Reply to ASK-AN-EARTH-SCIENTIST

Would a person weigh more in a denser atmosphere than in a less dense atmosphere? Does the pressure exerted by a column of air cause changes in a person's weight?

Actually, a person would weigh less in a denser atmosphere. "Weight" is how much you push down on a scale - which is different from "mass" which is how much matter you contain (which wouldn't change). The formula is: weight= mass*(gravitational acceleration). The pressure exerted by a column of air is the same in all directions, so a heavy atmosphere does not have weight since it pushes just as much up as it does down. What makes your weight be less in a heavy atmosphere is the buoyancy effect - your volume is taking up space that would normally be taken by the heavy air, and the mass of the displaced air is subtracted from your mass when calculating weight: your weight=(your mass-displaced air mass)*(acceleration of gravity). Note that if the mass of displaced air is equal to your mass, you will weigh nothing (neutral buoyancy), and if you weigh less than the displaced air (as you do in water) you will float.

Dr. Fred Duennebier, Professor

Department of Geology and Geophysics

University of Hawaii, Honolulu, HI 96822