[meteorite-list] Impact Question
From: John Hendry <pict_at_meteoritecentral.com>
Date: Mon, 25 Apr 2011 10:56:13 -0700 Message-ID: <C9DAE248.B982%pict_at_pict.co.uk> Sterling, On 24/04/2011 23:28, "Sterling K. Webb" <sterling_k_webb at sbcglobal.net> wrote: <snip> >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. <snip> I followed all but the above? Assuming physical properties for say pure iron? Specific Heat Capacity for iron = 460 J/kg/degK (http://www.engineeringtoolbox.com/specific-heat-metals-d_152.html) Melting point of iron = 1530 deg Celcius = 1803 Kelvin (http://www.muggyweld.com/melting.html) Assuming incoming temperature of impactor is 200 Kelvin (http://en.wikipedia.org/wiki/Asteroid_belt) Then to raise the 1 gram impactor to its melting point requires a temperature increase of 1603 K and the energy required to do this should be roughly this? 1603 x 0.001 x 460 = 737 Joules. So a typical value would be more like one *Kilojoule* to melt a gram of meteorite if I have my sums right (stone would be higher, maybe around twice as much as iron) Considered as kinetic energy, 1000 Joules would represent a velocity of sqrt[1000/(0.5*0.001)] = 1414 m/s which is ballpark consistent with your velocity estimate, but the energy you quote is a tad on the light side is it not? Regards, John Received on Mon 25 Apr 2011 01:56:13 PM PDT |
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