Gather your materials!
Cut the necks off of two of the balloons.
Cut one straw in half. Then, attach one balloon to each straw half. Use tape to seal it off. These will be your “lungs.”
Take the other straw and make a 2" (5.08 cm) cut on one end so that it is split in half.
Flip the straw around and make two 2” cuts on the other end so that it is split into four.
Tape one “lung” on either side of the two-way split straw.
Cut off the bottom of the bottle.
Remove the bottle cap and make a hole in the cap large enough to fit a straw through it.
We made the hole using a pushpin and then widened it with scissors.
Place your “lungs” inside the bottle, so that the balloons hang towards the bottom. Then, poke the four-way split end of the straw through the hole in the cap. Screw the cap back onto the bottle.
You may need to shorten your straw based on the size of your bottle. If it’s too long, shorten the straw so that the lungs are about 2” from the bottom of the bottle. Then, make the four-way split again.
Tape each of the split ends to the cap.
Cut the neck off of the last balloon and stretch it over the bottom of the bottle.
Pull on the bottom balloon to see a simulation of how lungs work!
Air pressure is a measure of how strongly air presses on things. It depends on a few factors, but one of the most important is volume, or the amount of space the air has. If you’ve ever pressed on a balloon to try to make it smaller, you’ve probably noticed that it gets harder to press the smaller you make it. That's because air pressure increases when you shrink the volume (like when you squish a balloon). The squished air pushes back harder against you. The reverse is also true: air pressure decreases when you increase the volume.
Air always tries to balance out pressure, so it will move from areas of high pressure to areas of low pressure. Your body uses this fact to move air in and out when you breathe. To breathe in, you expand your chest. That increases the volume in your lungs, which lowers their air pressure. Air rushes in to balance out the pressure. Then to breathe out, you shrink your chest, raise the air pressure in your lungs, and let the air rush back out.