Air pressure
Air pressure is the weight of air molecules pressing down on the Earth. The air pressure is highest at the sea level.
Experiment-1
Water which doesn't spill out of upside down glass. This is because of the air pushing the card upside which is greater than the gravity (weight of the water) which is pulling the water down..
Experiment -2
Crushing the water bottle.
In this experiment when we pour hot water it heats the air inside the bottle which expands and becomes lighter and moves out of the bottle when we close the mouth of the bottle and pour the cold water on it the little bit air inside the bottle cools and contracts creating low pressure, since the bottle is not strong enough to withstand the high pressure of the surrounding air so it gets crushed.
Experiment 3
Thirsty bottle
When we pour hot water in the bottle it heats the air inside the bottle which expands and becomes lighter and moves out of the bottle creating low pressure. As the air cools and contracts vacuum is created (low pressure area) when we bring the bottle near the water quickly the atmospheric pressure forces the water into the bottle..
