Four supplies - five if your kids are artistic - are all it takes to make artificial fish swim. This was loads of fun, which is my favorite way to teach science concepts.
What You Need
White craft foam
Baking dish of water (either jelly roll or 9- x 13-inch casserole dish)
Liquid dish detergent
What to Do
Cut fish shapes approximately 2 inches long from the white craft foam. Decorate your fish with permanent markers if you want.
Cut a small rectangle out of the tail fin of each fish.
Fill a pan with about an inch of water.
Place your fish in the water, pointed in the direction you want it to swim.
Carefully drop a drip of dish detergent in the fish's tail fin notch.
Watch your fishy zoom forward!
To repeat, you'll need to dump the now soap-filled water and refill with plain water.
Note: We wanted to race two fish but found that it was tough to get the drips of soap in two fish so quickly. As soon as the soap disperses in the water, the fish won't swim.
How Does it Work
The detergent breaks the surface tension of the water, forcing the fish forward as the water molecules break apart because of the soap.
The awesome activity came from a collection of everyday at-home science experiments. I highly recommend Kitchen Science Lab for homeschoolers, supplemental after school science lessons, mad science-themed birthday activities, etc.
Why not teach your kids about fish along with this activity? We read the following books, which inspired the designs of our fish and our REAL understanding of how they swim in the wild.