Why You Can Run on Oobleck: Non-Newtonian Fluids Explained (2026)

Mix cornstarch and water in a bowl and you get something that should not exist. Stir it slowly and it pours like thick cream. Slap it and it slaps back, hard as a tabletop. Squeeze a handful and it becomes a dry, crumbly ball, then melts through your fingers the moment you relax your grip. People have run across swimming pools filled with the stuff, and sunk to their knees the moment they stopped.

The short answer: oobleck is a dense suspension of tiny starch grains in water. At rest, a thin film of water keeps the grains apart and lets them slide past one another. Hit it fast, and the grains are shoved into direct contact faster than the water can get out of the way. They lock together by friction into a temporary solid that can push back with enormous force, then relax into liquid again a moment later. Physicists call this shear thickening, and the details took more than half a century of argument to pin down. A new study published in April 2026 shows the goo still has surprises left.

Where the name comes from

The name comes from Dr. Seuss. In Bartholomew and the Oobleck, published in 1949, a bored king of the Kingdom of Didd orders his magicians to make something new fall from the sky. They deliver a sticky green goo that gums up the whole kingdom until the page boy Bartholomew Cubbins persuades the king to apologize. The book won a Caldecott Honor in 1950 (ALA), and generations of science teachers borrowed the name for the cornstarch-and-water mixture that behaves just as strangely.

To scientists, oobleck is a non-Newtonian fluid. Isaac Newton’s simple rule for liquids says a fluid’s thickness, its viscosity, stays the same however hard or fast you push it. Water, alcohol and most oils behave that way. Plenty of everyday substances don’t. Ketchup and paint get runnier when you shake or stir them, which is called shear thinning. Oobleck does the opposite. Its resistance rises as you push harder, which is called shear thickening, or dilatancy (Wikipedia).

Why it turns solid when you hit it

For decades, the standard explanation leaned on the water. When the grains are pushed together quickly, the thinking went, the water squeezed between them generates so much drag that the mixture briefly clumps into "hydroclusters" that resist flow. That idea was not wrong, exactly, but it could not account for how strong oobleck gets. The drag forces it predicted were far too weak to hold up a running person.

Friction, not just drag

The picture that took over in the 2010s puts friction at the center. In a 2013 paper in Physical Review Letters, Ryohei Seto, Romain Mari, Jeffrey Morris and Morton Denn at the City College of New York simulated hard particles in liquid and added one rule: when two grains come close enough, the water film between them fails, and they touch and grind like grains of sand. With that rule in place, the simulation finally reproduced the sudden jump in viscosity seen in real cornstarch. When they turned friction off, the shear thickening disappeared completely (Physics).

The physicist Eric Brown, writing about that work, compared a shear-thickened suspension to a pile of blocks stacked from the bottom of a swimming pool to the surface. If the blocks reach all the way down, you can walk across them. If they are only floating, you sink. In oobleck, a hard push builds those load-bearing chains of touching grains in an instant. Let go, and the chains fall apart.

A jamming front that grows under your foot

Shear alone still could not explain the running trick. Scott Waitukaitis and Heinrich Jaeger at the University of Chicago tackled that directly. In a study published in Nature in July 2012, they fired a metal rod into a tank of cornstarch suspension and watched with high-speed cameras, embedded force sensors and X-ray imaging (Nature).

What they saw was a solid that grew. The impact compressed the grains directly under the rod, jamming them together, and that jammed region pushed into the liquid in front of it, jamming that too, like a snowplow building a wall of packed snow. The stresses it generated were about 100 times larger than anything measured when the same mixture was merely sheared. "It essentially grows its own solid as it propagates," Jaeger told UChicago News (University of Chicago).

If you were to punch the suspension, you might break your wrist. (Scott Waitukaitis, University of Chicago, to Science News, July 2012)

That is why a runner stays on top. Each footstrike drives a jammed column down into the pool, and the column carries the runner’s weight for the fraction of a second the foot is planted. Stand still, and the grains slowly unjam, the water flows back between them, and down you go.

The 2026 twist: drops that splash before they stiffen

You would expect a flying blob of oobleck to behave one of two ways when it hits a surface. A watery mix should splash like a raindrop. A thick mix should stiffen on impact and land like a pellet. In a paper published on April 7, 2026, in Physical Review Letters, Anahita Mobaseri, Xiang Cheng and colleagues at the University of Minnesota, Northwestern University and the University of Santiago, Chile, filmed drops of cornstarch and water hitting a force sensor at high speed and found a third behavior (Physics).

Dilute mixtures did splash like ordinary liquids, and concentrated ones did firm up. But the densest drops, hitting fast enough, briefly spread out like a liquid first and only turned solid a moment later, as the flow slowed. The explanation is a race between the drop’s momentum and dilatancy, the need for packed grains to spread apart before they can move. At the very start of a fast impact, the drop’s inertia wins. The team built a single model that describes all three behaviors (Physical Review Letters). As Physics magazine noted, the findings could help engineers control thick, particle-laden fluids in 3D printing and industrial coating.

