Windbag - The Bernoulli Bag
How many breaths does it take to fill a 2 meter long bag?
Here's the challenge... How many breaths would it take to blow up a 2 meter (8 ft) long bag? Depending on the size of the person, it may take anywhere from 10 to 50 breaths of air. However, with a little practice... and some scientific knowledge of air... you will be able to inflate the bag using only one breath!
Steve demonstrated the Windbags and the power of air at the 9News Weather and Science Day at Coors Field in Denver, CO. Read more about the 9News and Steve Spangler Weather and Science Day.
- The "Windbag" is actually a long plastic bag in the shape of a tube. While you can purchase these bags from toy stores that sell science experiments, you can also make your own long bag using a product called a Diaper Genie refill. It's part of a diaper system that parents use to dispose of diapers. A Diaper Genie refill is commonly available at any major discount/department store.
- You can also check out our colorful Windbags and purchase them in various quantities
- Tie a knot in one end of the bag. Invite a friend to blow up the bag, keeping track of the number of breaths it takes. Then, let all of the air out of the bag. Explain to your friend that you can blow up the bag in one breath... chances are they won't believe you, but that's all part of the fun!
- Have your friend assist you by holding onto the closed end of the bag. Hold the open end of the bag approximately 10 inches away from your mouth. Using only one breath, blow as hard as you can into the bag. Remember to stay about 10 inches away from the bag when you blow.
- Quickly seal the bag with your hand so that none of the air escapes. Tie a slip knot in the end of the bag, or let the air out and try again.
How does it work?
The long bag quickly inflates because air from the atmosphere is drawn into the bag from the sides along with the stream of air from your lungs.
For you science enthusiasts out there - here's the technical explanation... In 1738, Daniel Bernoulli observed that a fast moving stream of air is surrounded by an area of low atmospheric pressure. In fact, the faster the stream of air moves, the more the air pressure drops around the moving air. When you blow into the bag, higher pressure air in the atmosphere forces its way into the area of low pressure created by the stream of air from your lungs. In other words, air in the atmosphere is drawn into the long bag at the same time that you are blowing into the bag.
Additional InfoFirefighters use Bernoulli's principle to quickly and efficiently force smoke out of a building. Instead of placing the fans up against the doorway or window, a small space is left between the opening and the fan in order to force a greater amount of air into the building. Firefighters call this "Positive Air Flow."
Marie Cote - December 2, 2012
This was such a fun way to get my students WONDERING and THINKING....I could just see the wheels turning while they watched their friends (and their teacher) try to blow up our windbags. I would recommend this to ANYONE!