If I were to fill a water bottle full of air and go up in elevation, would the water bottle expand or shrink? If I were to fill a water bottle full of air and go down in elevation, would the water bottle expand or shrink? I am at elevation 20000 I think.

a. Since the water bottle is filled with air at atmospheric pressure at 20000 ft, and since atmospheric pressure decreases with altitude, when we go up in elevation.

The pressure exerted by the molecules of air in the water bottle seek to balance out the atmospheric pressure as we go higher. Since the atmospheric pressure exerted by the molecules of air in the atmosphere are greater than that exerted by the molecules of air in the water bottle, this causes the volume of the water bottle to decrease and thus shrinks the water bottle until the pressure balances out

b. Since the water bottle is filled with air at atmospheric pressure at 20000 ft, and since atmospheric pressure increases with decreasing altitude, when we go down in elevation.

The pressure exerted by the molecules of air in the water bottle seek to balance out the atmospheric pressure as we go lower. The water bottle expands until the atmospheric pressure outside equals the pressure inside the water bottle.this causes the volume of the water bottle to increase and thus expands the water bottle until the pressure balances out