What you need:
• a bottle of water
• a needle
What you do:
• Put six small holes near the bottom of the bottle, all around it.
• Give the bottle to your friend and ask him to have a drink.
• Watch what happens.
When the cap is on the bottle, the air pressure in the bottle is equal to the air pressure outside the bottle. Since the pressure is the same nothing comes out of the uncovered hole at first. When the cap is taken off, the water squirts out of the bottle. The water pressure in the bottle is greater than the air pressure on the out side of the bottle. The reason for this is because the weight of the water caused by gravity has a greater pressure then the air pressure outside of the bottle.
The weight of the water in the bottle causing pressure causes the water to shoot out of the lowest hole the farthest. This is because the height of more water above the hole has more weight and creates a greater pressure that the hole that is higher on the bottle.