Other 2026 work keeps finding new wrinkles. A study published in March 2026 in the Journal of Fluid Mechanics sheared cornstarch under a layer of silicone oil and found that a soft boundary lets slow-moving density waves and long-lived clusters form, while a stiffer one produces sudden, system-spanning jams (Journal of Fluid Mechanics).

How to make oobleck at home

The recipe is about as simple as kitchen science gets, and it is a reliable crowd-pleaser with kids.

Mix it. Start with roughly one part water to one and a quarter parts cornstarch, the ratio often quoted for a good shear-thickening mix. Add the water slowly and stir by hand. If a quick tap with a spoon cracks the surface but a slowly lowered finger sinks in, you have it right.

Tune it. Too runny and nothing happens when you slap it, so add cornstarch a spoonful at a time. Too stiff and it crumbles like wet chalk, so add a splash of water. A few drops of food coloring help kids see it flow.

Test it. Squeeze a handful into a ball, then open your hand. Punch the surface, then rest your fist on it and feel it sink. Drag a spoon through it slowly, then yank it fast. Each test shows the same rule: speed and force make it solid.

Throw it out properly. Don’t pour oobleck down the sink, because the starch can settle and clog the drain. Let it dry out in the bowl or on a tray, then scrape it into the trash.

If you have an old subwoofer you don’t mind getting messy, you can push further. Lay a thin film of plastic over the speaker cone, pour on a puddle of oobleck and play a low tone. The vibration repeatedly thickens and relaxes the mixture, and it rises into wriggling fingers and tendrils, sometimes called oobleck monsters.

Oobleck’s cousins: wet sand, quicksand and ketchup

Wet sand. Walk along a damp beach and the sand around each footprint briefly goes pale and dry. That is dilatancy in action: your weight shears the packed grains, they have to spread apart to move, and the gaps between them pull water away from the surface (Wikipedia).

Quicksand. Quicksand is a different beast, and much of its movie reputation is wrong. In a 2005 study in Nature, Daniel Bonn and colleagues found that their quicksand, a mix of sand, clay and salt water, is extremely sensitive to stress: a 1% change in force made its viscosity drop by a factor of nearly a million. Struggling turns it to liquid, then the sand quickly settles into a dense sediment around your legs. Pulling a foot out at one centimeter per second would take about the force needed to lift a medium-sized car. But a test object with roughly the density of a human body sank only about halfway. "Although you are trapped, you cannot drown," Bonn told Science, advising anyone stuck to lift a foot very slowly and twist the leg so water can seep down around it (Science).

Ketchup, paint and toothpaste. These are oobleck’s opposites. They are shear thinning, so they get runnier the harder you shake, squeeze or brush them. That is why a stubborn ketchup bottle suddenly floods your fries after a few hard thumps.

Ordinary water has strange tricks of its own when conditions get extreme, such as the Leidenfrost effect, which lets droplets skate across a very hot pan on a cushion of their own vapor. Oobleck just needs a box of starch.

Where shear thickening is put to work

Liquid body armor. In the early 2000s, Norman Wagner at the University of Delaware and Eric Wetzel at the U.S. Army Research Laboratory developed a shear-thickening fluid of hard silica nanoparticles in polyethylene glycol and soaked Kevlar fabric in it. In a 2004 demonstration, an ice pick went straight through four layers of plain Kevlar but was stopped by four layers of treated fabric, which stays flexible until something hits it fast (University of Delaware). Their patent on armor using shear-thickening fluids was granted in 2009 (Google Patents).

Impact padding. Materials sold under names like D3O use the same principle in motorcycle armor, sports pads, work gear and cases for electronics: soft and bendy in normal use, stiff the instant they take a hit.

Pothole patches. In 2012, a team of Case Western Reserve University undergraduates won first prize in a materials contest sponsored by Saint-Gobain for a pothole patch: a tough, waterproof bag of shear-thickening fluid that slumps to fill the hole, then stiffens to carry a car tire as it rolls over (Popular Science).

Cars. Some all-wheel-drive systems use a viscous coupling filled with a thickening fluid. When the front and rear wheels turn at the same speed, little happens. When one pair starts to slip, the shear rises, the fluid thickens and more power flows to the wheels that still have grip (Wikipedia).

Shear thickening can also be a nuisance. In factories that pump dense slurries, inks or concrete, a mixture that jams unexpectedly can stall pumps or damage mixer blades, which is one reason physicists are still working so hard to predict exactly when it will happen.

The bottom line

Oobleck looks like a toy, but it sits on a real frontier of physics. Its grains act like a liquid when they have time to slide on films of water, and like a solid when they are forced into frictional contact faster than the water can escape. That one idea explains the punch that bounces off, the runner who stays dry and the vest that stops an ice pick, and the 2026 splash experiments show that how fast you push still matters in ways nobody predicted. All of it is waiting in a box of cornstarch in your kitchen cupboard.

Related on aglena: Ferrofluid Spikes Explained: Why Magnetic Liquid Forms a Hedgehog (2026), The Coin That Screams Toward Infinity: The Strange Physics of Euler’s Disk

Further reading