Fill the 1-liter plastic bottle with very warm water.
Then, empty the water out of the bottle.
Now twist the cap back on the bottle, tight.
Put the bottle in the ice water. What happens? The bottle collapses.
Here's the reason why the bottle collapses: When you pour very warm water into the bottle, there are two things in the bottle: water and air. The very warm water warms the air inside the bottle. After you pour the warm water out, all that's left in the bottle is the warmed air.
When you put the bottle in the ice water, the air inside the bottle gets colder, takes up less space, and doesn't push as hard against the inside walls of the bottle.
But, there's also air outside the bottle. That air pushes harder on the outside of the bottle than the air pushing on the inside of the bottle. So, the air on the outside of the bottle smooshes the bottle.
To test out this explanation try the same thing you did before, except instead of putting the bottle in ice water, put it into a bowl of warm water. What happens?