Have you ever been at the lake, pond or even an outdoor pool and watched a bug land on the surface of the water and scurry around without sinking? Did you wonder how that little insect was capable of walking on water? To answer that puzzling question, we found this week’s Saturday Science experiment at Science Friday. Let’s make some water-walking, wire critters!
- Large bowl
- Roll of thin (about 30-gauge), plastic-coated wire
- Sharp scissors or wire cutters
- Paper clips
- Cut a 12-inch piece of plastic-coated wire.
- Bend the wire into a flat shape. This is your critter!
- Fill the large bowl with water. Let rest until the surface is still.
- Gently place your critter horizontally on top of the water. (If it doesn’t stay on the surface the first time, try again.)
- Take your critter out of the water and dry if off.
- Gently place your critter vertically in the water.
- Take your critter out of the water and dry it off.
- Gently bend your critter so that it can hold a paper clip above the water.
- Gently place it back in the water.
- Add a paper clip.
- Repeat until your critter sinks beneath the surface.
When you placed your critter horizontally on top of the water, did it float or sink?
Thanks to surface tension, your water-walking wire critter floated! According to Science Friday, “surface tension is caused by the attraction, or cohesion, of individual molecules to one another in a liquid.” When you gently placed your critter on top of the water, its weight was evenly distributed over an area of water and didn’t break the cohesion between the molecules. That caused your critter to “float” or “walk” on the surface of the water, even when adding additional weight with paper clips. But when you placed your critter vertically in the water, did it float or sink? It sank! This is because a vertical critter takes up a much smaller surface area, so the weight cannot be evenly distributed. When you placed your critter vertically in the water, the cohesion between the molecules broke, and your critter sank straight to the bottom of the bowl.