Atmospheric Pressure Demonstration
So how powerful is plain-old atmospheric pressure? Well, atmospheric pressure at sea level is approximately 14.7 pounds per square inch (or PSI) above the vacuum of outer space. This might not seem like a lot considering that most car tires are inflated to 30 or 40 PSI above this level (i.e., a total pressure of 44 to 54 PSI above a vacuum), and some bicycle tires are inflated up to 80 or 90 PSI (or 94 to 104 PSI above a vacuum).
This basic pressure of 14.7 PSI, caused by the sea of air above our heads, pushes on us every day of our lives and is the reason that the oceans are liquid and you're alive. It's not that much pressure, but enough to get the job done.
Looking at it another way, 14.7 PSI is (when we adjust the units) roughly 2,116 pounds per square foot (PSF). So, for each and every square foot of area on your body, you have a force of slightly over one ton, or the weight of a small car, pushing on it!!!
Maybe atmospheric pressure is a big deal after all... Maybe we can see it's effect in real time...
The video demonstration shown in this article is of a hot aluminum can with a very small amount of boiling water in it being placed into a beaker of cold water. Below is a photo of the test setup. Nothing elaborate is required for this experiment, just an empty aluminum can (a can of V8 in this case - we're trying to be somewhat health conscious here), a heat source (lab hotplate), a tank of water (in this case a one liter beaker filled with ice water), and a set of tongs to grab the VERY hot can.
The can, sitting as shown in the photo, has effectively equal atmospheric pressure inside and outside.
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| The Test Setup |
Take a look at the video demonstration below to see what happens when the atmosphere pushes in on the can. You are looking at the motion at 1/10th speed or 300 frames per second. Once the water is fully boiling within the can, we quickly grab it and place it into the water with the open end pointing downward (so no atmospheric air can rush in). At this point, the water vapor pressure inside the can decreases and a vacuum is created. The can is easily crushed and pulled into the water due to its loss of buoyancy. No excess force is applied with the lab tongs, we are just lightly holding the can in place, the atmospheric pressure does all the work.
Slow Motion Video of Atmospheric Pressure Crushing a Can
So, what's going on here???
Most of the air within the can is being expended through the boiling of the water inside it, and the full pressure of the atmosphere is squeezing the can (around 2,116 PSF) in all directions. Since this can has an exposed surface area of roughly 0.2 square-feet, the net crushing force is about 425 pounds, which is more than enough force to collapse the sides. As the can collapses, the vacuum pulls the can downward expelling any remaining pressure and pulling the cold water inside the can.
This is what an implosion looks like.
This demonstration need not be limited to a small aluminum can. There are many videos on the internet showing this experiment for large 55 gallon oil drums. The results are clearly much more spectacular.