Here is another example of air pressure. First water is added to the aluminum can. The water in the can is then boiled. When steam comes out of the can all the air in the can has been replaced with hot steam. You could not survive in the can if you were inside it because not only is it very hot but there is no air! It is all steam! The pressure of the steam in the can is the same as atmospheric pressure outside of the can. The pressures are balanced inside and outside the can. When the can is inverted and placed into the ice water the steam inside can condenses turning into a very thin film of water along the insides of the can. There is very little gas inside the can! In other words a vacuum is created inside the can. Vacuums have do not have pressure because they do not have gas! With no pressure inside the can, atmospheric pressure crushes the can from all directions with a weight of 14.7lbs over every square inch.

Here it is again in slow motion.

Let’s try something else.

In a plastic bottle let’s put a balloon and try blowing it up. It is impossible because air pressure builds up inside bottle when the balloon tries to expand...the air inside the bottle can not escape. So let’s use a tack and puncture the bottom of the bottle. now air can escape and we can blow up balloon. When we stop blowing and don’t block the hole air reenters the bottle while the balloon returns to being unstretched. This time lets blow up the balloon then block the hole with a finger. The balloon retains its shape because the pressure inside the balloon is atmospheric pressure and the pressure outside the balloon is less than atmospheric due to the closed hole! Air wants to rush in to the lower pressure traveling through the hole into the bottle but it is being blocked by the finger.

when remove the finger air rushes to equilibrate the pressure on both sides of the balloon. now the balloon is just like any other deflated balloon!


Let’s try again blowing up the balloon, blocking the hole with tape, then filling the balloon with water! Look what happens when the tape is removed!

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