Windbag Experiment – Diaper Genie Balloons

Inflate an 8 foot long bag using a single breath of air thanks to help from Bernoulli

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How many breaths of air will it take you to fill a plastic bag that’s 8’ (2 m) long and 10” (25 cm) in diameter? Depending on your size, it may be anywhere from 10 to 50 breaths of air. Believe it or not, you can inflate a bag that holds 45 liters of air using only 1 breath. Seriously! Guaranteed to amaze your friends.

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Here's What You'll Need

  • Diaper Genie refill kit - or a Windbag
  • Scissors
  • Adult supervision

Let's Try It

  1. The “Windbag” is actually a long plastic bag in the shape of a tube. is your source to purchase the brightly colored Windbags pictured throughout the pages of this activity. But there is a real-world version of a long bag at your local department store. Head to the aisle where baby products are sold and look for a diaper disposal system (commonly referred to as a Diaper Genie). The long plastic bags are sold as refills to the diaper disposal system, and they work very well for this demonstration.

  2. If you’re using one of the Diaper Genie bags, cut off a section of the plastic tube material that is roughly 6 to 8 feet long. A shorter section of the bag (4 to 5 feet long) is recommended for younger kid-scientists.

  3. 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, squeeze 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 surprise.

  4. Put the bag over your mouth. Take your time, and blow three big breaths of air into it. Grab the bag in front of your mouth and squeeze your hand to close it off. Slide that hand forward down the bag pushing the air you blew into it toward the knotted end. How did you do? The bag is completely full. Right?

    Oh… not so much?

    How would you feel about inflating the entire bag with one breath?


  5. It may sound silly but, squeeze out all the air you just blew into the bag. 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. Make the opening as wide as you can with the index fingers and thumbs of both hands.

  6. Keep your mouth about 10 inches from the wide-open end of the bag. Using only one breath, blow a long, steady stream of air into the bag (just like you were blowing out candles on a birthday cake).

    You MUST keep your mouth off of the bag and keep the opening of the bag as large as possible. As you’ll soon see, the secret is actually in the open space between your mouth and the bag.

  7. If you do it correctly, you’ll see the bag quickly inflate. The trick is to quickly seal the bag with your hand so that none of the air escapes. Tie a slipnot in the end of the bag or let the air out and try again.

How Does It Work

The bag fully inflates the second time because air from the atmosphere is drawn into the bag next to the stream of air from your lungs. For you science types out there, here’s the technical explanation. In 1738, a scientist named Daniel Bernoulli observed that a stream of fast moving air is surrounded by an area of low atmospheric pressure. In fact, the faster the stream of air moves, the lower the air pressure drops around it. When you blow into the bag, you create a temporary area of low pressure inside the bag and higher pressure air around you in the atmosphere rushes into the bag to equalize things. In other words, air in the atmosphere is drawn into the bag at the same time you are blowing into it.

Firefighters 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.”

In a rescue, first responders also use long, airtight bags and an air compressor to move collapsed walls, huge boulders, and other heavy debris away from victims so they can be saved. The bags between the tables showed you how it works. Science rocks!

Take It Further

The Table Lift Challenge

For this activity, you need:

  • Two bags
  • Two matching desks or tables
  • Two assistants
  • Adult Supervision
  1. Prepare two bags by tying a knot in one end of each bag.
  2. Spread the bags out flat on a table with the open ends hanging well over the opposite edges.
  3. Ask for several people to help you position another identical table upside down on top of the first table. The two bags should be sandwiched in between the tops of the two tables.
  4. Ask each helper to kneel down at the ends of the table and begin blowing into the bags.  This time, however, they do put their mouths on the bag as they blow. Remind them to squeeze the bags closed after each breath so no air escapes.
  5. The force of the air in the bags will slowly cause the inverted table to rise!
  6. Invite more friends to come and sit on the inverted table. Roughly estimate the weight of the table and the people who are sitting on it. Warn your friends not to get their fingers caught in between the tables. As the two people at the ends of the table blow into the Windbags, the table and the people on the table will rise.

The science behind the lifting table can be explained by Pascal’s Law. His experiments with fluids led him to conclude that the pressure exerted on a confined fluid (in this case the air in the bag) exerts equal pressure in all directions: up, down, front, back, and sideways. In other words, the compressed air is exerting pressure underneath the inverted table equally throughout the long bag. This same principle is being applied when you pump up a bicycle tire or when an auto mechanic uses an air lift in a garage.

Our creative team of pencil pushers did a quick calculation and arrived at the conclusion that two Windbags will support up to 2,000 pounds of weight. Remember, firefighters and rescue workers routinely use long, airtight canvas tubes and a large air compressor to lift cars, huge rocks, debris, or other objects out of the way so they can make a successful rescue.

Balloon Structures

Announce to your audience that they have five minutes to work together to build the largest free-standing Windbag structure they possibly can. The structure must only be held up by the Windbags themselves – no one can physically hold up the structure. Note: It would help to do this activity in a gym, a large ballroom, or outside.

Here’s a tip… Loop two rubber bands together to form a “figure eight.” Now hook two Windbags together by slipping the rubber bands over the tied ends of two inflated Windbags. Use more rubber band “figure eights” to connect multiple Windbags and create all kinds of creative structures. It’s a great team building activity for kids and adults alike.



Science Fair Connection

Determine how much Bernoulli’s principle is affected by the size of a bag’s opening. Devise a contraption that adjusts the size accurately or a clever way of measuring it.

Test how long the bags are able to hold onto the air inside of them once inflated.

How is a bag affected by air temperature?

How long can a bag be and still be inflated with one breath? What if you used bigger lungs? a fan?

Steve Spangler Uses Windbags to Set Guinness World Record

Steve used Windbags to demonstrate the power of air at the first annual 9News Weather and Science Day at Coors Field in Denver, Colorado, on May 7, 2009. As part of Weather & Science Day, Steve Spangler Science was awarded the Guinness World Record for the Largest Physics Lesson, with 5,401 participants using their own Windbags to perform their own physics activity. Participants had two minutes to inflate their Windbags, and the news helicopter hovering above the stadium captured the colorful scene. Danny Girton, official adjudicator for Guinness World Records, was on hand to verify the record-breaking event and presented Steve Spangler and his team with an official Guinness World Record certificate at the close of the event.

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