What is absolute pressure in a system?

Study for the Massachusetts 3rd Class Engineer Exam. Access flashcards and multiple choice questions with hints and explanations. Prepare for success on your exam!

Absolute pressure is defined as the total pressure exerted on a system, which includes both the gauge pressure and the atmospheric pressure. It is a measure of the actual pressure in a system relative to a perfect vacuum.

When considering the choices, the first option stating that absolute pressure is the pressure when the gauge reads zero is not accurate; if a gauge reads zero, it indicates that the pressure is equivalent to the atmospheric pressure, not that it is the absolute pressure. In contrast, the correct concept of absolute pressure is encapsulated in the last choice, which describes it as the total pressure including atmospheric pressure. This understanding is vital in many engineering applications, such as calculating performance in systems involving fluids, where it is necessary to know the absolute pressure to ensure measurement accuracy.

The second choice, mentioning the pressure exerted by air at standard conditions, refers to a specific context of atmospheric pressure but does not define absolute pressure adequately. The third option, which describes pressure above atmospheric pressure only, outlines gauge pressure, not absolute pressure, as it measures pressure relative to atmospheric conditions alone.

Overall, the key to understanding absolute pressure lies in recognizing that it accounts for the total pressure in the system, incorporating atmospheric influence into the calculation.

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