Which term describes pressure in relation to atmospheric pressure?

• A. Absolute pressure
• B. Static pressure
• C. Relative pressure
• D. Impact pressure

Answer: (C)

Pressure relative to the surrounding air is called relative pressure, also known as gauge pressure. This is the amount of pressure above (or below) the local atmospheric pressure, so it uses the atmosphere as the zero reference. The reason this is the best answer is that gauge pressure tells you how much pressure a system has compared to the ambient air around it, which is exactly what “in relation to atmospheric pressure” means.

Absolute pressure, by contrast, uses a vacuum as zero, so it’s the total pressure plus the atmospheric baseline. Static pressure refers to the actual ambient air pressure at a point (the local atmospheric pressure), and impact pressure is the dynamic portion—the difference between total pressure and static pressure.