Does Air Have Mass? Experiment With a Balloon Balance

Run the famous version of this and it will probably disappoint you, and that is the most interesting thing about it. Hang two inflated balloons from a stick, pop one, and the stick is supposed to tip. Usually it barely moves. Thousands of articles show it working anyway. The reason it fails is worth more than the result it was supposed to give: a balloon full of air is also displacing air, and the two effects nearly cancel. So here is a does air have mass experiment that gives a clean, repeatable number instead: weigh a basketball, pump it up, weigh it again, and watch it gain about five grams.

Key Takeaways

• You’ll run the classic balloon balance, see it underperform, then weigh a ball before and after pumping to get a measurable mass gain of several grams.
• It teaches that air has mass, roughly 1.2 grams per litre, and that a scale measures weight minus buoyancy.
• Best fit is ages 6 to 12. The arithmetic suits the older end; the ball-weighing works for everyone.
• The usual failure is the balloon balance itself, and this article explains why rather than pretending otherwise.
• Latex balloon pieces are a serious choking hazard for small children. Clear up every fragment.

What You’ll Need

Item	How much	Where to get it	If you don’t have it
Basketball, football or volleyball with a valve	1	Sports cupboard	Any inflatable ball that holds its shape when deflated
Ball pump with needle	1	Sports shop	A bike pump with a ball adapter
Digital scale reading to 0.1 g	1	Kitchen or a jewellery scale online, ~$10	A 1 g kitchen scale works but the result is less convincing
Party balloons	4	Supermarket	Choking hazard for under-threes. Latex allergy risk
Wooden dowel or bamboo skewer, 40 cm	1	Garden or kitchen	A straight stick, a ruler
String	1 m	Drawer	Thread, dental floss
Sticky tape	1 roll	Drawer	Any tape
Tape measure	1	Drawer	A ruler, for working out the ball’s volume
Pin	1	Sewing kit	Adult handles this

Time: prep 10 min, experiment 30 min, cleanup 5 min Cost: around $10 if you buy a 0.1 g scale, which is worth owning Mess level: low

Do the Experiment: Does Air Have Mass? Experiment Steps

Step 1 — Get the prediction on paper first

Ask: does air have mass? Then ask the sharper version: how much do you think the air in this room weighs? Write the answer down, including the guess in kilograms.

What you should see: almost everyone says air has mass but guesses far too low for the room. Children often say a few grams. Adults often say a kilogram. The real answer for a small bedroom is around 60 kilograms, which you will calculate in Step 5.

Step 2 — Build the balloon balance and watch it struggle

Inflate two balloons to the same size, tape one to each end of the dowel, and hang the dowel from a string so it balances level. Adjust until it sits still. Then have an adult pop one balloon with the pin.

What you should see: very little. The stick might tip slowly, or it might not move at all, or it might tip the wrong way because the popped balloon’s rubber ended up heavier or lighter than the other’s. Do not force this result. Note what happened honestly and move on.

Step 3 — Weigh the ball fully deflated

Press the air out of the ball as completely as you can while keeping its shape, and weigh it on the 0.1 g scale. Do this three times, lifting it off and replacing it between readings.

What you should see: three readings within about 0.2 g of each other. Write all three down and average them. This is your baseline, and taking three readings rather than one is what makes the next step mean anything.

Step 4 — Pump it to the printed pressure and weigh again

Find the pressure printed near the valve, often around 8 psi for a basketball or 0.8 bar for a football, and pump to it. Weigh three times again.

What you should see: a gain of roughly 4 to 6 grams for a basketball, or 5 to 7 grams for a football. It is unmistakable on a 0.1 g scale and still visible on a 1 g one. The ball looks identical, occupies the same space, and is now measurably heavier.

Step 5 — Do the arithmetic and then weigh the room

Air at sea level and 15 °C has a density of about 1.225 grams per litre. Work out the ball’s volume from its circumference, multiply by the gauge pressure in atmospheres, and multiply by 1.2 g per litre. Then measure your room and multiply length by width by height in metres, times 1,225 grams per cubic metre.

What you should see: a predicted ball gain within a gram or so of what you measured, and a room full of air weighing somewhere between 50 and 100 kilograms. That second number is the one your kid will repeat at school.

What’s Actually Going On

Air is matter. At sea level and 15 °C its density is 1.225 kilograms per cubic metre, which is the reference value in NASA Glenn’s standard atmosphere model, and it falls off with altitude as NOAA’s JetStream pages on the atmosphere describe. One litre weighs about 1.2 grams, which sounds negligible until you multiply by the volume of a room.

