Bernoulli Ping Pong Ball Experiment: Float It on Air

A ping-pong ball hanging in mid-air above a hair dryer is one of the best five seconds of physics available in a house. Tilt the dryer and the ball stays with the jet rather than falling out of it, which is the part that makes people say “how?” The standard answer, that fast-moving air has low pressure and sucks the ball back in, is the version almost everyone repeats and it does not survive scrutiny. The real account is about momentum, jet shape and a feedback loop, and it is more interesting. This Bernoulli ping pong ball experiment is worth running precisely because getting the explanation right takes more care than getting the ball to float.

Key Takeaways

• You’ll hover a ping-pong ball in a hair dryer’s cool airstream, tilt the jet, and feel the sideways restoring force with your own fingers.
• It teaches that a jet’s speed falls with distance, that drag can balance weight at a stable height, and that a curved object deflects a jet and feels the reaction.
• Best fit is ages 6 to 12, with the careful explanation aimed at the top of that range and at the adult.
• The usual failure is using the heat setting, which deforms the ball and is a burn risk. Cool air only.
• The popular “faster air means lower pressure so the ball is sucked in” sentence is a misuse of Bernoulli’s equation. The correct version is below and is not much harder.

What You’ll Need

Item	How much	Where to get it	If you don’t have it
Hair dryer with a cool or no-heat setting	1	Bathroom	A vacuum cleaner with a blow port; a leaf blower works outdoors but is loud
Ping-pong balls	3	Sports shop, cheap	A small polystyrene craft ball, which is lighter and hovers higher
Plastic funnel, 8–10 cm wide	1	Kitchen	A paper cone taped into shape, with a drinking straw in the tip
Drinking straw	1	Kitchen	The funnel stem alone
Ruler or tape measure	1	School supplies	A wall marked with sticky notes
Protractor	1	School supplies	A printed angle sheet
Kitchen scale reading to 0.1 g	1	Kitchen	A ping-pong ball’s mass is 2.7 g by rule, so you can use that figure
Phone for slow-motion video	1	Pocket	Watch carefully instead

Time: prep 5 min, experiment 25 min, cleanup 2 min Cost: everything is probably in your house Mess level: low, but it is loud

Do the Experiment: The Bernoulli Ping Pong Ball Experiment

Step 1 — Hover the ball straight up

Plug in the dryer, set it to cool and high speed, point it vertically upward and hold it steady. Place the ball into the stream about 10 cm above the nozzle and let go.

What you should see: the ball drops a little, catches, and then sits bobbing in the stream, typically 10 to 25 cm above the nozzle depending on your dryer. It wobbles and spins. It does not shoot away, and it does not fall.

Step 2 — Find the hover height, then change the airflow

Measure the height of the ball above the nozzle with the ruler. Now switch to the low speed setting and measure again.

What you should see: lower airflow means a lower hover height, and the ball may fall out entirely. There is a specific height at which the air is moving just fast enough to hold up 2.7 grams, and that height moves when you change the speed. Write both numbers down.

Step 3 — Tilt the jet and keep going

Slowly tilt the dryer away from vertical: 15°, then 30°, then 45°, measuring with the protractor. Keep the airflow the same.

What you should see: the ball stays in the jet well past the point where you expect it to fall out, often to 40° or more. It sits slightly below the jet’s centre line. At some angle it finally escapes, and that angle is a repeatable number for your dryer.

Step 4 — Push it out and feel the force

With the ball hovering, slowly press a finger against its side to push it out of the stream. Then let go while it is still partly in the jet.

What you should see: resistance. You can feel the ball pushing back toward the jet, and when you release it, it snaps back to the middle. That restoring force is the thing to explain, and feeling it with a finger is better than watching it.

Step 5 — Try the funnel version with lung power

Put the ball inside the funnel, tip the funnel so the opening faces slightly downward, and blow hard and steadily up through the stem. Then stop blowing.

What you should see: while you blow, the ball stays in the funnel instead of being pushed out, even pointing downward. Stop and it drops immediately. A child can do this one with no appliance at all, and it is the cleanest demonstration of the sideways effect because the funnel wall shows you where the air is going.

What’s Actually Going On

Start with the easy half. A hair dryer produces a jet of air that slows down as it travels, because it spreads out and drags still room air along with it, a process called entrainment. So the air speed at 5 cm above the nozzle is higher than at 25 cm. The ball sits in that stream and experiences aerodynamic drag pushing it upward, and drag grows with the square of the relative air speed. Too high and the air is too slow, so the ball falls; too low and the air is too fast, so it rises. The equilibrium is stable because the feedback has the right sign, which is why Step 2 gives a definite, measurable height rather than the ball shooting off or dropping.

