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” 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.
Target Grades: Grades 6-8
Content Areas: Physical Science
Activity Types: Lab Investigation, Design Challenge
Time Required: 20 minutes
The Stroke of The Water Strider
- Large bowl of cold water
- Roll of thin, plastic-coated wire, about 30-guage
(available at most hobby and electronic stores, and online here
- Sharp scissors or wire cutters
- Paper clips
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.