Air pressure, or atmospheric pressure, is the force exerted on objects by the atmosphere. Barometers are typically used to measure atmospheric pressure. Made of a liquid filled glass tube, the level of liquid will rise when the pressure increases and fall when the pressure drops. Lower barometric pressure tends to be associated with precipitation and cloudiness, while higher readings are related to sunshine and calmer weather. Air is made of invisible particles. The density of these particles is affected by atmospheric pressure. The greater the pressure, the more densely packed the particles are. In comparison, less pressure means a lower density of air particles. While the particles are too small to be observed, the effects of the particles and changing their density are often visible.
Everything is made of matter, which is composed of atoms. Atoms are too small to be seen with the human eye. Matter has volume and mass. Mass refers to the amount of matter in an object. Volume will be affected by pressure changes, whereas mass will not
