Egg in a Bottle Experiment: Pressure Does the Pulling

The egg sits on the bottle doing nothing for about twenty seconds, long enough for a child to lose interest. Then it twitches. Then it stretches, narrows, and slides through the neck with a wet slurping noise that nobody ever forgets. This is the egg in a bottle experiment done with hot water instead of a burning match, which is both safer and easier to explain honestly. And the honest explanation matters, because the version everyone repeats, that the flame “uses up the oxygen and makes a vacuum”, is wrong. Burning does not remove much gas. What moves the egg is temperature, and you can prove it with no fire at all.

Key Takeaways

• An adult rinses a glass bottle with boiling water; your kid sits a peeled hard-boiled egg on the mouth and watches the atmosphere push it in.
• It teaches that gas pressure falls as gas cools at fixed volume, and that atmospheric pressure is strong enough to deform food.
• Best fit is ages 7 to 13. The adult handles the boiling water at every age.
• The usual failure is the wrong bottle. The mouth needs to be slightly smaller than the egg’s narrow end, around 3.5 to 4 cm.
• No flame is needed and none should be used. The classic match version works for a reason most explanations get backwards.

What You’ll Need

Item	How much	Where to get it	If you don’t have it
Glass bottle, mouth 3.5–4 cm across	1	An old milk bottle, a juice bottle, a conserve jar	A 1 L glass carafe. The mouth size is the one thing that must be right
Eggs, medium	3 (you’ll waste one)	Supermarket	Contains egg, a common allergen. No substitute
Just-boiled water	300 ml	Kettle	A pan on the hob
Jug for pouring	1	Kitchen	Pour straight from the kettle, adult only
Oven mitt	1	Kitchen	A folded dry tea towel
Cold wet cloth	1	Kitchen	Run the bottle under the cold tap
Ruler or calipers	1	School supplies	A strip of paper, marked

Time: prep 15 min to boil and peel eggs, experiment 20 min, cleanup 5 min Cost: everything is probably in your kitchen Mess level: low, with a wet patch

Do the Experiment

Step 1 — Boil and peel the eggs, then measure them

Hard-boil three eggs for 10 minutes, cool them in cold water and peel them carefully. Measure the narrow end of each with the ruler, and measure the bottle’s mouth.

What you should see: an egg whose narrow end is 1 to 4 mm wider than the bottle’s opening. If the egg drops straight in, your bottle is too wide and nothing interesting will happen. If the egg is twice the width, it will never go.

Step 2 — Have your kid predict, then write it down

Before anything is heated, hand them the egg and the bottle and ask them to try pushing it in by hand. Then ask: what could possibly get this egg into that bottle, and how hard would you have to push?

What you should see: a confident wrong answer, usually involving squeezing. Write it on paper. The prediction is the part that makes the result stick, and it has to come before the result.

Step 3 — Rinse the bottle with boiling water and tip it out

Adult only. Pour about 200 ml of just-boiled water into the bottle, swirl it for a full 45 seconds so the glass and the air inside both get hot, then pour the water out completely.

What you should see: a bottle too hot to hold comfortably, with a little steam at the mouth. Use the mitt. The 45 seconds matters; a quick splash heats the water but not the air.

Step 4 — Seat the egg on the mouth, narrow end down

Immediately set the egg on the opening with its pointed end in the hole, and press gently once to make a seal. Then let go and leave it completely alone.

What you should see: nothing for 15 to 30 seconds, then a small shudder. Over the next half-minute the egg elongates, squeezes and pops through, landing at the bottom with a slap. If it stalls halfway, wrap the cold wet cloth around the bottle and it will finish.

Step 5 — Get the egg out again, which is the better half

Turn the bottle upside down and shake gently until the egg’s narrow end seats in the neck from the inside. Now hold the bottle under a hot tap, or have an adult pour hot water over the outside while you keep it inverted.

What you should see: the egg is pushed back out and lands in your hand. You have run the experiment backwards by heating the trapped air instead of cooling it, which is the clearest proof that temperature is the variable doing the work.

What’s Actually Going On

The air sealed inside the bottle obeys the ideal gas law, pV = nRT, which HyperPhysics states compactly. The volume is fixed by the glass and the amount of gas is fixed by the egg sitting on the hole, so pressure and absolute temperature rise and fall together. Heat the air to about 95 °C, which is 368 kelvin, then let it fall to a room at 25 °C, or 298 kelvin, and the pressure drops to 298/368 of what it was. That is a fall of roughly 19 per cent, or about 19 kilopascals below the 101 kilopascals of outside air that the NOAA JetStream pages give as the sea-level standard.

