CORPUS CHRISTI, Texas — Windy days are common here in the Coastal Bend and a good example of how air moves from high to low pressure. But not only does a difference in air pressure cause wind but it can also cause enough power to crush a can.
To demonstrate this, I will take an empty soda can and put a tablespoon of water in it then heat it up. As the water in the can heats up, the liquid water evaporates and rises in steam out of the can, replacing air molecules that were in the can with water vapor.
Without air molecules inside the can, the air pressure inside the can is lower than the air pressure outside the can.
Air always moves from high pressure to low pressure and in this case, air wants to go from outside the can where there is higher air pressure to the inside of the can where there is lower air pressure.
Now that the can is filled with water vapor, I will take the can off the burner and turn if over and place the opening of the can in cold water. The cooling down of the can will cause any remaining water vapor in the can to condense out into a small amount of water.
Without air molecules or water vapor in the can, there is nothing to stop the force of the outside air from rushing into the can. Since the top of the can is covered in water, the outside air tries to get inside the can from the sides and crushes it.