Fluids push rather than pull, so in most cases absolute pressure cannot fall below zero. What is the smallest gauge pressure that can therefore occur?
AZero, since gauges read zero in air
BOne atmosphere below absolute zero
CMinus one atmospheric pressure
DThere is no lower limit at all
Answer & Solution
Correct answer: C. Minus one atmospheric pressure
1. Absolute pressure equals gauge pressure plus atmospheric pressure.
2. Fluids push rather than pull, so in most cases the smallest absolute pressure available is zero.
3. Setting the absolute pressure to zero gives gauge pressure = zero minus atmospheric pressure.
4. The smallest gauge pressure is therefore minus one atmospheric pressure, a negative reading.
5. Zero gauge pressure is the reading in ordinary air, which is the middle of the range rather than its bottom.
6. There is no theoretical ceiling on how large a gauge pressure can be, but that is a statement about the top of the range, not the bottom.
7. Absolute zero is a temperature, so an atmosphere below it is not a pressure statement at all.
_Source: OpenStax College Physics (CC BY 4.0), Ch 11 "Fluid Statics", section 11.6 Gauge Pressure, Absolute Pressure, and Pressure Measurement_
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