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Name: star.girl
Status: student
Age: 16
Location: N/A
Country: N/A
Date: 2000-2001


Question:
Why can insects walk on water?


Replies:
They are so light that they can support themselves by spreading their weight on the surface tension of the water.

J. Elliott


Some insects have a waxy coating on the body and/or feet. The surface tension of this coating [~20 to 30 ergs/cm^2] is much less than water [ 72 ergs/cm^2]. The water then tends to bond to itself rather than "wetting" the bug's feet and unless the bug it too heavy it can remain on top of the water's surface.

Ants, especially carpenter ants, are a good example of such insects. An effective safe insecticide is to surround the base of a house with a surface active agent [surfactant] that adheres to the ants feet. There are a number of non-ionic suitable waxy materials. The surfactant sticks to the ant's feet. The ant returns to the nest and further spreads the surfactant to other workers. When the ants then come into contact with water they will no longer be buoyant and will drown.

You can demonstrate this effect by sprinkling some black pepper on the surface of some pure water in a glass. The pepper floats. Add a drop of liquid dish soap to the surface and the pepper grains will rush away form the soap droplet. Stir gently once or twice and the pepper sinks.

Vince Calder


Hi Stargirl!

It is a property of liquids called surface tension that enables some insects to walk across a liquid surface, usually of a pond or lake.Also a needle can float over the surface of a glass filled with water... Surface tension is a special force that resists to be disrupted by the penetration of a needle (horizontally!) or by a water bug, for example.

These surface forces can be explained by intermolecular forces. A molecule in the center of a liquid is pulled equally in all directions by the molecules surrounding it. But if the molecule is on the surface, it is attracted by molecules at its sides and below it only. There is no corresponding upward attraction. These unequal forces tend to pull inward at the surface of the liquid and cause it to contract. That is why a drop is spherical, for example( to minimize its surface area.)

And thanks for asking NEWTON!

Mabel
(Dr.Mabel Rodrigues)


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