Bernoulli’s Principle Blowing Up Bag

A long plastic bag is inflated with a single quick breath. The fast jet of air lowers pressure at the mouth of the bag and sucks in surrounding air, so room air rushes in with your breath - an application of Bernoulli’s principle.

1. Loosen a long, lightweight plastic bag (e.g., windbag or cut section of a diaper-genie refill) and tie a simple knot in one end.
2. Try the “mouth-on” method: place your lips on the open end and blow 2–3 full breaths. Pinch the neck and slide your hand forward to push the air down. Note how little of the bag fills.
3. For the Bernoulli method, have a helper hold the knotted end level with your mouth. Hold the open end wide with splayed fingers.
4. Position your mouth about 10 in (25 cm) from the opening and blow one long, steady breath into the bag (do not seal your lips to it).
5. Quickly pinch the neck to trap the air and slide your hand forward. Compare the fill to the mouth-on attempt.
6. Repeat, adjusting distance, hand position, and how widely you open the mouth of the bag to maximize the one-breath fill.

Bernoulli's Principle Bag Demo - MrGrodskiChemistry:

📄 Windbag Wonders – Explore Bernoulli’s Principle - Steve Spangler: https://stevespangler.com/experiments/bernoullis-windbags/

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• Do not inhale from the bag; only blow out.
• Keep the work area clear—large bags can whip around.

• Why does standing back from the bag inflate it more than sealing your mouth to the opening?
• How does Bernoulli’s principle relate to the low-pressure region you create with a fast breath?