Flying to San Antonio

In flight to San Antonio for the NSTA Science Teacher Conference. As promised I have a water bottle to show what happens to it during flight. I opened the bottle at sea level and as we ascended guess what happened to it. should it have contracted or expanded?

Hopefully you know that the bottle should have expanded due to the higher pressure on the ground and you should know that the air pressure decreases as you go up into Earth's Atmosphere. Since the bottle expanded, not much use it taking a picture of it since you really can't see it, but be sure to see a posted picture of it once we land later tonight. For now, I attached a picture of the stratus clouds in the distance. Check back later for more updates!