Nineteen kilopascals does not sound like much until you multiply by area. A 4 cm mouth has an area of about 0.0013 square metres, so the net inward force on the egg is around 24 newtons, the weight of a 2.4 kilogram bag of flour pressing down on a soft object the size of a plum. The egg deforms, loses its seal for a moment, and the rush of air past it carries it the rest of the way. If any water is left in the bottle, the condensing vapour lowers the pressure further, which is why a damp bottle works better than a bone-dry one.

Now the correction, and it is a good one to be able to make at a dinner table. The traditional version drops a burning match or a scrap of lit paper into the bottle, and the explanation handed down with it is that the flame consumes the oxygen and leaves a vacuum. That is not what happens. Burning carbon turns each oxygen molecule into a carbon dioxide molecule, so the number of gas molecules barely changes. Hydrogen in the fuel produces water vapour, which does condense and does help a little. But the dominant effect is the same as yours: the flame heats the air violently, the air expands and some escapes past the egg, and then the remaining gas cools and contracts. The flame is a fast heater, not an oxygen vacuum.

This matters beyond pedantry. If the oxygen story were right, the trick would only work once per bottle and would not reverse. Your Step 5 reverses it, with no chemistry involved at all.

How to Explain It to Your Kid

Ages 5–8: The air is squeezing from outside

Have them push the egg with a finger first, so they know how stubborn it is. Then let them watch. Afterwards, tell them that the hot bottle was full of fat, puffed-up air, and when the air got cold it pulled in on itself and left a gap. The air outside the bottle rushed to fill the gap and took the egg with it.

Then do the reverse step and let them catch the egg. At this age the fact that it goes both ways is more convincing than any explanation.

Ages 9–12: Hot gas pushes harder than cold gas

Introduce the rule in one sentence: in a sealed container, hotter gas pushes harder and colder gas pushes less. Have them time how long the egg takes with a hot cloth versus a cold cloth around the bottle, two trials each. That is enough to show the rate depends on how fast you cool it, which is a real experimental result from four data points. Our piece on putting a balloon in the freezer is the same relationship with a flexible container instead of a rigid one.

Ages 13+: Put numbers on it and check them

Give them pV = nRT, have them estimate the air temperature after swirling (a cheap thermometer in the bottle gets within a few degrees), and work out the expected pressure drop and the resulting force on the egg. Then compare: does 24 newtons seem like enough to deform a boiled egg? They can test that directly by stacking weights on an egg until it yields. Matching a calculation to a measurement is the whole point. Pair it with the can crush experiment to see the difference between cooling a gas and condensing a vapour.

The question to ask: “If we did this with a balloon stretched over the mouth instead of an egg, which way would the balloon go, and why?”

Why Teaching This Early Pays Off

This experiment attacks one specific confusion that persists into adulthood: the idea that a vacuum pulls. Nothing pulls. A region of low pressure does not reach out; the higher pressure elsewhere pushes. Children who get this straight have a much easier time later with straws, syringes, siphons, suction cups, breathing and weather maps, all of which are usually taught with the word “suction” doing damage.

It also gives a child a correction they can make to an adult, which is unusually motivating. The burning-oxygen explanation is in books, on posters and in science shows. Being able to say “actually it’s the temperature, and here’s how you can tell” is a real piece of intellectual independence, and it was earned from an observation rather than handed over.

Keep the claim modest: one experiment does not change how a child thinks. What helps is the structure. Asking for a prediction before the lid goes on is the Predict-Observe-Explain sequence White and Gunstone described in Probing Understanding, and the prediction only counts if it comes first. It is also worth noting the counterweight: Kirschner, Sweller and Clark argued in 2006 that leaving learners to discover principles without guidance does not work, so talk through the mechanism rather than hoping the egg speaks for itself.

