Bennett Mechanical Comprehension Practice Test 2026 – The Complete All-in-One Guide to Exam Success!

The equation P = ρ · g · h is derived from the principles of hydrostatics, which assumes a uniform density of a fluid in a gravitational field. When applying this equation to air pressure, it is important to recognize that the density of the atmosphere is not uniform; it changes with altitude due to variations in temperature, pressure, and the composition of air.

At sea level, air is denser, and as one ascends to higher altitudes, the density decreases. This variability in density means that applying a simple static fluid equation can lead to inaccuracies. In practice, air behaves more like a compressible fluid, and its pressure decreases exponentially with height rather than linearly as suggested by the equation if density were considered constant.

Understanding the non-uniform nature of density in the atmosphere is crucial for accurately calculating air pressure at different heights, and it highlights the complexities of atmospheric physics that go beyond the assumptions made for simple fluids.