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Journalism of Courage
SINDYA N. BHANOO
Keen observers may have noticed that dewdrops form on the tips of grass blades. This appears to be in defiance of gravity: Shouldnt the drops fall toward the bottom?
A study in the American Chemical Society journal Langmuir explains the physics behind this peculiar phenomenon. The author,Martin E R Shanahan,a scientist at the University of Bordeaux in France,suggests that a blade of grass is like a cone,with a narrow top and a wide bottom.
So taking a cone,he modelled the behaviour of two types of dewdrops: a thin film of water and a thicker,spherical drop. In each case,he found that the dewdrop is able to lower its energy state by moving to the pointy tip of the leaf.
Conventionally,we think it should move to the bottom,with gravity, said Thomas Thundat,a nanoscale scientist at the University of Alberta,who was not connected to the study.
In this case,the force that pulls the water toward the smaller radius at the apex of the grass blade,known as the capillary effect,is stronger than the force of gravity, Thundat said.
On flat leaves,however,drops accumulate randomly across the surface.