Before You Start: What Parents Should Know

Best age	7 to 13. Younger children enjoy it but cannot hold the gas-law reasoning; teenagers should do the arithmetic or it feels like a party trick.
Supervision	Adult pours all boiling water and handles the hot bottle. The child seats the egg once the bottle is in place on a stable surface.
Real hazards	Boiling water and hot glass. A thin or chipped glass bottle can crack when filled with boiling water, so warm it with hot tap water first and discard any bottle with a chip. Eggs are a common allergen. Do not use a bottle that previously held anything other than food or drink.
Don’t	Don’t use a flame, lit paper or a match: it is unnecessary and it is the one part of this experiment that has actually caused injuries. Don’t use a plastic bottle, which deforms instead of holding its volume. Don’t eat the egg afterwards; it has been handled and sat at room temperature.

If anyone is scalded, cool under cool running water for 20 minutes and follow the NHS advice on burns and scalds.

When It Doesn’t Work

• The egg sits there for five minutes doing nothing. You did not heat the air long enough. Forty-five seconds of swirling with genuinely boiling water, not hot tap water. Then speed the cooling with a cold wet cloth.
• The egg drops straight in. Your bottle’s mouth is too wide. This is the most common equipment problem, and the fix is a different bottle, not a different egg. Measure before you boil.
• The egg gets stuck halfway and stops. It has lost its seal, so air is leaking past. Lift it off, moisten the mouth and the egg with a little water, reheat and reseat.
• The bottle cracked. Thermal shock. Always pre-warm with hot tap water, never pour boiling water into a cold thick-walled bottle, and inspect for chips first.
• The egg won’t come back out. It needs to seat narrow-end-first into the neck from the inside, which takes some patient shaking with the bottle inverted. Then heat the outside. Blowing hard into an inverted bottle also works and children usually prefer it.

Take It Further With the Egg in a Bottle Experiment

Measure the cooling rate against the time taken. Run four trials: bottle left in still air, bottle fanned, bottle wrapped in a cold wet cloth, bottle under cold running water. Time each egg’s entry from the moment it is seated. Plot time against cooling method. You are measuring how pressure difference builds, and the ordering will be consistent.

Find the pressure threshold. Instead of boiling water, use water at 50 °C, 70 °C and 95 °C, measured with a thermometer. There will be a temperature below which the egg never goes in. Work out the predicted pressure drop at that temperature and you have found the force needed to deform that egg, which you can then check with weights.

What to Watch For Over the Next 3 Months

• Week 4: they correct someone about “suction”, or notice a jar lid that is hard to open after being in the fridge.
• Month 2: the word pressure appears in an explanation they weren’t asked for, often about ears on a plane or a stuck drawer.
• Month 3: they propose their own variant, usually involving a different object on the bottle mouth. Let them try it; most of them work.

Frequently Asked Questions

Does this work with a cold boiled egg and a hot bottle, or does the egg need to be warm?

The egg’s temperature barely matters. What matters is the temperature of the air sealed in the bottle. A fridge-cold egg actually helps slightly, because it cools the air near the mouth faster.

Why do most instructions use a burning match?

Because it heats the air very quickly and the demonstration is fast. The hot-water version is slower, takes a bit more patience, and avoids dropping fire into glass near a child’s face. Given that the mechanism is thermal either way, the water version is the better trade.

Is the egg safe to eat afterwards?

Treat it as not for eating. The procedure itself is food-grade, but the egg has been handled, measured, squeezed through a bottle neck and left at room temperature. Compost it or bin it.

What if my bottle’s mouth is a bit too big?

Use a smaller egg, or a quail egg with a correspondingly narrow bottle. You can also use a peeled hard-boiled egg trimmed slightly, though that is fiddly. Changing the bottle is almost always easier than changing the egg.

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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. Georgia State University. “Ideal Gas Law.” HyperPhysics. http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/idegas.html
2. National Oceanic and Atmospheric Administration, National Weather Service. “Air Pressure.” JetStream. https://www.noaa.gov/jetstream/atmosphere/air-pressure
3. NASA Glenn Research Center. “Earth Atmosphere Model, Metric Units.” https://www.grc.nasa.gov/www/k-12/airplane/atmosmet.html
4. National Institute of Standards and Technology. “Thermophysical Properties of Fluid Systems.” NIST Chemistry WebBook. https://webbook.nist.gov/chemistry/fluid/
5. White, R., & Gunstone, R. (1992). Probing Understanding. Falmer Press.
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. National Health Service (UK). “Burns and scalds.” https://www.nhs.uk/conditions/burns-and-scalds/