At my school we’ve been learning about air pressure and on our homework sheet it says a boy named John and his friends hiked up to a forest fire lookout station at an elevation of 2445m. at the top of the moutain John drank the rest of his water put the cap on and put the bottle in his backpack 3 days later when he was at home in seattle he was going threw his backpack and looking at what was in his backpack and found that his bottle was now in the shape of an hour glass. When John took the cap of he heard a hissing sound and the bottle slowly returned back to its normal shape. What happened to John’s bottle and why did the squashed bottle make a hissing noise? Thank You for all your help!!!