When you push up the balloon in a lung model, the space inside the bottle gets smaller , so the air pressure increases and the lung balloon deflates as air is pushed out. In the real body, this is like exhaling : the diaphragm relaxes, chest volume decreases, and air leaves the lungs.

What’s happening

  • Smaller volume = higher pressure.
  • Higher pressure pushes air out of the lung balloon.
  • The balloon gets smaller or collapses until the pressure inside and outside balance again.

Quick scoop

If you pull the bottom balloon down , the lung balloon inflates; if you push it up , the lung balloon deflates.

If you want, I can also explain it in one sentence for a worksheet answer.