Now the harder half, the sideways force, and this is where popular explanations go wrong. The usual claim is that air moving fast past the ball has lower pressure, so the surrounding still air pushes the ball back in. Bernoulli’s equation does relate higher speed to lower pressure, but it only does so between points along the same streamline in the same steady flow. A free jet blowing into a still room is not one flow that you can trace a streamline through from the jet’s core out to the quiet air beside it; the jet and the room have different total pressures, and across most of a free jet the static pressure is close to ambient anyway. Applying Bernoulli across that boundary is the classic error, and the aerodynamicist Charles Eastlake made the same point about lift in The Physics Teacher in 2002, as does NASA Glenn’s discussion of Bernoulli and Newton, which exists mainly because this confusion is so widespread.

The honest account is a momentum argument. When the ball drifts off the jet’s axis, the jet no longer hits it symmetrically. The flow attaches to the ball’s curved surface and gets deflected away from the ball, which means the jet’s momentum has been turned. By Newton’s third law, turning the air one way pushes the ball the other way, which is inward, toward the jet. The curvature of the flow around the ball also requires a pressure gradient across the streamlines, with lower pressure on the inside of the curve, so there is a genuine pressure difference. That is Bernoulli-adjacent reasoning applied correctly, within the flow rather than across its edge. Entrainment adds a third contribution: the ball partially blocks the jet’s ability to drag in room air on the side nearest the jet, which lowers pressure slightly on that side.

So what should you tell a child? That the ball is riding on moving air that pushes it up, and that when it leans out of the stream it bends the air sideways, and bending air sideways makes the air push the ball back. That is correct, requires no equation, and does not need to be unlearned later. The thing not to say is that the fast air sucks.

How to Explain It to Your Kid

Ages 5–8: It is surfing on a push

Air is really there, even though you cannot see it, and a dryer throws a river of it upward. The ball sits on the river like a cork sits on a fountain. Have them put a hand into the stream at 5 cm and then at 30 cm so they can feel that the push gets weaker further up; that is why the ball picks one height and stays there.

Then let them do the funnel. Blowing while the funnel points down, and the ball refusing to fall, is a better memory than anything a dryer does.

Ages 9–12: Weak higher up, strong lower down

Introduce drag as the push air gives a moving object, and the idea that it gets stronger the faster the air moves. Then use their own two measurements from Step 2 to make the point: the ball sat lower when the air was slower, because it had to go down to where the air was still fast enough. Our write-up of how a paper aeroplane really works uses the same honest treatment of lift.

For the sideways force, use their hand: hold a flat palm in the jet and tilt it, and feel the push change direction. The ball does the same thing with a curved surface.

Ages 13+: State Bernoulli’s conditions, then use momentum

This is the age to meet a famous equation along with its fine print. Bernoulli’s relation assumes steady, incompressible, inviscid flow along a streamline, and the whole point of this experiment is that one of those assumptions fails in the obvious application. Have them write out why, then do the momentum version: estimate the jet velocity by timing a light tracer, compute the momentum flux through the ball’s cross-section, and check it against the ball’s 2.7 gram weight. The numbers come out in the right ballpark, which is satisfying, and the discrepancy is honest information about how much of the jet actually hits the ball. For a related air-cushion effect, see building a hovercraft from a CD and a balloon.

The question to ask: “If we used a heavier ball of the same size, would it hover higher or lower, and why?”

Why Teaching This Early Pays Off

Fluid behaviour is everywhere a child looks and it is almost universally taught badly. The same loose Bernoulli sentence is used to explain aeroplane wings, shower curtains, curveballs, chimneys and this ball, and in several of those cases it gives the wrong answer or the wrong magnitude. Meeting a correct momentum-based account early means a student is not carrying a broken tool into secondary physics.

There is a broader payoff too, and it is about epistemics rather than aerodynamics. This is a rare chance to show a child that a widely repeated scientific explanation can be wrong without the underlying phenomenon being in any doubt. The ball really does hover. The usual reason really is a misapplication. Holding both of those at once is a sophisticated move, and a hovering ping-pong ball is an unusually friendly place to practise it.

Be careful with the learning claims. Kirschner, Sweller and Clark argued in 2006 that leaving learners to infer principles without guidance does not work, and that applies sharply here: nobody discovers the momentum argument by watching a ball bob. The adult has to say it. The National Research Council’s framework names engaging in argument from evidence as one of eight core practices, and comparing two candidate explanations against the same observation is exactly that.

Before You Start: What Parents Should Know

Best age	6 to 12 for the activity. The careful explanation is really for the adult to deliver, and a 13-year-old can take the full version.
Supervision	Adult plugs in and holds the dryer. Keep it well away from sinks, baths and any water. Never modify or open the appliance.
Real hazards	Use the cool setting only. The heat setting will soften and deform a ping-pong ball and the nozzle gets hot enough to burn. A hair dryer is loud, around 80 decibels close up, so keep it away from ears and limit the session. Do not point it at anyone’s eyes. Ping-pong balls are a choking hazard for toddlers and are also flammable, so keep them away from any flame.
Don’t	Don’t substitute a heat gun or a hot-air paint stripper, which some videos use. Don’t use the dryer near a bathtub or sink. Don’t let a child hold the dryer and reach for the ball at the same time.

