Spinning Egg Experiment: Raw or Boiled? Spin to Find Out

Here is the test nobody tells you about. Spin an egg on the counter, stop it dead with one finger for a second, then take your finger away. If it sits there, it is boiled. If it quietly starts turning again on its own, it is raw, because the liquid inside never stopped.

That is the whole spinning egg experiment in one move, and unlike the usual “boiled ones spin better” version, it needs no judgement about what counts as better. It is a yes or no.

Key Takeaways

• You will sort a mixed batch of eggs into raw and boiled using three spin tests, then crack them to check.
• The concept is rigid-body rotation: a solid interior turns with the shell, a liquid one does not.
• Best for ages 6 to 12. Six-year-olds can do the spinning and the sorting; the moment-of-inertia idea arrives around 11.
• The detail that decides everything: boil the eggs long enough. A 6-minute egg behaves like neither.
• Never microwave an egg in its shell. They burst, and the burst happens after you take it out.

What You’ll Need

Item	How much	Where to get it	If you don’t have it
Eggs	6, all the same size	Supermarket	Any eggs; keep sizes matched so the comparison is fair
Saucepan	1	Kitchen	Any pot that holds the eggs in one layer
Smooth hard table or counter	1	Kitchen	A large chopping board. Avoid tablecloths and avoid polished glass
Stopwatch	1	Any phone	Count out loud; it is less precise but adequate
Bowl of cold water	1	Kitchen	The sink with the cold tap running
Sticky labels	6	Stationery drawer	A pencil, written lightly on the shell
Notebook	1	Anywhere	Needed to score your predictions honestly
Phone with slow-motion video	1	Pocket	Optional, for counting revolutions

Allergen note: egg. Everything here is food, but the raw eggs carry the usual bacteria, so hands and surfaces get washed afterwards.

Time: prep 20 min including boiling and cooling, experiment 25 min, cleanup 10 min Cost: six eggs Mess level: low, unless you crack one on the counter

Do the Experiment

Step 1 — Boil three eggs properly

Put three eggs in the pan, cover with cold water, bring to the boil, then simmer for a full 11 minutes. Under-boiling is the main cause of a confusing result, because a half-set yolk is still partly liquid. Cool them in cold water for five minutes.

Step 2 — Mix all six and label them by number

Dry the boiled eggs, put them with the three raw ones, and shuffle. Label them 1 to 6 with a pencil or a sticker. Write the numbers in your notebook with blank columns for prediction, test result and the truth.

Step 3 — Run the duration test

Spin each egg on its side on the counter with a flick of the fingers, as hard as you can manage consistently, and time how long until it stops. Do each egg twice and record both times. Do not peek at anyone’s reaction; just write numbers.

Step 4 — Run the stop-and-release test

Spin an egg again. While it is turning, press one fingertip firmly on the top for about a second to stop it completely, then lift your finger straight up and watch for five seconds. Write down whether it stayed still or started to turn again. Do this for all six.

Step 5 — Run the wobble and rise tests

Spin each egg hard and watch the axis. Then take an egg you believe is boiled, lay it on its side, and spin it as fast as you can with two hands, like rolling a pencil between your palms but much faster. Watch what the long axis does.

Step 6 — Commit, then crack

Write your final raw-or-boiled call for every egg before you break anything. Then crack them all into a bowl and fill in the truth column. Count how many you got right with each test separately.

What you should see: boiled eggs spin for 10 to 20 seconds and hold a steady axis. Raw eggs usually stop within 3 to 6 seconds and wobble noticeably while they go. The stop-and-release test is the sharp one: raw eggs creep back into motion almost every time, boiled eggs never do, and most families score six out of six on that test alone. The rise is the showpiece. A boiled egg spun fast enough on its side will tilt and climb until it is spinning upright on its narrow end. Expect to need several attempts, and a raw egg will not do it at all.

What’s Actually Going On

A hard-boiled egg is one solid object. Heat has denatured the proteins in the white and the yolk into a set gel, so when you twist the shell, every bit of the contents turns with it. That makes it a rigid body with a single, fixed moment of inertia, the rotational equivalent of mass, calculated by adding up each piece of mass multiplied by the square of its distance from the spin axis (HyperPhysics on moment of inertia). Once it is spinning, its angular momentum has nowhere to go except slowly into friction at the contact point and into the air, so it keeps going for a long time.

A raw egg is a shell containing two fluids of different density that are free to move relative to it. When you flick the shell, you spin the shell. The white and yolk only come along through viscous drag at the inner surface, which takes seconds to transmit. For most of the spin, the inside is rotating slower than the outside, and the difference is being paid for by shearing a viscous liquid. Shearing a liquid turns rotational kinetic energy into heat (HyperPhysics on rotational kinetic energy). That is why a raw egg stops so quickly: it has a built-in brake that a boiled egg does not have.

