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Molecular machines
It has recently become possible to
synthesize molecules that function like mechanical devices, such as
switches, motors, brakes, and even small elevators. Such man-made
molecular machines might be considered as nanoscale versions of their
macroscopic analogues. However, many well-known macroscopic concepts no
longer apply at a molecular level. For instance, the concept of viscous
friction becomes meaningless: the friction that a molecular machine
experiences is caused by molecules that have the roughly same size as
the machine, and the time scale of the machine's motion is similar to
that of the molecules causing the friction. Continuum mechanics clearly
cannot be used to describe the dynamics of molecular machines, and new
approaches have to be developed. To obtain a better understanding of
the physics and chemistry of molecular machines, experiments that
directly probe their motion are essential, and the insights obtained
from such experiments should be important for potential applications.
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