[meteorite-list] Impact Question

From: John Hendry <pict_at_meteoritecentral.com>
Date: Mon, 25 Apr 2011 10:57:08 -0700
Message-ID: <C9DAF040.B9FA%pict_at_pict.co.uk>

In fairness to Sterling I think he did give a simple answer, and I think
you raise a few interesting notions.

I wouldn't get too upset at the nitpicking, it is the mechanism by which
we get closer to the truth, but I can understand how you feel aggrieved by
being pounced on for your simple explanation. Not everyone is cut out for
the diplomatic corps.

I currently believe in the Law of Conservation of Energy. i.e. Energy
cannot be created or destroyed, only converted in form, whether that be
the classical manifestations or to and from matter. So I believe there is
a perfect conversion of the impactor's kinetic energy. A plasma ball is
one obvious manifestation but this patently isn't a perfectly inelastic
collision? All of the kinetic energy is not destroyed. A lot of it will
get transferred to the target body as the crater is excavated and seismic
waves are induced as the earth wobbles. This transferred kinetic energy
will largely be converted to heat quite quickly as the debris lands and
the seismic waves die down, but I bet some remains as the Earth's motion
in space is permanently changed. A small change in velocity but a huge
mass.

So what I find interesting is what the breakdown of energy transfer would
actually be. Patently there is a lot instantly transferred to heat at the
point of contact between impactor and impactee, but how much I wonder is
transferred to non-thermal momentum of and within the impactor, and how
much of that momentum ultimately remains in a different earth motion after
the wobbles die down as they convert to heat?

In addition I should imagine the pressures and temperatures created by
something Chixalub scaled are enormous. Is there any possibility that
matter might be created or destroyed by induced thermonuclear reactions
under such extreme pressure and temperature?

I think your right to nitpick. It should have been called the hydrogen
fusion derived neutron accelerated conventional vanilla flavoured fission
bomb.

Regards,
John




On 25/04/2011 01:44, "Barrett" <BarrettWF at comcast.net> wrote:

