Soapy math adds some STEAM to playtime

A cube dipped in soapy water emerges with geopanes made of soap film. (Arkansas Democrat-Gazette/Celia Storey)

Trying to sell handwashing as an exciting new childhood hobby? How's that working out?

Activities that highlight soap's eye-popping "secret powers" could help.

Here are projects that also inject some STEAM into soapy time-passing fun — literal steam and also the science-technology-engineering-art-and-math type.


This exploration of surface tension, geometry and shimmering bubbles comes courtesy of Candace Walkington, an associate professor of math at Southern Methodist University's Simmons School of Education and Human Development in Dallas.

Walkington's research examines how to connect abstract mathematical ideas to students' everyday experiences. According to her bio on the SMU website, she conducts research on personalizing math instruction to show students how it applies to out-of-school interests such as sports, music, shopping and video games, and also to their intended careers, like nursing or software design.

She recommends this project for children in grades three to eight.


12 Toothpicks

8 Small poke-able objects that can connect toothpicks, such as raisins, fruit gel snacks, marshmallows, under-ripe blueberries ...

A container deep enough to accommodate a toothpick cube


Dishwashing liquid

Measuring spoons


Optional: paperclip, twist-tie or string to use as a hanger

Make a square with 4 toothpicks and 4 connector objects. Use this square to estimate whether your container is deep and wide enough to easily hold a cube made of toothpicks and enough water to cover the entire cube.

Fill the container with water and squirt in several good squirts of dishwashing soap. Stir. The water must have enough soap to make a film or the experiment won't work. The amount of soap that takes varies by brand. (We used 3 tablespoons of Dawn Ultra to one quart of water. You have plenty of soap if a ring, like the one that holds measuring spoons together, emerges with a coat of film.)

Connect the rest of the toothpicks and small objects to build a cube. Be careful, the cube won't be stable.

Using your hands or a hanger made from something like a paperclip, carefully immerse the cube in the soapy water and lift it slowly out. Observe the shapes created by the soap film.

Save your bubble water to use for cleaning the house or washing dishes.

A cube is a polyhedron — a three-dimensional geometric solid. Try this experiment on other polyhedrons, like pyramids or prisms. Once they are built, dip your shapes into the soapy water and see what complex surfaces — called geopanes — are formed by soap film.

"What happens when these are dipped into the soapy water is amazing!" Walkington says. "You can also integrate science into this activity by talking about surface tension in water and why the geopanes form as they do."

For a downloadable PDF worksheet with more information about geopanes and some ideas for math research they could inspire, click here.

See more of her practical math-teaching activities under "walkSTEM" at the YouTube channel of


Soaps and detergents clean so well in part because they break the surface tension of water. Water's surface tension is strong enough to float surprising things. For instance, a plastic-grid berry basket from the grocery store will float even though the basket is mostly holes.

These simple tricks boil down to fun with surface tension. They are adapted from a book published in 1980, Mr. Wizard's Supermarket Science by Don Herbert.


Clean, cool water

Shallow, light-colored dish

About ½ teaspoon black pepper

Dish soap or bar soap

Pour enough water to fill the shallow dish. Sprinkle the black pepper on the surface of the water. Observe that the particles spread out across the surface. Put one drop of liquid dish soap in the middle OR touch one edge of the bar of soap to the middle of the water.

The soap breaks the water's surface tension. Tension on the rest of the surface remains strong, and it pulls the floating pepper flakes away from the soap.

Wash and dry the dish before using it in other surface-tension experiments.



An old greeting card

Small dish

Dish soap

Cotton swab

A bowl filled with clean, cool water

Use the scissors to cut 1 ½-inch "boats" from the greeting card. To be fancy, cut a slot in the back end of each boat.

Put a few drops of dish soap in the small dish and rub one end of the cotton swab in the soap.

Float the boats on the surface of the water in the bowl. Carefully touch the soapy end of the cotton swab to the slot of each boat and watch as it zips across the water.

What would happen if you tried this experiment in the bathtub?

Does the soap remain on the little boats after they dry? What would happen if you set one of these used boats on the surface of a fresh dish of water sprinkled with pepper?


Because soap breaks water's surface tension, soap film prevents fog on mirrors and windows.

This means that you could write a secret message in the glass that will show up only when it is fogged.

Put three drops of dish soap in a half-cup of water. Dip your finger or one end of a cotton swab in the soapy water and write your message on the window or mirror. After the wet message dries, it won't be obvious until the next time the glass fogs over.

To elaborate on this prank, gather:

A cotton swab

A small amount of soapy water

A hand mirror

A "victim"

It is crucial that you do not gather the victim before you complete all the other steps.

Dip one end of the swab in the soapy water and draw the number 5 on the mirror. Let this dry for several hours or overnight so the 5 becomes invisible.

Now, the trick:

Get your victim. It helps if the victim is old enough to do elementary arithmetic including division. Tell this victim that you have found a magic math mirror that reads minds.

Ask your victim to think of a whole number and write it down where you can't see it.

Next, they must add that number to next larger whole number (the original number plus one, in other words). Then they will add 9 to the result, divide that result by 2 and, finally, subtract the original number. Warn them they must not show you the answer.

You now breathe heavily on the mirror so it fogs, or, if an adult helps you, hold the mirror over the mouth of a teapot that is steaming hot. The answer — 5 — stands out on the glass. It doesn't matter what number your victim started with, the answer is 5.

Think through the series of calculations you had the victim do. Once you see why 5 is bound to be the answer, it's easy to devise another series of calculations that always results in one number.

In this case, if the victim tells you the answer is not 5, the victim needs tutoring in basic math. Another activity!

Style on 05/11/2020