So why does the balloon balance fail? Because a scale, or a balance, does not measure mass directly. It measures weight minus the buoyant force, and the buoyant force equals the weight of the air the object displaces. This is not a nuisance invented for this article; it is a standard correction in precision weighing, set out by Schoonover and Jones in Analytical Chemistry in 1981, and national metrology institutes including NIST’s weights and measures programme build it into their procedures.

Now the numbers, which make the failure obvious. A party balloon inflated to 25 cm across holds about 3 litres. Its internal gauge pressure is small, typically only two to four kilopascals above the room, so the air inside is only about 2 to 4 per cent denser than the air outside. The air it contains therefore weighs around 3.7 grams. But the inflated balloon displaces 3 litres of room air, which weighs about 3.6 grams, and that buoyancy is subtracted from the reading. Net effect: roughly a tenth of a gram. No stick-and-string balance in a kitchen can see a tenth of a gram, especially with air currents and with rubber that stretches unevenly.

The ball works because its volume does not change. Deflated or inflated, a basketball occupies roughly the same 7.5 litres, so the buoyant force is identical in both measurements and cancels out of the comparison. What changes is the density of the air inside: at 8 psi gauge, about 0.55 atmospheres above ambient, the ball holds 55 per cent more air mass than it would at room pressure. That extra mass is 7.5 litres times 0.55 times 1.2 grams per litre, which is about 5 grams. You measured it, and the arithmetic agrees.

There is a nice corollary worth saying out loud. A helium balloon on a scale appears to weigh less than nothing, in the sense that it pulls upward. Helium does have mass, about 0.17 grams per litre, but it displaces air weighing 1.2 grams per litre, so the net is upward. Nothing about buoyancy says the floating object is massless. It says the surrounding fluid is heavier.

How to Explain It to Your Kid

Ages 5–8: Air is stuff

Air is a thing, not nothing. It is made of tiny bits that are too small to see, and if you squash a lot of them into a ball, the ball gets heavier. Let them hold the deflated ball, then pump it with you, then hold it again while watching the scale.

Then tell them the room number. Sixty kilograms of air in a bedroom is roughly the weight of a grown-up, floating invisibly around them, and it is the single most repeatable fact a seven-year-old will take from this.

Ages 9–12: A litre of air weighs 1.2 grams

Give them the number and let them do the room calculation themselves with a tape measure. Then explain why the balloon test failed: the balloon got heavier and also got bigger, and getting bigger pushes the balloon up, so the two almost cancel. That is a real idea, delivered plainly, and it is more honest than letting them think their experiment was botched. Our note on putting a balloon in the freezer uses the same gas properties a different way.

Ages 13+: Measure the buoyancy correction

Give them Archimedes’ principle and the formula apparent weight = mg − ρ_air·V·g. The investigation: inflate four balls to 2, 4, 6 and 8 psi gauge, measured with a pressure gauge, and weigh each. Plot mass gain against gauge pressure. You should get a straight line through the origin with a slope equal to the ball’s volume times 1.2 g per litre per atmosphere, which means you can recover the ball’s internal volume from the weighing alone and then check it against the circumference measurement. Two independent routes to the same number is what makes this a real experiment. Pair it with crushing a can with air pressure for the force side of the same substance.

The question to ask: “If we weighed a sealed empty bottle, then pumped air into it, would the reading change? What if the bottle were made of balloon rubber instead of plastic?”

Why Teaching This Early Pays Off

The belief that air is nothing is one of the most durable ideas children hold, and it blocks a surprising amount of later understanding: pressure, weather, buoyancy, breathing, aerodynamics, gas laws and chemical reactions involving gases all depend on accepting that air is matter with mass. Children’s models of invisible systems tend to be internally consistent and wrong, and they get patched rather than replaced, which Vosniadou and Brewer documented for models of the Earth. A measured five grams is harder to patch around than an assertion.

The buoyancy correction has a second payoff that is really about scientific practice. Your kid will have run an experiment that is all over the internet and found that it does not work, and then found out why, and then designed a version that does. That sequence, failure then diagnosis then redesign, is what research actually feels like, and it is almost never on offer in a school worksheet.

Keep the claim proportionate. One session does not change a trajectory. What it can do is give a concrete anchor, and the National Research Council’s framework names using mathematics and computational thinking as one of eight core practices; predicting a five-gram gain and then measuring it is a direct instance. The room calculation is the part that tends to stick for years.

Before You Start: What Parents Should Know

Best age	6 to 12. Six-year-olds pump and watch the scale; eleven-year-olds do the room calculation and the buoyancy explanation.
Supervision	Light, except for the pin and the pump. An adult pops the balloon and pumps the ball to avoid over-inflation.
Real hazards	Fragments of burst latex balloon are a serious choking hazard for children under about eight, and balloons are among the most common causes of toy-related choking deaths. Count the pieces and clear them all, and follow the AAP’s choking prevention guidance. Latex allergy is real; use mylar balloons or skip Step 2 if anyone is affected. Pump needles are sharp. An over-inflated ball can burst loudly.
Don’t	Don’t exceed the pressure printed on the ball. Don’t let a child under three anywhere near balloons, inflated or not. Don’t use a compressor or a petrol-station air line on a sports ball.

