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Elastic Collisions, Gases, and Friction
Name: Evren
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
Hi, Why does friction not apply to gas molecules? My
chemistry books says, "The collision of particles with each other or
the walls of the container are perfectly elastic, no loss of energy
occurs". How is "no loss of energy" possible when gravitation and
friction applies to any matter on earth?
Replies:
To understand the answer to that question, you need to understand
how friction works, and why energy is "lost" to friction when
objects interact. Friction arises because objects are not single
things, but instead are made of many tiny atoms. The bulk kinetic
energy of the atoms all moving in the same direction is partitioned,
in a collision, into the kinetic energy of the individual atoms
moving in many different directions. The kinetic energy is still
there, but as kinetic energy of individual atoms, not as the
"translational" kinetic energy of the large object.
When atoms collide, there are no smaller particles for their kinetic
energy to partition into. (This is not strictly true, but the
nuclei and electrons in the atoms cannot absorb any arbitrary amount
of energy, and in general don't dissipate the small amounts of
kinetic energy involved in room-temperature collisions.)
Richard Barrans
Department of Physics and Astronomy
University of Wyoming
Hi Evren... the difference might be whether the chemistry book is
considering a model (such as an 'ideal' gas), or actual materials. The
statement may be correct if it's describing an assumption that
underpins a model -- or it may just be an oversimplification, or a
plain old error. Before I make any pronouncements about the book being
right or wrong, can you send a little more info? Perhaps a scan of the
page(s) in question, or a citation (if it is on Google books or
something like that)?
Thanks,
Burr Zimmerman
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Update: June 2012
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