>Dear Mr. Sterling K. Webb,
>Simple questions usually dictate a simple answer, which is what I gave,
>and
>is essentially correct.
>Unlike you, I wasn't nit-picking.
>If you want to nit-pick, I can do that also.
>There is no such thing as a perfect conversion when it comes to
>energy/matter conversion, not even with the so-called BIG BANG.
>To nit-pick, your statement:
>" Plasma ball, a certain temperature, a certain energy -- that's the whole
>story, because that's all there is left."
>Is incorrect as it assumes a perfect conversion.
>This simply isn't true in the context of the question he asked. Simple
>evidence that your statement isn't so is the worldwide iridium deposition
>at
>the K/T Boundary is directly attributed to the event cited in the original
>question- "Chixalub impact"
>Our (mankinds) best attempt at nuclear conversion is only a few percent of
>the available fusionable material. Which this is a good thing or the
>somewhat wrongful name for the HYDROGEN BOMB would have eliminated all
>life
>on earth when first tested, as was feared by many. (which would have made
>the original question, my answer and your uncalled-for drival a moot point
>as we wouldn't be here for it)
>
>Your over-reactive reply to my answer is why many people on lists don't
>get
>involved in answering questions.
>For the most part your reply was technically sound and eloquent, but the
>attitude " Let's get our physics straight." I feel was uncalled for,
>offensive and downright nitpicking.
>For his original question, bringing "(Entropy? Don't ask!" is totally
>uncalled for, demeaning and poor usage of () marks as you left the
>closing )
>off. NITPICKING huh?
>ENTROPY as part of your answer IS incorrect as he asked a SIMPLE question,
>not a technical one. I could keep going, but....
>'Nuff said....
>-Barrett
>
>
>
>-----Original Message-----
>From: Sterling K. Webb [mailto:sterling_k_webb at sbcglobal.net]
>Sent: Monday, April 25, 2011 12:28 AM
>To: Barrett; 'Stuart McDaniel'; 'meteorite list'
>Subject: Re: [meteorite-list] Impact Question
>
>Stuart, Barrett, List,
>
>Let's get our physics straight.
>
>The mechanisms being talked about here:
>"burning from entry" and "inertia... travel[ing]
>into the earth" are missing the point. These are
>not "causes," but rather "effects."
>
>All isolated, disconnected bodies have a certain
>amount of energy in them. A small asteroid traveling
>through space has energy that can be described
>in many way depending on what other body you
>reference it to.
>
>All bodies in free motion in a field, like a gravitational
>field, have a potential energy determined by their
>position and their motion. Imagine you are standing
>in your backyard with a nice chunk of rock in your
>hand.
>
>Motionless in your hand, held up by a force from your
>muscles equal to the Earth's gravitational pull, it has
>no kinetic energy at all, because it isn't moving. But it
>does have potential energy. It you were to release it,
>that rock would move under the invisible influence
>of the mysterious gravity field that we all take for
>granted because we've lived in it all our lives. It
>would start to fall...
>
>It would speed up as it fell and acquire an increasing
>amount of kinetic energy, more the faster it went.
>Oddly, its total energy wouldn't change. No, its potential
>energy would decrease as its kinetic energy increased
>because it was getting closer to the center of the
>gravitational field, a position of less potential energy.
>
>And the total energy of the rock, the sum of its potential
>and kinetic energy would be constant, unchanging.
>Dropping rocks is not that exciting, so let's throw that
>rock straight up with all your strength, as high as you
>can toss it.
>
>It's going very fast when it leaves your hand, but as it
>rises and gets further away from the center of the Earth's
>force field of gravity, it goes slower and slower. Its
>potential energy is increasing from its new position at
>the expense of its declining kinetic energy.
>
>Finally, all the energy you gave the rock from your
>muscles will be transformed into potential emery of
>position in the Earth's gravitational field and the rock's
>kinetic energy will be zero -- it will be standing still,
>just for a split second, at the top of your huge toss,
>before...
>
>It starts down, down, gaining speed all the way, as its
>increased potential energy is turned back into kinetic
>energy. Better not let it hit you... But through the entire
>exchange, its total energy hasn't changed, but it has
>been transformed from one kind of energy to another
>and back again.
>
>Enough about little rocks! What about BIG rocks, like
>Chicxulub? Well, the story is the same. If it's going
>about its business and a planet happens to get in its
>way, it will come to a very rapid stop, planets being the
>equivalent of a solid brick wall 8000 miles thick.
>
>Whatever kinetic energy that big rock had, it would be
>transformed into other forms of energy, which would
>act on whatever matter was present and cause another
>transformation of energy, etc., until the vast majority
>of those energies would turn into the Lowest Common
>Denominator of Energy -- Heat.
>
>Heat is just the random motion of everything and
>because of the tendency of entropy to always increase
>everything tends toward the same random motion,
>which we call "temperature." (Entropy? Don't ask!
>I'm only allowed One Mystery per Met-List Post...)
>
>What's odd about kinetic energy is this: it increases
>with the square of the speed, like this:
>
> Energy = Mass x 1/2 x Velocity^2
>
>Double the velocity; four times the energy. Triple it,
>eight times the energy. Ten times the speed, 100
>times the energy...
>
>Let's say I take a tiny pellet like a bullet and throw it
>at you as hard as I can, say, at 35 meters per second,
>you would jump up and yell, "Ouch! What the heck
>did you do that for?"
>
>If you took the same pellet and mounted it in a
>cartridge, put it in a gun and fired it back at me at
>700 meters per second, I wouldn't say much, being
>dead. Twenty times the speed, 400 times the energy.
>
>Now, let's get to that asteroid. Contact velocity with
>the Earth, after its initial speed has been augmented
>by the pull of the Earth's gravity drawing destruction
>down on itself? Let's say 35,000 meters per second
>(a perfectly reasonable figure for a mildly eccentric
>asteroid).
>
>Gram for gram, that big asteroid has 1,000,000 times
>more kinetic energy than the pellet I threw and 2500
>times more kinetic energy than the same pellet you fired
>back as a bullet.
>
>It has more energy per gram than the amount necessary
>to melt it, in fact, many times more than is needed to
>melt the average rock or a chunk or iron, more energy
>than is needed to vaporize rock or the chrome-nickel-steel
>of a meteorite. Energy can't be destroyed, only transformed.
>
>It takes a little over a joule to melt a gram of rock; that's
>the kinetic energy of that gram traveling at the sedate
>velocity of a mere 2100 m/s. A good-sized, high-speed
>impactor would turn to plasma with close to 100%
>efficiency.
>
>And since mass and velocity are the ONLY things that
>matter, it makes no difference at all whether a truly big
>impactor is made of rock or of iron or of pure water ice
>or high-density styrofoam composite or tightly bundled
>goose feathers --- ENERGY is the ONLY thing that will
>determine the outcome, if the energy is above a certain
>rather modest threshold.
>
>We use the same units of measurement to describe
>big impacts as we do nuclear weapons, because both
>consist of the same thing: a super-hot ball of plasma
>on the surface of the planet. All other defining
>characteristics of the event have vanished with a
>single second or two.
>
>Plasma ball, a certain temperature, a certain energy --
>that's the whole story, because that's all there is left.
>The mechanisms that caused it, nuclear reactions or
>kinetic energy, don't matter anymore. Only the
>result... which is the same.
>
>Impacts are, of course more energetic than nuclear
>firecrackers. Chicxulub specs out at 100,000,000
>megatons. The largest thermonuclear weapons, the
>"super-city-busters, like the US B53 9 megaton device
>(no longer in service) are of the range of 5-10 megatons.
>"Ordinary" city-busters, like we would have used on
>Moscow or they on Washington, were 1.0 to 1.5
>megatons, like the B83 1.2 megaton device, the
>largest US thermonuclear device in service today.
>
>You would have to build a pyramid of 80,000,000
>B83 city-busters and light them up all in the same
>instant to create a Chicxulub. I doubt we ever had
>more than a few thousand B83's and the entire
>nuclear arsenal of the world at its peak wouldn't
>have totaled 50,000 megatons, or less than 0.05%
>of a Chicxulub. Kinetic energy is a more dreadful
>and potent power than the clever trick of nuclear
>reactions.
>
>Which is why I find it so strange that some geologists
>dismiss the life-extincting potential of major impacts.
>Me? I think we've been dam lucky.
>
>
>Sterling K. Webb
>
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Received on Mon 25 Apr 2011 01:57:08 PM PDT