When It Doesn’t Work

• The balloon balance tips the wrong way. Entirely expected. The rubber of two balloons differs in mass by more than the air difference you are trying to detect. This is a result, not a mistake: record it and explain it.
• The ball shows no mass gain. Your scale is not sensitive enough, or the ball was already partly inflated at the baseline reading. Press it as flat as it will go while keeping its shape, and use a 0.1 g scale.
• Readings jump around by a gram or more. Air currents, a wobbly table, or your hands near the pan. Close the windows, put the scale on a solid surface, and take three readings each time.
• The ball gains far more than 6 grams. Water from a damp pump or from your hands, or the ball was wet. Dry everything and repeat. Condensation from a humid day can add a gram or two.
• Your room calculation gives an absurd number. Check units. Cubic metres times 1,225 grams gives grams; it is easy to be out by a factor of a thousand, and spotting that is itself a useful skill.

Take It Further

Pressure against mass, five points. Use a pressure gauge and weigh the ball at 2, 4, 6, 8 and 10 psi gauge, three readings each. Plot mass gain against pressure. A straight line through the origin confirms the ideal-gas relationship, and its slope gives you the ball’s volume without ever measuring its size.

Weigh the buoyancy itself. Put an inflated party balloon on the scale, record the reading, then deflate it and weigh the limp balloon. The difference should be close to nothing, which is the buoyancy result stated as a measurement. Then do the same with a helium balloon, holding it down on the pan, and the reading will be lower than the empty pan. That pair of results explains flight in hot-air balloons.

What to Watch For Over the Next 3 Months

• Week 4: they tell someone how much the air in a room weighs, usually getting the number right.
• Month 2: buoyancy appears in an explanation of something else, often a boat, a hot-air balloon or why a helium balloon sinks when it gets cold.
• Month 3: they notice an experiment online that would not work for a reason they can name. That is the skill this article is really for.

Frequently Asked Questions

Why do so many articles show the balloon balance working?

Some use balloons inflated to very different sizes, which changes the rubber’s mass and the balance arm rather than demonstrating the mass of air. Some are filmed with a hand nearby. Some genuinely see a tiny tip from a stiff, over-inflated balloon, which does compress its air more. It is a marginal experiment presented as a clear one.

Can we use a kitchen scale instead of a 0.1 gram one?

Yes for the ball. A 5 gram gain registers on a 1 gram scale, though you will see less consistency between repeats. For the buoyancy comparison in the extension, a 0.1 gram scale is necessary, and a jewellery scale costs about the price of a takeaway.

Does air weigh less at altitude?

Yes, substantially. Air density falls with height, so a ball pumped to the same gauge pressure in Mexico City gains slightly less mass than at sea level, and the air in a room there weighs about a quarter less than in a room of the same size by the coast.

If air has mass, why doesn’t it crush us?

It does push on us, with about 101 kilopascals, which is over ten tonnes per square metre. We do not notice because it pushes equally from all sides and because the pressure inside our bodies matches it. Take the inside pressure away and the result is dramatic, which is what a crushed drinks can demonstrates.

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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. “Earth Atmosphere Model, Metric Units.” https://www.grc.nasa.gov/www/k-12/airplane/atmosmet.html
2. National Oceanic and Atmospheric Administration, National Weather Service. “The Atmosphere.” JetStream. https://www.noaa.gov/jetstream/atmosphere
3. Schoonover, R. M., & Jones, F. E. (1981). “Air buoyancy correction in high-accuracy weighing on analytical balances.” Analytical Chemistry, 53(6), 900–902. doi:10.1021/ac00229a036
4. National Institute of Standards and Technology. “Weights and Measures.” https://www.nist.gov/pml/weights-and-measures
5. Georgia State University. “Fluid Concepts.” HyperPhysics. http://hyperphysics.phy-astr.gsu.edu/hbase/fluid.html
6. American Academy of Pediatrics. “Choking Prevention.” HealthyChildren.org. https://www.healthychildren.org/English/health-issues/injuries-emergencies/Pages/Choking-Prevention.aspx
7. Vosniadou, S., & Brewer, W. F. (1992). “Mental models of the earth: A study of conceptual change in childhood.” Cognitive Psychology, 24(4), 535–585. doi:10.1016/0010-0285(92)90018-W
8. National Research Council. (2012). A Framework for K-12 Science Education. National Academies Press. doi:10.17226/13165