Air moves out of the lungs when the pressure inside the lungs is greater than the pressure in the atmosphere.

Quick Scoop

When you breathe out (expiration), the volume of your lungs decreases, which makes the pressure of the air inside them rise slightly above atmospheric pressure. Because air always flows from a region of higher pressure to a region of lower pressure, it then moves out of the lungs into the surrounding air.

So, if this is from a multiple-choice question, the correct option is:

  • “Greater than the pressure in the atmosphere.”

In simple terms: squeeze the lungs a bit, pressure goes up, and air is pushed out toward the lower-pressure outside air.

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