When It Doesn’t Work

• The ball flies straight out of the stream. Your jet is too narrow or too fast for the ball. Move the ball higher before releasing, or switch to the low speed setting, or use a wider nozzle by removing the concentrator attachment.
• The ball just falls. Airflow too low, or the dryer’s nozzle is too wide and the jet has spread out. Try the high setting and get the ball closer to the nozzle on release.
• It hovers for a second and drops. You are moving the dryer. Brace your wrist against a table or clamp the dryer to a chair back; a wobbling jet loses the ball.
• The tilt test fails immediately. Tilt in small steps and let the ball settle between each one. Jumping straight to 45° throws the ball out before the restoring force has a chance to act.
• The funnel version does nothing. Blow harder and more steadily, and check the funnel is smooth inside. A funnel with ridges or a sharp step disrupts the attached flow that makes the trick work.

Take It Further

Hover height against mass. Add small pieces of modelling clay inside a ping-pong ball through a pinhole, weighing the ball each time, and record the hover height. Plot height against mass. Heavier balls sit lower, and the curve tells you how fast the jet decays with distance, which is a real fluid-mechanics measurement made with a hair dryer.

Find the escape angle. Measure the maximum tilt at which the ball stays in the jet, five trials, and average. Then repeat with a polystyrene ball of the same diameter. The lighter ball should hold on at a greater angle, because the sideways restoring force is similar while the weight it has to fight is smaller.

What to Watch For Over the Next 3 Months

• Week 4: they notice a leaf or a bit of litter held up by a vent, or a fountain holding a ball in a shop display.
• Month 2: the word drag or the idea of air pushing turns up in a conversation about cycling, parachutes or a car’s shape.
• Month 3: they query a “fast air has low pressure” explanation they hear elsewhere, or ask what Bernoulli’s equation actually requires. That question is the whole article arriving home.

Frequently Asked Questions

Is it really not Bernoulli, then?

Bernoulli’s relation is correct physics and it does play a part, specifically in the pressure gradient across the curved streamlines around the ball. What is wrong is comparing a point inside a free jet with a point in the still room, which the equation does not license. So the answer is: Bernoulli applies within the flow, not across its edge.

Why does the ball spin?

Because the airflow around it is never perfectly symmetric, so there is always a small torque. The spin then produces a sideways force of its own, the Magnus effect, which is why the ball often circles rather than sitting dead still.

Can we do this without a hair dryer?

Yes. The funnel-and-lungs version in Step 5 shows the sideways restoring force with no appliance at all, and it is arguably the better demonstration. You can also hover a ball over an upward-facing fan, though the jet is wider and weaker so a lighter polystyrene ball works better.

Why does it stay in the jet when tilted but fall out if I tilt too far?

Because the sideways restoring force has a maximum. Beyond a certain angle, the component of gravity pulling the ball out of the jet exceeds the largest inward force the deflected air can supply, and the ball leaves. That crossover angle is a genuine measurement, and Step 3 finds it.

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About the author

Ricky Flores is the founder of HiWave Makers and an electrical engineer with 15+ years of experience building consumer technology at Apple, Samsung, and Texas Instruments. He writes about how kids learn to build, think, and create in a tech-saturated world. Read more at hiwavemakers.com.

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Sources

1. NASA Glenn Research Center. “Bernoulli and Newton.” Beginner’s Guide to Aeronautics. https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/bernoulli-and-newton/
2. Eastlake, C. N. (2002). “An aerodynamicist’s view of lift, Bernoulli, and Newton.” The Physics Teacher, 40(3), 166–173. doi:10.1119/1.1466553
3. Smith, N. F. (1973). “Bernoulli, Newton, and dynamic lift, Part II.” School Science and Mathematics, 73(4), 327–335. doi:10.1111/j.1949-8594.1973.tb09040.x
4. Georgia State University. “Fluid Concepts.” HyperPhysics. http://hyperphysics.phy-astr.gsu.edu/hbase/fluid.html
5. The Physics Classroom. “Momentum, Collisions and Explosions.” https://www.physicsclassroom.com/tutorial/momentum-collisions-and-explosions
6. Kirschner, P. A., Sweller, J., & Clark, R. E. (2006). “Why minimal guidance during instruction does not work.” Educational Psychologist, 41(2), 75–86. doi:10.1207/s15326985ep4102_1
7. National Research Council. (2012). A Framework for K-12 Science Education. National Academies Press. doi:10.17226/13165
8. NASA Glenn Research Center. “Earth Atmosphere Model, Metric Units.” https://www.grc.nasa.gov/www/k-12/airplane/atmosmet.html