Talk:Young's modulus

"Young Modulus Data Table, inconsistency"

I have added alternative E for Polyethylene terephthalate from its wiki page. I put it in the article so that people would be aware that there is an inconsistency if requiring the information. I do not know what the correct information is. If this page is correct, then the other one will need correcting. If there is a better way to deal with this sort of situation please let me know. my email is greenturtle%ozonline#com*au

The exact material properties of a polymer depend on the distribution of polymer chain length, depending a lot on the production process, eg. the duration, temperature profile and catalysts used of polymerization. Very short polymer chains would result in a liquid or even gass for many common polymers. Volker Siegel (talk) 05:20, 11 October 2016 (UTC)

Derivation of Hooke's law

The section "Force exerted by stretched or compressed material" derives Hooke's law from Young's modulus. This derivation assumes that the change in length (From Young's modulus) is equal to the extension of a spring (From Hooke's law). But the change in length when measuring Young's modulus is usually measured in millimeters, whereas the extension of a small spring can easily be measured in tens of centimeters. What I'm asking is: Are the two terms equal, and is the derivation valid? I plugged in a few numbers (Although I had to guess on the radius of the spring, and the length of the wire in the spring), and the spring constant I got back was a few thousand times larger than the spring constant from a simple F=kx equation. I could have done the calculations wrong, but it's still a large error. There doesn't seem to be any references for the derivation, and I couldn't find any with some googling. (Oops - forgot to sign. - 81.152.176.6 22:33, 15 November 2006 (UTC))

Right, the value of k derived in this case is the spring constant of the wire, not a spring. So you can expect the constant to be much larger for a wire than a spring.--81.152.176.6 15:41, 16 November 2006 (UTC)

The problem is that when a coiled spring is extended or compressed, the wire itself undergoes torsion, not extension.

So Young's modulus is not relevant. This makes the article a bit misleading, perhaps, but not factually incorrect. Hooke's Law is nowadays taken as more general than just applying to coiled springs, so it is reasonable to say that Hooke's Law (for a straight wire or string) can be derived using Young's modulus.

Note also that in a torsion spring the wire is subjected to a bending moment, not torsion!Haruspicator (talk) 23:25, 5 March 2016 (UTC)

References

Table conversions fixes, source units ID needed

A friend earlier today pointed out that the conversion factors in a number of the table entries are wrong. From the bottom, Carbyne is at least correct, but Diamond is not, Graphene is not, Single-walled carbon nanotube roughly is, Osmium roughly is, Tungsten Carbide roughly is, ...

It also is not clear in the table what the source values were in, PSI or GPA. The end result is not just that we're wrong with some math but that we're out of spec with the Wikipedia style guide and best practices.

What we SHOULD do is make sure that the reference tags the source value (i.e., if it was a source in GPA then put the ref in the GPA column with the exact source value, probably put the exact source value in a mini quote note in the ref tag, and then convert that with the units conversion macros in the other column.

Right now, some entries appear to properly have the citation in one units column or another, which presumably validates that that's what the source used, but that should be verified. A lot have the reference in the material column, which doesn't help at all. Someone will definitely have to look at each and every reference to find out what they actually said, and move the ref to the appropriate column.

I am leaving this here to note that I found the issue and that I'm going to start oozing the page towards more correct, but the rate of progress will depend on how fast I can find access to the sources/references. Help appreciated.

Georgewilliamherbert (talk) 04:52, 24 January 2015 (UTC)

Intuition for the units

I wondered for a few minutes about how to intuitively think of the values for Young's Modulus. Eventually I realized that if I apply 75ksi to a piece of teflon and ignore limits on elongation, then it should double in length. If I've understood that correctly, then pointing out that "E = required pressure to double in length" would be helpful in the introduction, "Units" or "Approximate values" sections.

I do not think it belongs to the lead (or Units for that matter). The problem I see is that limits on elongation will in practice always kick in.

It is for instance obvious that stretching and compressing will not be symmetric for those values of stress: one could imagine a material that is still elastic when stretched to double its length (though I have yet to hear of one) but certainly not a material that will remain elastic when compressed to zero length.

If you can find a formulation of that idea that is not misleading or long-winded, I encourage you to be WP:BOLD and add it where you feel it belongs. I would suggest in the "linear vs nonlinear" subsection.

Tigraan (talk) 15:15, 29 January 2015 (UTC)

An elastic band (made of some kind of rubber, whether natural or synthetic) surely? 86.17.152.168 (talk) 08:44, 25 June 2015 (UTC)

Just to be perfectly clear: elasticity (physics) has a precise definition that does not quite match the common language. It is often used by mechanical engineers as synonymous with linear elasticity, just as I did above, although technically it is sloppy language.

For instance, while rubber is more "elastic" than steel in the sense that great deformations will not cause irreversible strains in the material, and more "elastic" in the sense that it is more easily deformed (similar strains cause larger deformations), it is much less "elastic" than steel (for instance) in the sense that the range of deformations where Hooke's law applies is much smaller.

Young's modulus has a meaning only for linear elasticity, so any attempt to use non-linear materials such as rubber to illustrate a point here should be made cautiously. Tigraan (talk) 10:09, 25 June 2015 (UTC)

Aluminum and Rubber examples flesh out

Would be cool if they had numbers and formulae and stuff (I'm sure aluminum's YM is findable in its own article, but still would be fun to see right there). 97.120.108.150 (talk) 20:19, 27 September 2023 (UTC)