<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no,scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nCan anyone tell if there is data that can tell the speed of an\nautomobile based on the weight of the vehicle and the length of the\nskid marks.\n\nThanks,\nBruce\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Can anyone tell if there is data that can tell the speed of an
automobile based on the weight of the vehicle and the length of the
skid marks.
Thanks,
Bruce
Bastiaan Spanjaard
Jul23-04, 06:34 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no,scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nBruce Anderson wrote:\n> Can anyone tell if there is data that can tell the speed of an\n> automobile based on the weight of the vehicle and the length of the\n> skid marks.\n>\n> Thanks,\n> Bruce\n\nI think you also need some information about the force that the brakes\nexert. If that is in fact the data you meant then I apologize for\nmisunderstanding your post.\nBastiaan.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Bruce Anderson wrote:
> Can anyone tell if there is data that can tell the speed of an
> automobile based on the weight of the vehicle and the length of the
> skid marks.
>
> Thanks,
> Bruce
I think you also need some information about the force that the brakes
exert. If that is in fact the data you meant then I apologize for
misunderstanding your post.
Bastiaan.
Doug Goncz
Jul23-04, 06:34 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no,scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n>From: bwanderson@earthlink.net (Bruce Anderson)\n\n\n\n>Can anyone tell if there is data that can tell the speed of an\n>automobile based on the weight of the vehicle and the length of the\n>skid marks.\n\nActually, since the coefficient of friction on a light car with tires made of\nthe same rubber as the tires on a heavier car or truck is the same for the\ninteraction between the tires on the two vehicles, the relationship between\ninitial speed and skid length is nearly indendent of vehicle weight.\n\nAsk any police officer for more on this. It can get involved but basically the\nskid length is proportional to the vehicle energy, which is proportional to the\nsquare of the vehicle speed. You see energy is also force times distance, and\nthe skidding force stays nearly constant during the skid.\n\nSo:\n\nF * d = 1/2 * m * v^2 or\n\nv = sqrt ( F * d * 2 / m )\n\nBut F is proportional to m so that / m just "factors out".\n\n\nYours,\n\nDoug Goncz ( ftp://users.aol.com/DGoncz/ )\nStudent member SAE for one year.\nLoves in my life:\nDona, Jeff, Kim, Mom, Neelix, Tasha, and Teri, alphabetically.\nSo that is who I spend my time with.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>>From: bwanderson@earthlink.net (Bruce Anderson)
>Can anyone tell if there is data that can tell the speed of an
>automobile based on the weight of the vehicle and the length of the
>skid marks.
Actually, since the coefficient of friction on a light car with tires made of
the same rubber as the tires on a heavier car or truck is the same for the
interaction between the tires on the two vehicles, the relationship between
initial speed and skid length is nearly indendent of vehicle weight.
Ask any police officer for more on this. It can get involved but basically the
skid length is proportional to the vehicle energy, which is proportional to the
square of the vehicle speed. You see energy is also force times distance, and
the skidding force stays nearly constant during the skid.
So:
F * d = 1/2 * m * v^2[/itex] or
[itex]v = \sqrt ( F * d * 2 / m )
But F is proportional to m so that / m just "factors out".
Yours,
Doug Goncz ( ftp://users.aol.com/DGoncz/ )
Student member SAE for one year.
Loves in my life:
Dona, Jeff, Kim, Mom, Neelix, Tasha, and Teri, alphabetically.
So that is who I spend my time with.
Bob Day
Jul23-04, 06:35 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no,scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n"Bruce Anderson" <bwanderson@earthlink.net> wrote in message\nnews:24c50416.0407220922.4b3803f3@posting.google.com...\n>\n> Can anyone tell if there is data that can tell the speed of an\n> automobile based on the weight of the vehicle and the length of the\n> skid marks.\n\nIt\'s going to depend on a whole lot more than that --\nthe type of pavement, the ambient temperature (which will\naffect the pavement ), the internal temperature of the tires,\nthe tire pressure, the design of the tire treads, the material\nthe tires are made of, the weather (dry, rain, snow, ice,\nhumidity, ...), and no doubt a bunch of other things. Beyond\nthat, there may be a whole lot of chaotic variability. I doubt\nyou stand even a fighting chance of determining an anywhere\nnear accurate speed.\n\n-- Bob Day\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Bruce Anderson" <bwanderson@earthlink.net> wrote in message
news:24c50416.0407220922.4b3803f3@posting.google.com...