The wobble has the same root. A rigid egg has a fixed mass distribution, so its spin axis is stable. A raw egg’s yolk is denser than the white and it migrates as the egg turns, shifting the mass distribution from moment to moment, so the axis cannot settle.

The stop-and-release test is the cleanest because it isolates the mechanism rather than a side effect. When you stop the shell of a raw egg, the liquid inside is still rotating and still carrying angular momentum (HyperPhysics on angular momentum). Let go, and that liquid drags the shell back into motion. A boiled egg has nothing left moving inside it, so nothing restarts it.

The rise is the genuinely hard part of the physics, and it was unresolved for a long time. In 2002, Keith Moffatt and Yutaka Shimomura published an analysis in Nature that set out the problem plainly: a hard-boiled egg spun rapidly on a table with its symmetry axis horizontal will raise that axis to the vertical, and a raw egg spun the same way will not. Both cases lift the centre of gravity, which is what makes it look like a paradox, and their paper derives a first-order differential equation for the inclination of the axis that explains it (Moffatt & Shimomura, 2002). The short version is that slipping friction at the contact point does the work, and that a raw egg cannot exploit it because its interior will not rotate rigidly. It is worth telling a kid that the rise they just produced on the kitchen counter took a Cambridge fluid dynamicist to explain.

How to Explain It to Your Kid

Ages 5–8: One is full of jelly, one is full of soup

Give them two sealed plastic containers, one packed solid with play dough and one half full of water, and let them spin both. The soup one wobbles and stops. Then say the eggs are doing the same thing, and the only difference is that you cannot see inside. Let them sort all six by feel and spin before anybody cracks anything.

Ages 9–12: Inside and outside can turn at different speeds

Ask them to imagine standing still inside a merry-go-round that is turning. The shell can be moving while the stuff inside has not caught up. That lag is why a raw egg is slow, wobbly, and why it restarts when you let it go. This is the age where the stop-and-release test becomes satisfying, because they can state in advance what it should do and why.

Ages 13+: Moment of inertia, dissipation and the rise

Define moment of inertia as the sum of mass times radius squared, and explain that it is only well defined for a rigid body. A raw egg has no single value because the mass can rearrange. From there the whole pattern follows: viscous shear dissipates energy, so the raw egg decelerates; retained angular momentum in the fluid explains the restart; and the rise needs rigid-body coupling to the contact friction, which is why only the boiled one does it. Then read the Moffatt and Shimomura abstract together. It is two sentences and a teenager can follow it.

The question to ask: “If we froze a raw egg solid overnight, how would it spin?” (Like a boiled one, because the contents are now rigid. It should also be able to rise. The question separates “boiled” from “solid inside”, which is the actual variable, and almost nobody gets it on the first try.)

Why Teaching This Early Pays Off

This is the cheapest introduction I know to the idea that you can find out what is inside something without opening it. That is not a minor trick. It is what seismology does to the Earth, what ultrasound does to a body and what engineers do when they tap a casting to hear whether it is cracked. Starting with an egg and a kitchen counter makes the move from “look inside” to “measure a behaviour and infer the inside” concrete and early.

There is a neat process bonus as well. Because you write your prediction for each egg before cracking it, you end up with a hit rate for each test, which is an honest way to compare methods. That prediction-first structure is the Predict–Observe–Explain sequence described by White and Gunstone, and the order matters: a prediction made after the result is not a prediction (White & Gunstone, Probing Understanding, 1992).

On evidence, be careful. Freeman and colleagues’ meta-analysis of 225 studies found active learning outperforms traditional lecturing in undergraduate science and engineering courses (Freeman et al., 2014), and that is good news about active instruction in general. It is a finding about university classes, not about kitchen afternoons, and stretching it would be dishonest. What a Saturday with six eggs can do is make a later abstraction land on a memory. That is enough to justify it.

If the egg theme is working, try our egg drop measured as an impulse problem and the density test for whether an egg is fresh.

Before You Start: What Parents Should Know

Best age	6 to 12. Younger kids can do everything except the boiling, and the rise needs adult-sized hands
Supervision	An adult boils and cools the eggs. Kids can do all the spinning on a table at their own chest height
Real hazards	Boiling water, and bacteria from raw eggs. Wash hands and the counter afterwards. A raw egg spun off the edge of a table is a mess, not a danger
Don’t	Never microwave an egg in its shell to cook it for this. Pressure builds inside and they burst, sometimes seconds after you remove them. Boil them in water, every time

The microwave warning is not hypothetical and it is the only genuine injury risk in this experiment. Shell-on eggs in a microwave can explode, and because the steam is trapped the burst often happens when someone is handling or cutting into the egg. There is no version of this experiment that needs a microwave.

