spherical oil drop
Fill a glass jar 1/3 full with rubbing alcohol. Carefully
pour in about 1/3 jar of water so that the two liquids mix
as little as possible. One way to do that is to use a funnel
with the small end against the bottom of the glass. But just
pouring the water slowly into the alcohol should do. Fill a
teaspoon with vegetable oil. Tilt the glass. Bring the spoon
to the surface of the alcohol and slowly pour it in. The oil
will form a nearly perfect sphere floating at the center
of the liquid. The denser water sinks to the bottom with
the alcohol floating on top. The oil's density is between
that of water and alcohol. It floats on the water and sinks
in the alcohol and so remains at the boundary of the two
liguids. Gravity pulling down on the oil is balanced by the
bouyancy of the water and alcohol. That allows surface
tension to pull the oil into a sphere.