>
> Can anyone tell if there is data that can tell the speed of an
> automobile based on the weight of the vehicle and the length of the
> skid marks.
It's going to depend on a whole lot more than that --
the type of pavement, the ambient temperature (which will
affect the pavement ), the internal temperature of the tires,
the tire pressure, the design of the tire treads, the material
the tires are made of, the weather (dry, rain, snow, ice,
humidity, ...), and no doubt a bunch of other things. Beyond
that, there may be a whole lot of chaotic variability. I doubt
you stand even a fighting chance of determining an anywhere
near accurate speed.
-- Bob Day
J. J. Lodder
Jul23-04, 08:25 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no,scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nBruce Anderson <bwanderson@earthlink.net> wrote:\n\n> Can anyone tell if there is data that can tell the speed of an\n> automobile based on the weight of the vehicle and the length of the\n> skid marks.\n\n-You- can, to first approximation.\nMass drops out, and deceleration becomes f*g,\n(coefficient of friction times acceleration of gravity)\nIn practice g, since f is nearly 1.\n\nSo\ns = 1/2 10 t^2 = 5 (v/10)^2 = v^2 /20,\nor\nv [m/s] = sqrt(20s[m])\nAn expert will be able to do better,\nbut he will need a lot more information.\nBut even then,\nan expert witness will not be willing to take an oath\non any much greater accuracy without actual experiment.\n\nThe independence of vehicle weight is at first sight surprising,\nand so counterintuitive hat some people simply refuse to believe it.\nSome time ago some students at a police school\ntherefore decided to put it to a test,\nusing empty and loaded 30 ton truck/trailer combinations,\nfor max difference between loaded and empty.\n\nThey were in for an even bigger surprise:\nThey found that in practice the fully loaded trucks\nhad even somewhat -shorter- emergency stops than the empty ones.\nFor practical reasons, such as better road contact,\nless tendency of the wheels to bounce, etc.\n\nBest,\n\nJan\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Bruce Anderson <bwanderson@earthlink.net> wrote:
> Can anyone tell if there is data that can tell the speed of an
> automobile based on the weight of the vehicle and the length of the
> skid marks.
-You- can, to first approximation.
Mass drops out, and deceleration becomes f*g,
(coefficient of friction times acceleration of gravity)
In practice g, since f is nearly 1.
So
s = 1/2 10 t^2 = 5 (v/10)^2 = v^2 /20,
or
v [m/s] = \sqrt(20s[m])
An expert will be able to do better,
but he will need a lot more information.
But even then,
an expert witness will not be willing to take an oath
on any much greater accuracy without actual experiment.
The independence of vehicle weight is at first sight surprising,
and so counterintuitive hat some people simply refuse to believe it.
Some time ago some students at a police school
therefore decided to put it to a test,
using empty and loaded 30 ton truck/trailer combinations,
for max difference between loaded and empty.
They were in for an even bigger surprise:
They found that in practice the fully loaded trucks
had even somewhat -shorter- emergency stops than the empty ones.
For practical reasons, such as better road contact,
less tendency of the wheels to bounce, etc.
Best,
Jan
Cl.Massé
Jul23-04, 03:18 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no,scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n"Bruce Anderson" <bwanderson@earthlink.net> a écrit dans le message de\nnews:24c50416.0407220922.4b3803f3@posting.google.com...\n\n> Can anyone tell if there is data that can tell the speed of an\n> automobile based on the weight of the vehicle and the length of the\n> skid marks.\n\nIt doesn\'t depend on the weight (mass), but strongly on the surface, the\ntyres, and the weather.\n\nThere is a rule of thumb: take the speed in km/h over ten, square it,\nand you have the distance in meters. On wet road, double it.\n\n--\n~~~~ clmasse on free dot F-country\nLiberty, Equality, Profitability.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Bruce Anderson" <bwanderson@earthlink.net> a écrit dans le message de
news:24c50416.0407220922.4b3803f3@posting.google.com...
> Can anyone tell if there is data that can tell the speed of an
> automobile based on the weight of the vehicle and the length of the
> skid marks.
It doesn't depend on the weight (mass), but strongly on the surface, the
tyres, and the weather.
There is a rule of thumb: take the speed in km/h over ten, square it,
and you have the distance in meters. On wet road, double it.
--
~~~~ clmasse on free dot F-country
Liberty, Equality, Profitability.