Humans evolved in Earth's atmosphere, therefore the pressures interior to the body are relatively close to atmospheric pressure. Because the differences between internal body pressures and atmospheric pressure are so small, individuals have a difficult time gauging the magnitude of atmospheric pressure. Suppose an individual is lying on his stomach with sheets of paper stacked on his back. If each sheet of paper has a mass of 0.00320 kg and is the standard letter size of 8.5 in by 11 in ( 0.216 m by 0.279 m ), how many sheets must be stacked to produce a pressure on his back equal to atmospheric pressure (roughly 101325 Pa )?

193664 sheets of paper.

Explanation:

We know that the pressure is defined as

In words, the applied force divided by the area of application. The area of a single sheet of paper is

The force exerted by a single sheet of paper is its weight, given by teh expression:

(Where m is the mass of a single sheet and g is the acceleration due to gravity on earth)

And, for sheets of paper, the total weight is:

Now, substituting this in the definition of pressure and solving for , we get:

Finally, plugging in the known values, we can compute :

This means that there must be 193664 sheets stacked to produce a pressure equal to atmospheric pressure.

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