Fill a container with cold water. Place the neck of a glass bottle and a coin large enough to fit over the mouth of the bottle in the water for several minutes. Set the coin on top of the mouth and wrap your hands around the bottle. Within a few seconds, the coin should jump off. This is because the body heat in your hands caused the air inside to expand, increasing the pressure inside. This expanded air pushes upward on the coin, making it jump.
Remove the shell from a hard-boiled egg. Find a bottle with a neck thin enough that the egg can stand on it without falling in, but thick enough that it can squeeze through without breaking apart. Light a match and place it inside the bottle. Quickly place the egg on the mouth of the bottle with the small end down. The egg should be sucked into the bottle. This is because the fire of the match eats up the oxygen in the bottle, causing the pressure inside to be lower than the pressure outside, forcing the egg down.
Find an empty soda can and fill it halfway with water. Place the can on a heating plate or the burner of a stove until it steam comes out the top. Using a long pair of tongs, remove the can from the heat and place it top down in a tray of ice water. The can should crumple up within seconds. This is because steam from the water pushed out the air that was in the can, and when it was placed in ice water, the steam quickly turned back into water. Because the air was forced out, the pressure inside the can was lower than the outside pressure, and the can was crushed.
Fill a glass with water and let some spill over the edges so the rim gets wet. Remove the glass from the water and place an index card on top. Press down gently so that a seal will form. Turn the glass upside-down and the water will remain inside. This is because the pressure of the water on the card created by gravity does not have enough force to overcome the pressure of the air outside. Although you may think of air as empty space, it exerts 15 pounds of force on everything around you, including your body.