# Talk:Torsion spring

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## Wrong equation

The differential equation in the section Damped pendulum is incorrect. It is the equation of an ordinary gravity pendulum (Mathieu's equation), not a torsion pendulum. The nonlinear term ${\displaystyle -g\sin \theta }$ only applies to the gravity pendulum, nor should the acceleration of gravity ${\displaystyle g}$ or length ${\displaystyle \ell }$ appear. The correct equation is:

${\displaystyle I{\frac {d^{2}\theta }{dt^{2}}}+\gamma {\frac {d\theta }{dt}}+K\theta =0}$

--Chetvorno 19:41, 16 July 2007 (UTC)

Completely rewrote Damped pendulum and Oscillatory motion of torsion pendulums sections to correct this error and present more useful information. --Chetvorno 19:10, 12 August 2007 (UTC)

## Better terms?

I think the term torsion catapult clock in the 2nd paragraph is not used. I googled the term and didn't find a single reference to it. I think torsion pendulum clock is the term you want. --Chetvorno 20:18, 16 July 2007 (UTC)

## Picture

Is the tortion spring this one? http://www.sterlingspring.com/images/torsion/torsion_spring1.jpg

Yes, those are torsion springs. That would be a great picture to add to the article. Can you get permission to use it? --Chetvorno 23:59, 29 July 2007 (UTC)

## Use in firearms

Best I can tell, the springs inside most firearms to add resistance to the trigger are torsion springs. Can anybody confirm this? Is it worth adding to the article under Uses? --Asriel (talk) 19:46, 2 April 2008 (UTC)

## Error in torsional harmonic oscillators

An IP noted that "there is a mathematical error in at least one of" the equations in this section. I pulled out my vibrations book and found the equation but it's laid out completely different. Moreover, it's been a long time since I've dealt with vibrations, and it isn't coming back quickly. If anyone else has a better source or knowledge it would be appreciated. Wizard191 (talk) 22:35, 16 April 2009 (UTC)

## Wrong Units

If the first equation

${\displaystyle \tau =-\kappa \theta \,}$

has correct units, then the units of ${\displaystyle \kappa }$ must be ${\displaystyle [\kappa ]=N/m}$ because the units of Torque are ${\displaystyle [\tau ]=N/m}$ (so that ${\displaystyle F=R\times \tau }$) and ${\displaystyle \theta }$ has no units. The equation for the energy then is wrong, because it also gives the units ${\displaystyle N/m}$, again because ${\displaystyle \theta }$ or ${\displaystyle \theta ^{2}}$ has no units. Have in mind that Joules are ${\displaystyle [U]=N\times m}$ —Preceding unsigned comment added by Kakila (talkcontribs) 19:28, 30 April 2009 (UTC)

I believe you used the wrong units for torque. Torque is defined as: ${\displaystyle \tau =F\times r}$. So the units of torque are ${\displaystyle [\tau ]=N\,m=kg\,m^{2}\,s^{-2}}$, the same as the units of energy . With this correction, the units in the equations mentioned work out correctly. --ChetvornoTALK 20:39, 30 April 2009 (UTC)

Yes, you are right. A moment of confusion, I guess. Thx

The torque is defined as ${\displaystyle \tau =r\times F}$

=)

## Classical torsion springs don't seem to fit into either of the 'two types' listed.

I'm thinking of the torsion springs used in later Greek and Roman artillery. But I'm sure there are other examples. 71.191.227.176 (talk) 19:25, 27 April 2012 (UTC)

As in a mangonel, you mean, where an arm throws a missile powered by a torsion spring consisting of twisted fibers (ropes)? A similar example is those toy airplanes with propellers powered by a twisted rubber band. I think that would come under the heading of a "torsion fiber". --ChetvornoTALK 20:11, 27 April 2012 (UTC)

## Wrong Link to French Site

The current link to the French language site points to an article about a Torsion Balance. The correct article can be found at this URL: http://fr.wikipedia.org/wiki/Ressort_de_torsion - but I am not smart enough to figure out how to change the link.

Incidentally, the English link on the French page correctly points back to this page. — Preceding unsigned comment added by DazedAndConfused (talkcontribs) 15:42, 27 August 2013 (UTC)

### Entry needs to be split

Can I suggest that the entry labled Torsion_spring#Torsion_balance be split into two distinct entries.

The entry on torsion springs seems to confuse two types of mechanical function: the torsion (rotational resistance and elacticity) and the use of helical springs (which don't use rotational elacticity so much as normal bending resistance, while being wound in a helical spiral)

The torsion balance deserves its own entry. It is one of the most precise experimental tools ever developed, and when grouped with mousetraps, the whole subject is confused. Stewart Fist 01:12, 26 February 2016 (UTC) — Preceding unsigned comment added by Stewart Fist (talkcontribs)

Both types of spring, the helical and the straight, have the same equation, ${\displaystyle \tau =-\kappa \theta \;}$ and both are called "torsion springs" so I think they have to be treated in the same article. The kinematic distinction between the two types which you rightly point out, between bending stresses and torsional stresses, is made in the introduction. Since the torsion fiber belongs in this article, the torsion balance would have to be described here even if it also had a separate article. The differential equation of the torsion balance presented in the section Torsional harmonic oscillators applies to a wider class of mechanical systems than just the torsion balance, such as galvanometers, watch balance wheels and torsion bars, so it would also have to stay. The torsion balance is also described in Cavendish experiment. Given this, my feeling is that a separate article on the torsion balance would be redundant. --ChetvornoTALK 21:17, 26 February 2016 (UTC)

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