Dr. Christopher S. Baird

# Why don't I feel the miles of air above me that are crushing me down?

Category: Physics      Published: September 14, 2015

By: Christopher S. Baird, author of The Top 50 Science Questions with Surprising Answers and Associate Professor of Physics at West Texas A&M University

Because air is a fluid, the weight of the air is transmitted to the palm of your hand and to the back of your hand at the same time. These forces cancel so that your hand overall feels no net force. Public Domain Image, source: Christopher S. Baird.

Air does not crush you down. As a fluid, air flows around you and tries to crush you in. Fortunately, there is typically just as much pressure inside your body pressing outward as there is air pressure outside your body pushing inward. They typically cancel out, meaning that there is no overall force on you and you don't get crushed. Even when the internal and external pressure don't exactly cancel each other out, your skin, muscles, and other tissues are usually strong enough and flexible enough to not be damaged by the force.

Stand outside in a field and look straight up. You are looking at a one-hundred kilometer column of air that is being pulled down toward you by gravity. Although air is very tenuous compared to other materials, it is indeed composed of atoms and indeed has mass. As such, air is pulled down by gravity just like everything else that has mass. A handful of air may not have much mass, but one hundred kilometers of air is a different story. If you draw a one-meter by one-meter square on the ground (which is about the footprint of fridge), then all of the air directly over that square has a total mass of about ten thousand kilograms. Because of earth's gravity, this mass pushes down on the square meter with a force of about twenty thousand pounds, which is the same as the weight of an empty school bus. In other words, if you placed an empty school bus on a square meter pedestal (to focus the force to the right area), the patch of ground under the pedestal would be experiencing just as much weight from the bus as it normally does from air.