MI collisions

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by north</i>
<br />define collision.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Collision: an encounter between two or more particles that come together or close to each other, and exchange or transfer momentum (energy). This subdivides into elastic and inelastic collisions, where "elastic" means "returns to its original shape after undergoing stress or deformation".

In MM, none of these involve true contact, although apparent contact at any scale where the bodies appear "solid" is the norm. Think of two galaxies colliding as a typical inelastic collision that results in rebound even though constituent stars never make contact. Note also that galaxies look solid if viewed from enough distance that constituent stars cannot be seen. -|Tom|-

Tom,

A point of clarification.

Tom wrote: Collision: an encounter between two or more particles that come together or close to each other, and exchange or transfer momentum (energy). This subdivides into elastic and inelastic collisions, where "elastic" means "returns to its original shape after undergoing stress or deformation".

Is this not only a partial definition. That is "Conservation of momentum" is the difference. In elastic collision momentum is conserved and in inelastic collision some momentum will be lost to heat and other forms of energy re-distribution?

For example even a pool ball (mostly elastic) still results in some heating and isn't truely an elastic reaction.


"Imagination is more important than Knowledge" -- Albert Einstien

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by tvanflandern</i>
<br /><blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by north</i>
<br />define collision.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Collision: an encounter between two or more particles that come together or close to each other, and exchange or transfer momentum (energy).
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give an example for the above.

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This subdivides into elastic and inelastic collisions, where "elastic" means "returns to its original shape after undergoing stress or deformation".

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again give an example.and what if the the striking object(tennis ball)breaks(splits)

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In MM, none of these involve true contact, although apparent contact at any scale where the bodies appear "solid" is the norm. Think of two galaxies colliding as a typical inelastic collision that results in rebound even though constituent stars never make contact.
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can you give an example of this really happening.

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Note also that galaxies look solid if viewed from enough distance that constituent stars cannot be seen. -|Tom|-
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true,are you saying that there is no solid core to a galaxy? i mean that this known?

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Mac</i>
<br />Is this not only a partial definition. That is "conservation of momentum" is the difference. In elastic collision momentum is conserved and in inelastic collision some momentum will be lost to heat and other forms of energy re-distribution?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Yes, and when the whole picture is considered, momentum is always conserved, even for inelastic collisions. The "lost" momentum is simply transferred into increased molecular motions (heat), as you say. -|Tom|-

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by north</i>
<br /><blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">[tvf]: Collision: an encounter between two or more particles that come together or close to each other, and exchange or transfer momentum (energy).<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">give an example for the above.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">??? My fingers colliding with my keyboard? Any two entities in the universe interacting? I have no idea what you are looking for because every interaction is an example.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">[tvf]: This subdivides into elastic and inelastic collisions, where "elastic" means "returns to its original shape after undergoing stress or deformation".<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">again give an example. and what if the the striking object (tennis ball) breaks(splits)<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">You already have your examples. A normal tennis ball has elastic collisions; but if it splits, that is an inelastic collision.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">[tvf]: In MM, none of these involve true contact, although apparent contact at any scale where the bodies appear "solid" is the norm. Think of two galaxies colliding as a typical inelastic collision that results in rebound even though constituent stars never make contact.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">can you give an example of this really happening.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">What was the matter with the colliding galaxies example? Or the tennis ball?

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">[tvf]: Note also that galaxies look solid if viewed from enough distance that constituent stars cannot be seen.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">true, are you saying that there is no solid core to a galaxy? i mean that this known?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">There is no "solid" anything, just objects with higher or lower densities. The high-density ones appear solid if one looks only at the large-scale picture. For example, don't use a microscope, or the illusion of "solid" may vanish. -|Tom|-

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by tvanflandern</i>
<br /><blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Mac</i>
<br />Is this not only a partial definition. That is "conservation of momentum" is the difference. In elastic collision momentum is conserved and in inelastic collision some momentum will be lost to heat and other forms of energy re-distribution?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Yes, and when the whole picture is considered, momentum is always conserved, even for inelastic collisions. The "lost" momentum is simply transferred into increased molecular motions (heat), as you say. -|Tom|-
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I agree. The internal energy is a form of conservation. I didn't mean to imply otherwise but only wanted to clarify that the momentum of macroscopic motion can produce no internal energy change and remain elastic. (That in fact as far as I know can never happen)

Such that there is likely no such thing as an elastic reaction. It is a matter of being less inelastic in nature I would suggest.

"Imagination is more important than Knowledge" -- Albert Einstien