Explode/Implode and Sea Saws

The first photo is with no water and cold.

The second is with hot water and lid on.

And the third is with no water, lid on and cooled.

1. Inside and outside forces acting on the bottle are equal. => Normal shape
2. Hot forces acting on the inside are greater than the outside. => Bottle bulges
3. Hot water erupted. Lid on. Cool under cold water. Force acting on outside of bottle is greater than force acting inside.

Why?

Air pressure (a force) is greater. Air particles have more energy of push, or are "harder"against the bottle.

1. If two people were on a sea saw and are o equal weight where  do they need to sit on the saw to balance it? One on each end.
2. If 1 person is heavier, the heavier person needs to sit closer to the middle, and the lighter person on one end.

Note: Each person's weight is a force pushing down on the see saw.