Meet Wobbert

Poke it. Now squish harder.

Big, calm and a bit dramatic. Grab it anywhere and pull. Use two fingers to stretch it from two sides. Let go and watch it wobble it out. Tap Tweak (or hover the right edge) to change how soft it is and how fast it calms down.

What it copies from real jelly

Real jelly is a loose net of protein chains holding loads of water. That net does three things, and Wobbert does the same three.

1. It never changes size

Jelly is mostly water, and water won't squash. Squeezing jelly would mean pushing water through pores far too fine to let it out, so the volume stays put however you bend it. The simulation checks this directly: it measures the volume every step, and any change becomes a force pushing the surface back out.

It's the easiest thing to get wrong and the most obvious when it's missing. Let the volume drift and the model slowly deflates into a sad bag, however good it looks.

2. It fights shear, but only just

Sliding one layer past another only stretches the loose chains between junction points, which is easy. Soft jelly is roughly a million times easier to shear than to squash. Here, springs along every edge of the mesh push back, plus a rule that pulls the whole body back towards its resting shape.

3. It loses energy every wobble

Jelly is viscoelastic: part spring, part damper. Without the damper it would wobble forever, and no real jelly does. Each step here throws away a tiny bit of speed, which is what the loss modulus describes in a rheometer (a machine that measures how stuff flows).

What the two sliders do

Slider	Real-world version	What you'll see
Softness	Shear modulus: what the Bloom test measures (softer means lower)	Softer: it slumps more under its own weight and stretches way further before springing back. Firmer: a faster wave and a quicker, tighter wobble.
Internal damping	Loss modulus: energy lost per wobble	Low: it rings on for seconds, like a well-set jelly. High: it settles almost at once, more paste than jelly.

Spot the difference: softness changes how fast it wobbles, damping changes how long. In real jelly they're separate too, which is why scientists who study flow (rheologists) measure both.

The zoom trick

Zoom out and Wobbert looks smaller but wobbles just as fast, because zooming only moves the camera. In real life, size matters: double the jelly and it wobbles about half as fast. A party-sized jelly heaves slowly, a teaspoon of the same mix quivers fast, and the stuff itself hasn't changed. Here's the maths.

What it doesn't do

No surface tension. At this size it would change nothing you could see: for a centimetre-sized jelly, surface tension only competes with elasticity at micrometre sizes. The blobs read explains why.

No tearing. Pull real jelly hard enough and it rips, for good. Wobbert always stretches back, which is handy but not honest. Real jelly has a strain where it fails, and that limit is a big part of what makes something chewy or brittle.

No melting. Gelatin jelly melts in the low 30s °C, below body temperature, which is why it melts on your tongue. Wobbert has no idea what temperature is.

Keep going

Start with what jelly really is to see where the net comes from, or why jelly wobbles for the maths behind the speed.

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