The Hidden Physics of “It’s a Small World”! How Circular Motion Creates the Magic [Disneyland Physics]
I’m Ken Kuwako, the Science Trainer. Every day is an experiment!
Smooth, shiny, and almost indistinguishable from real salmon roe. With just a few drops of solution, these beautiful little spheres seem to appear like magic. We recently learned this fascinating experiment during a joint science club event with Kyoritsu Girls’ Junior High School. But these “artificial salmon eggs” are much more than a fun science activity—they beautifully demonstrate one of chemistry’s most fundamental concepts: ionic bonding. Let’s take a closer look at how to make them and discover the science behind their wonderfully bouncy texture.
A Science Club Exchange: A Friendly “Practice Match”
At Chiba University Junior High School attached to the Faculty of Education, our science club regularly takes part in exchange activities with science clubs from other schools. Think of it as a friendly practice match where students share their favorite experiments and learn from one another. This time, we had the opportunity to visit Kyoritsu Girls’ Junior High School, where we came away inspired by many creative activities. Today, I’d like to introduce one of the highlights: making artificial salmon roe.
Gathering the Materials
You’ll need:
1% sodium alginate solution,
10% calcium chloride solution,
acrylic paint,
a 300 mL beaker,
a dropping pipette,
a glass stirring rod,
and a spatula.
Let’s get started!
Here’s the sodium alginate. It comes as a fine white powder.
Place the powder into a small plastic bottle, close the lid tightly, and shake well. Sodium alginate doesn’t dissolve easily, so we kept shaking patiently until the solution became completely uniform.
Next, we added acrylic paint to color the solution. While food coloring is often used, its color may gradually bleed during long-term storage. Acrylic paint stays vibrant much longer, making it a better choice if you’d like to keep your artificial salmon eggs.
Now it’s time to prepare the calcium chloride. Measure out the required amount,
then dissolve it thoroughly in water.
Using a dropping pipette, carefully drip the colored sodium alginate solution into the calcium chloride solution, one drop at a time.
Instantly, each drop transforms into a soft, bouncy artificial salmon egg!
Transfer the finished spheres into a small vial, and you can even take them home. They’re colorful, fun to look at, and make a delightful science souvenir.
Why Does a Single Drop Turn Solid?
Now for the real science.
Why does a liquid drop suddenly become a jelly-like sphere the moment it touches the calcium chloride solution? The answer lies in one of chemistry’s most fascinating mechanisms: the interaction of ions.
Sodium alginate is a natural polysaccharide extracted from brown seaweeds such as kelp and wakame. Each alginate molecule forms a long, chain-like structure covered with many negatively charged sites. In plain water, these long chains float around independently, allowing the solution to remain a liquid.
Everything changes when calcium chloride is added.
As calcium chloride dissolves, it releases calcium ions (Ca²⁺), each carrying a double positive charge. These calcium ions act like tiny molecular bridges, connecting the negatively charged sites on neighboring alginate chains. One calcium ion can link two separate chains together, and millions of these tiny bridges quickly create a three-dimensional network.
As this network spreads, the liquid transforms into a soft gel almost instantly.
Chemists call this arrangement the “egg-box model.” The name comes from the way calcium ions fit snugly into spaces between the alginate chains, much like eggs sitting neatly in the compartments of an egg carton. It’s a wonderfully visual way to imagine what’s happening on the molecular level.
What’s especially interesting is that this reaction begins at the surface of each droplet and rapidly moves inward. The outside gels first, preserving the droplet’s perfectly round shape while the interior solidifies moments later.
That’s the secret behind these glossy, springy little spheres that look so much like real salmon roe.
Contact & Collaboration
Science is full of surprises, and it’s even more exciting when you can experience it yourself! This site is packed with enjoyable science experiments you can try at home, along with easy-to-follow explanations of the science behind them. Feel free to explore!
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