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The atmospheric pressure is 101325 Pa,which is good enough to get our bones crushed.But why aren't we crushed due to it?

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  • $\begingroup$ Once I saw a cartoon where the main character thought that taking the air out of a sphere would make it float. The sphere collapsed. $\endgroup$
    – PML
    Apr 9 '14 at 10:10
  • $\begingroup$ Because the atmosphere also pressurize the body. Diving down 100 meters will pressurize the gasses in the body and they will compress, like the air in our lungs and if the lung volume get below half a litre the lungs can get partly filled with blood plasma. But sorry no bone crushing. But if you take a big breath and hold it while you ascend from 100 meters to the surface, your ribs may start to break $\endgroup$
    – Enos Oye
    Apr 9 '14 at 11:58
  • $\begingroup$ Bird bones are air filled to save weight, and might break if they are pressurized far beyond 1 atmosphere. $\endgroup$
    – Enos Oye
    Apr 9 '14 at 12:02
  • $\begingroup$ Vacuum spheres are used on many underwater vessels for constant buoyancy. @PML $\endgroup$
    – Enos Oye
    Apr 9 '14 at 12:04
  • $\begingroup$ @EnosOye It was a cartoon plus the sphere was made of a very weak material. =p $\endgroup$
    – PML
    Apr 9 '14 at 13:43
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The reason is quite simple: the contents of our bodies (blood, bones, muscle, etc) are at the same pressure as the atmosphere.

Even if they were not, atmospheric pressure is certainly not enough to get our bones crushed. When a diver is 10m under water, the pressure is doubled (202650 Pa). Any recreational diver can do that. I have been deeper than that, without any ill effects. At 100m, the pressure is 10 times atmospheric pressure, and only specially trained divers, with special equipment (including breathing gas that has nitrogen reduced and replaced by some other gas like helium) can go there. The deepest verified dive is 318m - about 32x atmospheric pressure.

Fish and other marine creatures have their internal body pressure the same as the water around them. As a result, even in the deepest oceanic trenches there is life.

The reverse is more dangerous. If our body was exposed to vacuum, the internal pressure would quickly kill us, as explained in this question.

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There are five good answers in this link:

Answer 5:

It's true that the weight of the column of air above us is very heavy. We can call this weight an external pressure, because it is pushing down on us. However, the reason we, nor other objects, are crushed by the weight of this air is because this external pressure is balanced by our internal pressure, which arises from various fluids and materials we are composed of. This internal pressure exists because we are largely made up of incompressible solids and liquids. To simplify matters, just think about a balloon filled with water. The external pressure is trying to compress the balloon, while the water inside the balloon is able to balance this external pressure due to the relative incompressibility of water. This incompressibility is responsible for the internal pressure opposing the external pressure.

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