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Sound is transmitted from a source to the surrounding air particles, which vibrate or collide and pass the sound energy along to our ears. Without any particles to vibrate we wouldn't hear the sound. How do the air particles stay in the air? Would gravity bring them? And also if air and travel on earth why not in space?

Gravity causes an exponential pressure drop with altitude, effectively keeping a thin "skin" of atmosphere above the Earth.  Some of the atmosphere does escape into space, just not enough to really matter.  The atoms have a temperature, however, meaning the molecules are in motion.  Collisions keep them bouncing all around and don't allow them to all cram into one space (they'd have to lose that motion to all just gather on the ground), so we have an atmosphere.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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