SURFACETENSION

SURFACETENSION

What’s going onat the surfaceof a liquid?

What’s going onat the surfaceof a liquid?

Let’s takea look!

Particles that make up a liquid are in constant random motion; they are randomly arranged.

You might expect the particles at the surface,at the micro level, to form a random surface,as shown below.

You might expect the particles at the surface,at the micro level, to form a random surface,as shown below.

= intermolecularattractions

But how do intermolecular forcesinfluence the surface?

Under the surface, intermolecular attractions pull onindividual molecules in all directions

= intermolecularattractions

= intermolecularattractions

= intermolecularattractions

At the surface, pull on the molecules is laterally and downward;there is negligible intermolecular attractionsabove the molecules (from the medium above, such as air).SO, the net force on surface molecules is downward.

The result of this downward force is thatsurface particles are pulled down untilcounter-balanced by the compressionresistance of the liquid:

Surface molecules are compressedmore tightly together,forming a sort of skin on the surface,with less distance between themcompared to the molecules below.

Surface molecules also form a much smoother surface thanone would expect from randomlymoving molecules.

This explains the characteristic roundedshape that liquids form when droppingthrough the air: The molecules are all being pulled toward the center.

This explains the characteristic roundedshape that liquids form when droppingthrough the air: The molecules are all being pulled toward the center.

Water in particularhas a very highsurface tension. What property doeswater have that wouldgive it such a strongsurface tension?

This is the water strider insect. Have you seen one?

How is this possible?