When It Doesn’t Work

The boiled eggs behave like raw ones. You under-boiled them. A yolk that is still soft in the centre is still partly fluid, so it lags and dissipates energy just like a raw one. Eleven minutes at a simmer is the floor for a standard large egg at sea level, and longer at altitude.

Nothing spins for more than two seconds. Your surface is wrong. A tablecloth, a placemat or a wooden board with grain all brake the egg almost immediately. Use a smooth, hard, dry counter. Wipe it first; a damp patch is surprisingly effective at stopping an egg.

The egg will not rise no matter how fast you spin it. Two likely causes. Polished glass is too slippery, so the egg slips instead of gripping, and the rise depends on friction at the contact point. Or you are not spinning it fast enough, which is extremely common. It needs several turns per second, which means a two-handed twist rather than a finger flick.

A raw egg spins for ten seconds. Check its age. An older egg has a thinner, less viscous white and a larger air cell, so it loses less energy to shear. Use eggs from the same box and bought at the same time, which is a fair-test point worth making out loud.

The stop-and-release gives nothing on a raw egg. You either did not get it spinning fast enough to get the liquid moving, or you held it stopped for too long. Hold for about one second. Hold it for five and the fluid inside will have stopped too, and the test has nothing left to detect.

Take It Further With the Spinning Egg Experiment

Build a setting curve. Boil eggs for 2, 4, 6, 8, 10 and 12 minutes, cool them all, then time the spin of each one. Plot boiling time against spin duration. You get a curve that rises and then flattens, and the flat part begins roughly where the yolk has fully set. You have measured protein coagulation with a stopwatch, which is a genuinely good result.

Measure the spin speed and the rise. Film a boiled egg at high frame rate and count how many revolutions it makes in the first half second. Do this for several attempts, noting which ones rose and which did not. There should be a threshold speed below which the rise never happens, and finding it is a real measurement.

Make a viscosity series. Fill three identical sealed plastic capsules or empty plastic eggs with water, cooking oil and honey. Spin each and time it. The thicker liquid shears less at a given speed but dissipates more per unit of shear, and predicting which effect wins before you test it is an excellent argument to have.

What to Watch For Over the Next 3 Months

• Week 4: Your kid uses the spin test on an egg in the fridge without being asked, which is the single best sign the method stuck.
• Month 2: The idea generalises. They shake a wrapped present and reason about what is inside from how it moves, and they say something about liquid versus solid rather than just guessing.
• Month 3: They ask what else you could find out without opening something. Follow it. Tapping a watermelon, hearing a cracked mug, and why a doctor taps your knee are all the same move.

Frequently Asked Questions

Which test is most reliable?

Stop-and-release. Duration and wobble both depend on how hard you spin, how old the egg is and what surface you used, so they give you a judgement call. Stop-and-release gives a yes or no answer that comes directly from the mechanism, and in practice most people get every egg right with it.

Why does a boiled egg stand up on its end?

Because fast spinning plus slipping friction at the contact point pushes its axis from horizontal toward vertical, even though that raises its centre of gravity. Moffatt and Shimomura resolved the apparent paradox in 2002 and noted that a raw egg spun the same way does not rise.

How long do I need to boil the eggs?

At least 11 minutes at a simmer for a standard large egg at sea level. Under-boiled eggs are the main cause of muddled results, so if you are in any doubt, boil one extra and crack it open to check the yolk is set all the way through before you start.

Can we eat the eggs afterwards?

The boiled ones, yes. Spin them, sort them, then peel and eat them. The raw ones should be cooked properly or discarded, and nobody should taste a raw egg. Wash hands and wipe the counter when you are done.

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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. Moffatt, H. K., & Shimomura, Y. (2002). “Classical dynamics: Spinning eggs — a paradox resolved.” Nature, 416(6879), 385–386. https://doi.org/10.1038/416385a
2. Nave, R. “Moment of Inertia.” HyperPhysics, Georgia State University. http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html
3. Nave, R. “Rotational Kinetic Energy.” HyperPhysics, Georgia State University. http://hyperphysics.phy-astr.gsu.edu/hbase/rke.html
4. Nave, R. “Angular Momentum.” HyperPhysics, Georgia State University. http://hyperphysics.phy-astr.gsu.edu/hbase/amom.html
5. Freeman, S., Eddy, S. L., McDonough, M., Smith, M. K., Okoroafor, N., Jordt, H., & Wenderoth, M. P. (2014). “Active learning increases student performance in science, engineering, and mathematics.” PNAS, 111(23), 8410–8415. https://doi.org/10.1073/pnas.1319030111
6. White, R., & Gunstone, R. (1992). Probing Understanding. Falmer Press. (Source of the Predict–Observe–Explain structure used in Steps 3 to 6.)