Absolute pressure is defined as the sum of atmospheric pressure and system pressure starting from what reference point?

Absolute pressure is defined as the sum of atmospheric pressure and system pressure starting from what reference point?

• A. A theoretical vacuum
• B. A complete vacuum
• C. Atmospheric pressure
• D. Outside air pressure

Answer: (A)

Absolute pressure is measured from a zero reference point that is a theoretical vacuum—no pressure at all. Because of that, the absolute value represents how much pressure exists above that zero-point. In practical terms, you take the pressure you measure in the system relative to the surrounding air (the gauge pressure) and add the atmospheric pressure to it. The result is the pressure on the absolute scale, since the zero is the theoretical vacuum. A complete vacuum isn’t physically achievable, which is why we use the term theoretical vacuum as the reference. Describing pressure relative to outside air would give gauge pressure, not absolute.

Absolute pressure is measured from a zero reference point that is a theoretical vacuum—no pressure at all. Because of that, the absolute value represents how much pressure exists above that zero-point. In practical terms, you take the pressure you measure in the system relative to the surrounding air (the gauge pressure) and add the atmospheric pressure to it. The result is the pressure on the absolute scale, since the zero is the theoretical vacuum. A complete vacuum isn’t physically achievable, which is why we use the term theoretical vacuum as the reference. Describing pressure relative to outside air would give gauge pressure, not absolute.