Explore Bernoulli’s principle of air pressure with this long plastic bag. If you place it firmly to your mouth (like a balloon), it will take many breaths to blow it up. But if you hold it out in front of your mouth and blow, air pressure in the stream you produce is reduced, entrapping surrounding air to join in, filling up the bag. You can blow it up with a single breath! This is especially effective after your students have counted many of their own breaths in attempts to fill up the bag! Sold in packs of 4. Comes with a Teacher's Guide.