How could this railroad tanker car be crushed so easily? Watch the video below and see if you can figure it out. You will find an explanation to this dramatic demonstration below!
So what caused this steel railroad tanker car to be crushed like a flimsy, aluminium pop can? The answer is air pressure. There was enough of a difference in air pressure between the air pressure inside the tanker and the air pressure of the air surrounding the tanker that the steel in the tanker gave out. But what is air pressure? How was the difference in air pressure established? Why does the difference in air pressure cause the tanker to implode?
Imagine you were standing in a park minding your own business and somebody whipped a baseball at your head. Obviously, you would feel this collision and it would probably even hurt quite a bit. Now if you could imagine being repeatedly pelted with thousands of baseballs from every direction and from all angles. Not only would this hurt an a lot it would also probably make it very difficult to move from the spot you were standing. As you are sitting there reading this post, you experiencing something quite similar to the example with the baseballs. Right now there are billion and billions of collision every second between you and the molecules in the air. You cannot feel these collision, however, this is air pressure. Air Pressure is the force exerted by air, by these billions of collisions, with any surface the air is in contact with.
There is also an immense amount of weight pressing down on you from all of the air above you. If we measured all of the air starting with the air that is resting on your shoulders up to the top of the atmosphere, we will find that you have around 1000 kg of air pressing down on your body! This is the same mass as a small car! We don’t notice this incredible pressure on our bodies because our bodies are meant to function in this pressure.
Now lets understand how the difference in air pressure between the contents of the tanker and the surroundings was established. You may have noticed the large hose that was connected to the tanker car. This hose is actually a part of a vacuum pump which was gradually pulling air out of the huge tanker. It isn’t evident from the video how long this vacuum pump was working, but I imagine it must have taken quite some time to pump out enough air from the tanker.
Finally, how was this steel tanker crushed so easily? We now understand of how immense the pressure of the atmosphere is at sea level. This air pressure has always had enough force to crush this tanker however, since the tanker has had the same amount of air pressure inside as it does on the outside, the tanker was not crushed. This is kind of like if you were in a tug-o-war against yourself, no one wins! Now if “yourself” let go of the rope you would most likely go flying backwards, thus winning the tug-o-war. Taking all of the air out of the tanker is just like letting go of the rope. The air pressure on the outside was finally able to outmatch the air pressure on the inside.