Many people consider air to be weightless, an invisible and insubstantial part of our environment. However, air does possess weight. The Earth’s atmosphere, a vast ocean of gases, exerts a measurable force due to its mass. Understanding this property of air reveals its profound influence on our planet and daily lives.
Demonstrating Air’s Weight
A deflated basketball placed on a sensitive scale will show a slight weight increase when inflated with air. This demonstrates that the added air contributes to the overall mass. Similarly, a balanced stick with two deflated balloons at each end can illustrate this concept. Inflating one balloon will cause that side of the stick to dip, indicating the inflated balloon is heavier due to the air inside it.
The Science Behind Air’s Weight
Air possesses weight because it is composed of molecules, primarily nitrogen and oxygen, which, like all matter, have mass. Earth’s gravity pulls on these individual air molecules. This pull of gravity on the immense number of molecules in the atmosphere gives air its collective weight. The concept of density, defined as mass per unit volume, directly relates to air’s weight. Denser air contains more molecules packed into a given space, resulting in a greater weight for that volume.
Quantifying Air’s Weight
The weight of air is quantified through atmospheric pressure, the force exerted by the column of air above a surface. At sea level, the standard atmospheric pressure is approximately 14.7 pounds per square inch (psi), or 101.3 kilopascals (kPa). This means that every square inch of surface at sea level has about 14.7 pounds of air pressing down on it. Barometers measure this pressure. Classic mercury barometers balance the weight of a mercury column against the atmospheric pressure, while aneroid barometers use a flexible metal box that expands or contracts with changes in air pressure.
How Air’s Weight Affects Us
The weight of air significantly impacts our world, influencing weather and human physiology. Changes in atmospheric pressure drive weather patterns; low-pressure systems are often associated with cloudy skies and precipitation, while high-pressure systems typically bring clear weather. Atmospheric pressure also enables actions like drinking with a straw. When you suck on a straw, you reduce the air pressure inside it, allowing the higher atmospheric pressure outside to push the liquid up. For individuals at high altitudes, reduced atmospheric pressure means fewer oxygen molecules per breath, making it harder for the lungs to absorb enough oxygen, which can lead to altitude sickness.