What is the term for pressure that is lower than atmospheric pressure?

What is the term for pressure that is lower than atmospheric pressure?

• A. Vacuum
• B. Residual Pressure
• C. Static Pressure
• D. Gauge Pressure

Answer: (A)

Vacuum is the term for when the pressure in a space is less than the surrounding atmospheric pressure. The atmosphere at sea level is about 14.7 psi, so any absolute pressure below that is considered a vacuum. If a gauge shows a negative reading, that indicates a vacuum condition relative to atmosphere, which is another way to describe sub-atmospheric pressure. The other terms don’t capture this specific idea: residual pressure means leftover pressure after a process; static pressure is the actual pressure at a point in a fluid at rest; gauge pressure is the pressure measured relative to atmospheric and can be negative or positive, but the label for sub-atmospheric pressure is vacuum.

Vacuum is the term for when the pressure in a space is less than the surrounding atmospheric pressure. The atmosphere at sea level is about 14.7 psi, so any absolute pressure below that is considered a vacuum. If a gauge shows a negative reading, that indicates a vacuum condition relative to atmosphere, which is another way to describe sub-atmospheric pressure. The other terms don’t capture this specific idea: residual pressure means leftover pressure after a process; static pressure is the actual pressure at a point in a fluid at rest; gauge pressure is the pressure measured relative to atmospheric and can be negative or positive, but the label for sub-atmospheric pressure is vacuum.