AI Summary
5 min readIn a recent episode of The Rest Is Science, Michael Stevens and Hannah Fry opened a shaken soda can without a geyser by tapping its sides, not its top. This simple trick became the entry point for a wide-ranging conversation about nucleation, mechanical advantage, and the nature of scientific doubt itself.
The Physics of a Nun's Fart
When you shake a carbonated drink, carbon dioxide gas that was dissolved in the liquid collects on microscopic imperfections—nucleation sites—on the can's interior walls. These tiny bubbles cling to the sides and bottom. When you open the can, the sudden pressure drop causes these bubbles to expand rapidly, dragging liquid up with them and creating the familiar foam explosion.
Tapping the sides dislodges those bubbles from the nucleation sites. The freed gas rises to the top of the can, collecting in the headspace. When you open it, only that gas escapes—a gentle release the hosts called "a nun's fart," a phrase Fry claimed was real but their fact-checker disputed. Tapping the top is less effective because it doesn't clean the bubbles off the sides. The only other solution is to wait 10–20 minutes for the gas to redissolve.
The Lever That Can't Move the Earth
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What you'll learn
- 1 (00:00) **Shaken Soda Can Demo** - Michael and Hannah shake a soda can then attempt to open it safely after tapping the sides.
- 2 (04:50) **Why Tapping the Sides Works** - Michael explains the physics of nucleation sites and bubble release.
- 3 (06:30) **The Mechanism of Shaking** - Hannah probes deeper into what shaking physically does to the liquid.
- 4 (08:38) **Pressurized Cans vs. Airplanes** - A brief analogy between can pressure and aircraft fuselage pressurization.
- 5 (13:29) **Listener Question: Losing Faith in Science** - Benjamin asks how to distinguish healthy skepticism from paranoia about the replication crisis.
- 6 (17:55) **The Paywall Problem and Media Distortion** - Michael blames paywalled research for misrepresenting science to the public.
- 7 (19:54) **Science as an Engine of Doubt** - Hannah argues that the core of science is intelligent, positive doubt.
+ Full timestamped outline available in the app
Guests on this episode
Show Notes
A can of fizzy drink has been violently shaken. The pressure is building, the bubbles are ready to erupt, and Michael Stevens is about to open it. But Hannah Fry has a trick up her sleeve. Can a few taps really prevent an explosion?
This week on The Rest Is Science, Hannah and Michael begin with the surprisingly complicated physics of carbonation before tackling a much bigger question: can we really trust science?
From the replication crisis and scientific studies that fail to stand up to scrutiny, to the strange incentives that shape what gets published, they explore why even respected scientific discoveries can turn out to be wrong...and why that might not be such a bad thing.
Along the way, they investigate whether Archimedes really could have moved the Earth with a long enough lever, why aircraft are designed to withstand enormous pressure changes, and what happens when we lose our curiosity.
Plus, an unexpected discussion about nuns, the dangers of absolute certainty, and why asking questions might be one of the most important things we can do.
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