Chemistry Reference
In-Depth Information
4
S
MART
M
ATERIALS
—
M
ATERIALS
T
HAT
A
DAPT
TO
C
HANGING
C
ONDITIONS
Imagine a peregrine falcon soaring high in the sky. To maintain its alti-
tude, the bird extends its wings to their full 40-inch (100-cm) wingspan,
maximizing the lift . Th en its keen eyes spot a dove fl ying below. Th e falcon
draws in its wings, sweeping them back into a shape resembling a sickle.
A steep dive ensues, known as the “hunting stoop,” in which the peregrine
falcon can reach an astounding speed of 200 miles per hour (320 km/hr).
If the hunt is successful, the falcon smashes into a wing of its target. Th e
dove goes down, and the falcon retrieves its prey.
Unlike the wings of most airplanes, bird wings are not fi xed. Peregrine
falcons change the shape of their wings to suit two diff erent needs—soar-
ing and diving. Th e outstretched wings provide lift , which is excellent for
staying aloft but a bad choice for diving. By sweeping the wings back, per-
egrine falcons plummet to the ground in a fast and controlled dive. Th en,
when the birds want to soar again, the wings can be extended.
Th e wings of peregrine falcons of er an important lesson to chem-
ists and other scientists who develop new materials. Most of the materials
described in the previous chapters involve discovering or designing new
molecular structures to meet a prescribed need. Th ese materials fulfi ll the
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