What principle does a barometer operate on?

A barometer operates on the principle that atmospheric pressure supports a liquid column. In a barometer, a tube filled with liquid (usually mercury or water, though mercury is more common due to its high density) is inverted into a reservoir of the same liquid. The atmospheric pressure exerted on the surface of the liquid in the reservoir pushes up on the liquid column in the tube. The height of this liquid column is directly related to the atmospheric pressure; as atmospheric pressure increases, the height of the liquid column rises, and as atmospheric pressure decreases, the height of the liquid column falls.

This principle effectively allows a barometer to measure changes in atmospheric pressure, which is crucial for weather forecasting and understanding environmental conditions. Understanding this mechanism highlights the fundamental relationship between pressure and the behavior of fluids in response to external forces.