Lots of science toy companies will sell you this experiment, but why not make your own? You’ll need to find a loooooong bag, which is why we recommend a diaper genie. A diaper genie is a 25′ long plastic bag, only both ends are open so it’s more like a tube. You can get three 8-foot bags out of one pack.
Kids have a tendency to shove the bag right up to their face and blow, cutting off the air flow from the surrounding air into the bag. When they figure out this experiment and perform it correctly, this is one of those oooh-ahhh experiments that will leave your kids with eyes as big as dinner plates.
Here’s what you do:
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Cut an eight-foot section of the diaper genie bag and knot one of the ends. Hold the other end open, take a deep breath, and blow. How many breaths does it take for you to fill up the entire bag with air? Try this now…
After you know how many breaths it takes, do you think you can fill the bag with only ONE breath? The answer is YES! Hold the bag about eight inches from the face and blow long and steady into the bag. As soon as you run out of air, close the end of the bag and slide your hand along the length (toward the knotted end) until you have an inflated blimp.
Troubleshooting: If the bag tears open, use packing tape to mend it.
What’s going on? When you blow air past your lips, a pocket of lower air pressure forms in front of your face. The stronger you blow, the lower the air pressure pocket. The air surrounding this lower pressure region is now at a higher pressure than the surrounding air, which causes things to shift and move. When you blow into the bag (keeping the bag a few inches from your face), you build a lower pressure area at the mouth of the bag, and the surrounding air rushes forward and into the bag.
Substitution Tip: If you can’t locate a diaper genie, you can string together plastic sheets from garbage bags, using lightweight tape to secure the seams. You’ll need to make a 8-12” diameter by eight-foot long tube and close one end. When kids get their eight-foot bag inflated in just one breath, ask them: “Did you really have that much air in your lungs?”