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Science-y Swimmers

Did you know you can make a paper fish swim? Explore the phenomenon of surface tension in this simple experiment using household materials.

Published April 15, 2020

Surface tension is the way molecules on the surface of water stick tightly together. It's what allows objects like leaves, pine needles and some insects to sit on top of water.

Try filling a glass of water to the brim. If you add more water very slowly, the level of the water will rise above the top of the glass, forming a dome. This is due to surface tension.

You can also break the bond between water molecules—and surface tension—by adding soap to water.

See for yourself by completing a simple experiment using a pan, heavy paper, water and dish detergent or shavings from a bar of soap.


  • Large pan or cookie sheet with sides
  • Heavy paper (card stock or thin cardboard work well)
  • Scissors
  • Water
  • Liquid dish detergent or shavings from a bar of soap


On heavy paper, draw a simple fish or a boat—or your favorite Aquarium animal. (It helps if it has a smooth, pointed shape.) It should be about 2 inches long. Cut it out, then cut out a small rectangular slot in the center of the tail.Science-y Swimmers Step 1 - Cut Out Fish

Fill the pan with a few inches of water.

Science-y Swimmers Step 2 - Add Water

Place your swimmer in the pan.

Science-y Swimmers Step 3 - Add Cutouts

Then, put a soap shaving or drop of detergent in the rectangular slot you cut in the tail and watch it zoom!

Science-y Swimmers Step 4 - Add Soap

If you want to repeat the experiment, you'll need to replace the water in the pan since once the soap is in the water, you have changed the bonds between the water molecules!

If you're looking for creative ways to fill these at-home days, we have some kid-friendly, National Aquarium-approved ideas for crafts and activities that use upcycled and recycled materials. Find more craft ideas and other fun Aquarium activities at

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