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The air in a column above a 15 cm × 15 cm patch on a person's head exerts a downward force of about 2250 N (equivalent to the weight of a 225 kg mass). However, the head is not crushed under this enormous force. Which statement BEST explains why?
AThe skull is strong enough to permanently withstand 2250 N of force.
BThe pressure inside the body (in blood and tissues) is also equal to atmospheric pressure, so the pressures balance from inside and outside.
CGravity does not act on the air column above the head.
DAir is too light to exert any real pressure on solids.
Answer & Solution
Correct answer: B. The pressure inside the body (in blood and tissues) is also equal to atmospheric pressure, so the pressures balance from inside and outside.
The atmospheric pressure pushes inward on every part of the body. Our internal fluids — blood, tissue fluid, air in lungs — are themselves at roughly the same pressure, so they push outward with the same force. The two opposing pressures balance, and we feel no net inward force. Option A is wrong because air does exert measurable pressure. Option B is misleading: even a strong skull would deform under a continuously applied 2250 N — what saves us is the balance, not raw strength. Option D contradicts the very reason atmospheric pressure exists.
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