In physics, the property that causes the
surface of a liquid to behave as if it were
covered with a weak elastic skin; this is why
a needle can float on water. It is caused by
the exposed surface's tendency to contract to
the smallest possible area because of unequal
cohesive forces between molecules at the
surface. Allied phenomena include the
formation of droplets, the concave profile of
a meniscus, and the capillary action by which
water soaks into a sponge.