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Question
What makes a paper clip float?
Asked by: Timothy Hicks
Answer
A paper clip will not 'float' on water in the same sense that a cork will. If you
position
a cork below the surface, it will rise to the surface. A paper clip will not.
If you carefully place the paper clip on the surface of calm water, however, you can keep
it
from sinking because of surface tension. In a liquid, molecules are attracted by
neighboring ones in all directions, except for those at the boundary. The unequal
attraction of neighboring molecules at the surface forms a kind of 'skin'. This surface
tension is responsible for minimizing the surface area of a free-falling drop of water
into
a sphere.
If you look closely at an object suspended by surface tension, whether it is a paper
clip,
insect, leaf, etc. you will notice a slight depression in the surface supporting the
object.
As long as the pressure exerted by an object is low enough, surface tension can support
it.
Low pressure requires a large area in contact with the water relative to weight.
Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor
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