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Jal
01-29-2007, 06:42 PM
Does anyone have a copy of this article or is willing to provide a summary of the conclusions:

http://www.iop.org/EJ/article/0022-3727/4/1/421/jdv4i1p160.pdf

Jim

Bob_Jewett
01-30-2007, 10:25 AM
<blockquote><font class="small">Quote Jal:</font><hr> Does anyone have a copy of this article or is willing to provide a summary of the conclusions:


http://www.iop.org/EJ/article/0022-3727/4/1/421/jdv4i1p160.pdf
(http://www.iop.org/EJ/article/0022-3727/4/1/421/jdv4i1p160.pdf)

Jim <hr /></blockquote>
The experiment was to have 5-cm metal spheres collide and measure the velocity and contact time electronically. The results were that Hertz' Law seems to fit OK, and the actual contact times were around 200usec, similar to billiard ball contact times. Two different metals were used, with one of them quite lossy, but Hertz was still valid.

Jal
01-30-2007, 12:17 PM
Thanks Bob.

I have an old oscilloscope and was thinking of doing it myself, using a thin conductive coating. Much easier though to obtain someone else's results. I do wish that they had used standard balls.

Jim

cushioncrawler
01-31-2007, 12:50 AM
Jim. I dont agree with Bob here. In the few articles that i have come across, where fellows have measured impacts, a comparison with Hertz haz allwayz shown that Hertz is allways less than 50% of measured, or more than 200% of measured. He should have stuck to car (and truck) rental. Actually he helped me to shift my 12' table a few weeks ago -- but other than that, he aint much value at all i reckon.

Of more interest than impact time, i reckon, is "e". It appears that most metals suffer lots of non-elastic deformation, even for slowish impacts, and this of course affects "e", and impact time allso. I have lots of stuff on this. Seems that aluminium is about the worst metal for "e". Riso Levi couldnt believe the narrow loozer angle, much narrower than for ivory balls even. Must be koz (olden days) aluminium is very crystalline. Golfers like a driver that has been annealed or tempered or something so that the face is amorphous (is that the word?? Hal will know), ie non-crystalline.

I might even have the article u are looking for -- I will have a look, will send u a PM if i find it. madMac.

Jal
01-31-2007, 03:20 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Jim. I dont agree with Bob here. In the few articles that i have come across, where fellows have measured impacts, a comparison with Hertz haz allwayz shown that Hertz is allways less than 50% of measured, or more than 200% of measured. He should have stuck to car (and truck) rental. Actually he helped me to shift my 12' table a few weeks ago -- but other than that, he aint much value at all i reckon.<hr /></blockquote>Hi Mac,

The only two articles I've read on it indicate that his law holds pretty well for inelastic collisions as well as elastic, even though he derived it for elastic ones. Besides the article I asked about, another one is here (http://www.oxfordcroquet.com/tech/gugan/index.asp), which I think Bob pointed out some time ago. Since I'm not familiar with Hertz's derivation, it would be hard to decide whose tests are right, the ones that support it or the ones that don't.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Of more interest than impact time, i reckon, is "e". It appears that most metals suffer lots of non-elastic deformation, even for slowish impacts, and this of course affects "e", and impact time allso. I have lots of stuff on this. Seems that aluminium is about the worst metal for "e". Riso Levi couldnt believe the narrow loozer angle, much narrower than for ivory balls even. Must be koz (olden days) aluminium is very crystalline. Golfers like a driver that has been annealed or tempered or something so that the face is amorphous (is that the word?? Hal will know), ie non-crystalline.<hr /></blockquote>My interest is just in knowing the contact time at particular speeds (or one speed and using Hertz's law to obtain it at others.) I have no reason to doubt Wayland Marlow's results, but I don't know at what speed his .0002 sec(or .00022?) applies. Do you have any info on this?

<blockquote><font class="small">Quote cushioncrawler:</font><hr>I might even have the article u are looking for -- I will have a look, will send u a PM if i find it. madMac. <hr /></blockquote>Thanks Mac, but someone already sent one along.

Jim

cushioncrawler
01-31-2007, 03:46 PM
<blockquote><font class="small">Quote Jal:</font><hr> ....My interest is just in knowing the contact time at particular speeds (or one speed and using Hertz's law to obtain it at others.) I have no reason to doubt Wayland Marlow's results, but I don't know at what speed his .0002 sec(or .00022?) applies. Do you have any info on this?.... <hr /></blockquote> Jim -- I aint got Marlow -- iwillhavtagetacopyoneday off Bob. madMac.