If you’ve ever looked carefully at a full glass of water or a water droplet, you may have noticed that the water forms a thin, stretchy layer at its surface. This phenomenon is called surface tension. Surface tension is caused by the attraction, or cohesion, of individual molecules to one another in a liquid, especially when they are near repulsive air molecules. Lightweight objects, even ones that do not typically float, may be able to rest on the surface tension of a liquid. This happens when the weight of the object is distributed over a large area so that it doesn’t tear apart the cohesion between molecules. Some insects, such as water striders, are able to stand and travel on the surface of water because of surface tension and spend much of their lives gliding across ponds and streams.

Watch the Science Friday video “Stroke of the Water Strider” (below) to learn about a robot that was inspired by insects’ ability to travel on the surface of water. Follow the directions below to make your own water-walking critter using thin wire, and then test its effectiveness by counting how many paper clips it can carry without sinking.

To make your wire critter:

1. Cut a 12-inch piece of 10-gauge plastics-coated wire.
2. Bend the wire into a unique, flat shape. This will be your water-walking critter.
3. Fill a large, clean bowl with cold water and let it rest until the surface is still.
4. Gently place the wire shape flat on the surface of the water. If it doesn’t stay on the surface the first time, shake off the water and try again.
5. Take your wire out of the water, and place it vertically in the water. What changed? Why?
6. Change the shape of your critter so that it can hold a paperclip above water using surface tension. Try modifying the design to hold as many paperclips on the surface as possible.

Use common sense with scissors and pointy ends of wire. Water may splash in this experiment, so always walk in the laboratory and steer clear of electrical equipment and outlets.