Which instrument measures atmospheric pressure?

• A. Barometer
• B. Thermometer
• C. Anemometer
• D. Rain gauge

Answer: (A)

Measuring atmospheric pressure means figuring out how strongly air pushes on surfaces at Earth’s surface. The instrument that does this is a barometer. A barometer can use a column of mercury or a sealed flexible chamber to detect pressure changes: when air pressure rises, the mercury is pushed higher or the chamber compresses differently; when pressure falls, it drops. These pressure changes help scientists predict weather, because shifts in air pressure often accompany storms or clear skies. The other tools measure different things—thermometers check temperature, anemometers measure wind speed, and rain gauges track how much rain falls—so they aren’t used to measure atmospheric pressure.