure, but it is not a direct measure of pressure itself, thus making that option irrelevant in the context of gage pressure.