The basic concepts and their explanations
is a very common concept that the bodies heavier than water do not
drown if we put them correctly on the water surface. So the light
metal coin, thin aluminum plates and needles float on the water
surface, although under Archimedes's law they should sink. The free
water surface, as well as the surfaces of some other liquids act
as there is a thin membrane on their surface, that prevents the
bodies to be drowned. That membrane is only on the surface, and
heavier bodies drown according to Archimedes's law.
concepts show that free surface of liquid is in the state of tension.
The presence of that surface tension can be illustrated by the following
experiment. In the circular frame we tie the thread into a loop.
The frame and the loop are drowned into lather. The loop has a very
irregular form in the lather. But, we pierce the bubbles in the
loop, the loop will get the circular form again. So, there is a
force working from inside of the bubble that pulls the thread into
the radial direction.
of the surface is then a consequence of the added energy in the
surface of the liquid due to the forces among molecules. All the
natural processes tend to the state of minimal potential energy
as a stable state, so the free surface of the liquid tends to take
over a minimal surface consistent to the conditions of the work
of the outer forces and pot sides' borders. The smallest surface
for the given volume has the sphere; so every free liquid that is
influenced by the work of the outer forces and that is not limited
by the pot would get the form of the sphere. On the Earth water
and other liquids disperse into drops, which are a little bit elongated
due to work of gravitation and other forces.
The rigid body
If we drown
a thin tube into a liquid, the liquid in tube will raise or fall.
If we drown a tube into water, the liquid will raise; if drown it
into mercury the liquid will fall. That concept is called capillarity.
The capillarity is explained by the tension of the surface.