Air pressure

Air is made up of different tiny molecules. These molecules constantly collide with surfaces. The surface of your skin sustains billions of collisions every second. The molecules are so small that we hardly feel the impacts. Take a glass window for example, the number of collisions on the outside of the window equal the number of collisions on the inside. This balance prevents the glass from being smashed by the air pressure. Conduct the following demonstration where the number of collisions on the outside of the can far exceed those on the inside.
The air pressure has crushed this can. Click to see a 120kb movie .
Click to see a 120Kb video of the imploding can.

A large coffee tin. The can has a hole placed at the base of the can. A small amount of water 10cm is placed inside and the top placed on firmly.

As the water is heated in the can, steam displaces all the air inside. Water molecules now totally take over the interior of the can. Explain what happens to crush the can when it is placed in the water. Use the words molecules, collisions, condensation, vacuum, air pressure.
Continue with the Magic Water Bottle.
Continue with the Giant Marshmallow
Continue with air pressure and Bernoulli's Law.