How are insects able to move on the surface of a liquid?

How are insects able to move on the surface of a liquid?

Some very small insects can be seen moving with great ease on the surface of water. How are they able to move on the surface of a liquid?

 

Small insects, such as water striders, can move with ease on the surface of water due to the phenomenon of surface tension. Surface tension is the result of cohesive forces between liquid molecules, which create a "film" on the surface of the water, making it difficult for light objects or organisms to penetrate.

 
Explanation:

Surface tension occurs because water molecules are attracted to each other by intermolecular forces, particularly hydrogen bonding. The molecules at the surface of the water are attracted more strongly to the molecules around and below them than to the air above. This creates a surface that behaves like a stretched elastic membrane. Small insects are able to walk on water because their legs do not break this surface tension.

 

Experiment to Demonstrate Surface Tension:

 

Materials Needed:

 ·       A small bowl or container filled with water

·       A small, lightweight needle or paperclip

·       A drop of dish soap

·       A pair of tweezers (optional)

Steps:

1. Prepare the Water Surface: Fill the bowl with water until it's about halfway full.

 

2. Carefully Place the Needle on the Water:

Take the needle and gently place it on the surface of the water using tweezers or your fingers. If done carefully, the needle will float on the surface due to surface tension, despite being denser than water.

 

3. Observation:

Observe how the needle rests on the surface without sinking. This is because the surface tension of the water is strong enough to support the weight of the needle, creating a thin "skin" on which it can float.

 

4. Add Soap and Observe the Change:

Now, add a drop of dish soap to the water near the floating needle.

Observation: The needle will quickly sink to the bottom of the bowl. This happens because the soap reduces the surface tension of the water by disrupting the hydrogen bonds between water molecules.

 

Explanation:

The needle floating on the water's surface is similar to how insects like water striders can walk on water. The insect's legs are coated with tiny hairs that help distribute its weight over a larger area, further increasing its ability to stay on the water’s surface without breaking the surface tension. The soap in the experiment disrupts the surface tension, which shows why the needle sinks when this tension is reduced.

 

Conclusion:

This experiment demonstrates the principle of surface tension, which allows small insects to move on the surface of water without sinking. The cohesive forces at the surface of the water create a strong enough "film" to support the insect's weight, enabling them to "walk" on water.