[TheForge] Rebound and Work

[Steve Smith]

Well, we're confused here. I started out thinking (and still think) that 
if the hammer rebounds, you've applied more force to the work than if 
the hammer stops dead. My wife and I discussed this for awhile and came 
to the conclusion that our heads hurt.

Steve

Jonathan Nedbor wrote:
> Mike,
> I remember seeing some old advertising for some brand of cast anvil that 
> addressed the rebound issue. Their copy stressed that the cast anvil 
> with minimum rebound allowed for more of the force from the hammer blow 
> to penetrate the metal being worked on, thusly producing more "work". 
> They contrasted this with a forged anvil with good rebound and claimed 
> their cast anvil, for this reason was far superior.
> 
> Food for thought or just plain old advertising sleight of hand? If you 
> can convince 'em, confuse 'em.
> 
> Jonathan
> 
> 
> ----- Original Message ----- From: <theforge-request at mailman.qth.net>
> To: <theforge at mailman.qth.net>
> Sent: Saturday, November 05, 2005 4:01 AM
> Subject: TheForge Digest, Vol 22, Issue 14
> 
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>> Today's Topics:
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>>   1. Re: uri hammer (Mike Spencer)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Sat, 5 Nov 2005 00:46:34 -0400
>> From: mspencer at tallships.ca (Mike Spencer)
>> Subject: [TheForge] Re: uri hammer
>> To: theforge at mailman.qth.net
>> Message-ID: <200511050446.jA54kYs13470 at bogus.nodomain.nowhere>
>>
>>
>>> Hmm.  Looking at the web page, I wonder if you ever figured
>>> out the energy imparted to the hot iron by the hammer head?
>>
>>
>> Well, I have a little trouble with the computations. [1]  But as a
>> first approximation, the kinetic energy of the hammer head is:
>>
>>    1/2 X mass-of-hammer X velocity-of-hammer X velocity-of-hammer
>>
>>    1/2 m v^2
>>
>> If the hammer head stops dead with no rebound, then there's zero
>> kinetic energy so all the kinetic energy of the hammer must have been
>> converted into work in deforming the the iron and is eventually
>> dissipated internally as heat.  If there's rebound, that kinetic energy
>> has to be subtracted from the original KE to get how much went into
>> the iron.
>>
>> Rebound is hard to measure with a hand hammer.  And the above ignores
>> all the other possible variables such as energy absorbed by the anvil
>> and stump/stand, energy dissipated as sound, etc.
>>
>> Those pics on the web page were done with hot iron.  We did some
>> others with a piece of lead and with a piece of cold steel at faster
>> frame rate.  I haven't gone over those carefully but intuitively,
>> there was less rebound with the lead and, of course, a great deal with
>> cold iron.
>>
>> Thinking about this stuff is for the winter when the shop is cold, the
>> snow deep and the house warm.  Maybe this winter.  I finally found
>> some manuals for Maple V and mean to play with it when the weather is
>> nasty.
>>
>>
>> - Mike
>>
>> [1] "...a little trouble with the computations."  Tedious and OT.  I
>>    don't have trouble with the usual, textbook, frictionless billiard
>>    ball or ballistic pendulum examples of conservation of momentum.
>>    But in the case of hammering on an anvil, I can't quite figure out
>>    how to do the computations when the "system" consists (1) a hammer
>>    of mass m and velocity v colliding with (2) the earth of mass
>>    5.9736e24 kg and velocity 0, of which latter a little piece (the
>>    hot iron) is (almost) completely inelastic.  I need to put my feet
>>    up, read some hard stuff (hard for me, anyhow) and scribble,
>>    scribble, scribble.
>>
>> -- 
>> Michael Spencer                  Nova Scotia, Canada       .~.
>>                                                           /V\
>> mspencer at tallships.ca                                     /( )\
>> http://home.tallships.ca/mspencer/                        ^^-^^
>>
>> -- 
>>
>>
>>
>>
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>> End of TheForge Digest, Vol 22, Issue 14
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