Talk:Jerk (physics)

Full wording for m/s³

I would like to add something about 'metres per second per second', or 'm/s/s', but I am unable to think of a good location in the article to place this. I think this would be a useful addition for those like myself that only have an education in physics up to high-school level, where the full wording is more intuitive than m/s³. 94.173.75.170 (talk) 12:01, 21 October 2023 (UTC)[reply]

Definition

http://www.wordorigins.org/wordorj.htm states:

Do you want to know who a jerk is?! My english teacher!!!!!! I mean seriously, he LOVES to pick on me and my friends. GRRRR!!!!!! I HATE HIM!!!!! Jerk is an old word, dating to the sixteenth century. The word echoes the sound made by a short, sharp movement. The word is unremarkable, except that it has several modern, slang usages that are interesting.

A soda jerk is someone who makes a living by jerking, or pulling, sodas at a lunch counter, the name coming from the jerking motion required to open a tap.
To jerk off is to masturbate, again coming from the motion required for men to engage in this activity. Founded by a Mr. Jerk Gosling in 1623.
A jerkwater train was originally a small locomotive that serviced branch lines. Its small boiler requiring frequent filling by train crews which would have to dismount, form a bucket brigade, and jerk water from a river to feed the steam engine. The term dates to the 1870s and is American in origin. The term jerkwater town eventually came to mean any rustic or backwards town, along a train line or not.
Finally, the most common usage of jerk, meaning a fool or inept person, probably derives from jerkwater. A jerk being a resident of a jerkwater town. This usage dates to the 1930s.
The term jerky, meaning dried and preserved meat has a different origin. That is a corruption of the Peruvian Spanish charque, meaning (what else?) dried and preserved meat.

I didn't have time to modify the article. I would like to point out that while "jerk" often implies stupidity or incompetence, that is usually not the most common usage. The most common one, as I've heard, refers to someone who frequently behaves in a manner inconsiderate of other people (on a local scale, as in "That jerk cut me off," or on a global scale, as in "Chicks dig jerks").

23:22pm EST 2004 March 21

Would you please add references that give more information about the Jerk.

I added the English-language slang meaning of Jerk. If this qualifies as a dicdef and therefore does not belong, remove it.

It does and I did.—Herbee 06:40, 2004 Mar 17 (UTC)

I believe I'm correct in saying that the origin of the term is unclear but may have come from one of those two derivations. If I am not, and there is someone who knows its correct origin, please post it. Mike Church 10:02, 14 Mar 2004 (UTC)

This seems to be legitimate - I was soo ready to delete it :). [1]

Yes in engineering school we were taught that jerk was the derivative of acceleration, an apropos name. However, c.f. the other physics use of jerk^{[failed verification]} Poppafuze 05:59, 6 November 2006 (UTC)[reply]

Fourth derivative

There are some terms for the fourth derivative here, but the article is missing the only one that I've heard before, "twitch". Has anyone else ever heard this term in reference to the fourth derivative of displacement? --Monguin61 05:46, 20 December 2005 (UTC)[reply]

Humph ! Why is this page locked ? Please add a link to the general page for this kind of word ! Derivatives of position Should it be in the Phsics Project ? That page even has its Talk page locked !

I've heard of "twitch" before, and I think it was in the context of the 5th derivative, and I swear I read this somewhere on Wikipedia. Also, it spoke of the unofficial name of another derivative (6th?), being "impulse". I can't find this anymore either. — Preceding unsigned comment added by Zom-B (talk • contribs) 21:51, 17 December 2022 (UTC)[reply]

--195.137.93.171 13:00, 20 August 2007 (UTC)[reply]

Infinite jerk

Isn't it impossible to accelerate instantaneously? Motion is an infinitely differentiable entity; there is no such thing as an infinite jerk, just a very very high jerk.

Yes, that's true. Infinite jerk over an instant of time is an idealization, just like infinite force over an instant of time is sometimes used to characterize an elastic collision between two objects. PAR 19:24, 12 January 2006 (UTC)[reply]

The right answer is double: 1) physically it is possible to accelerate instantaneously, given that the definition of "instantaneously" means in fact "faster than the precision of the measure" 2) mathematically infinity is avoided by using a Dirac distribution ; in that case you must use distributions (in the sense of Laurent Schwartz) instead of functions and then you avoid the "infinite jerk" nonsense —Preceding unsigned comment added by 217.154.243.205 (talk) 14:59, 12 August 2010 (UTC)[reply]

I added some information about discontinous acceleration and therefore unbounded jerk in several idealized situations, even mentioning the Dirac-Delta. Purgy (talk) 11:07, 7 August 2014 (UTC)[reply]

tongue in cheek

"with some nonzero positive value for tongue-in-cheek" - very clever, I rate that! --LeakeyJee 07:28, 4 May 2006 (UTC)[reply]

Original research

Where did all this relativistic, mass-changing-with-velocity, yank stuff come from? 16:31, 22 September 2006 (UTC)

Mass changing with velocity is a part of relativity; see Mass in special relativity. As for yank, just as "force = mass * accel", "yank = mass * jerk". I'm not sure what original research you are alleging? - grubber 19:23, 22 September 2006 (UTC)[reply]

I am pointing out that there is no source for the information. I am familiar with special relativity. Why should I believe that special relativity is at all relevant to the applications of jerk? Melchoir 19:44, 22 September 2006 (UTC)[reply]

- - I think you make a good point lol. - grubber 01:45, 23 September 2006 (UTC)[reply]

Now jerk is 3rd deriv., which reminds me...people debate/discuss about whether Nature

has a preference for linearity--great. But how about more debate/exploration on Nature's "preference", if the preference exists, for second order differential equations? One way to explore it would be to check if there is something mathematically significant that happens or doesn't happen with linear third order partial differential equations. Does all hell break loose in the solutions or what? This is like asking why we have 3 space dimensions instead of 38 or 190 spatial dimensions.Rich 00:02, 22 April 2007 (UTC)[reply]

Nature has no special preference for the 2nd derivative of position, or of any other. However, the Taylor series (or Maclaurin series) approximation shows that for most of the kinds of functions that describe motion, lower derivatives provide a good approximation to the value of the function. Thus, with important exceptions, you can approximate real-world motion by using lower derivatives. In fact, when you do this, you choose the highest order derivative to use such that the next higher-order derivative term is negligible in value over the domain of interest. This is why considering additional orders of motion derivatives (such as jerk) becomes, in general, an exponentially less interesting to do. David Spector (talk) 14:39, 28 December 2011 (UTC)[reply]

Article move: Jerk->Jerk (physics) and Jerk (disambiguation) ->Jerk

There's no way the majority of English speakers first think of the third derivative of displacement when defining the word Jerk. Thoughts?--Loodog (talk) 16:42, 9 December 2008 (UTC)[reply]

Agreed, most people are probably thinking of the wiktionary definition anyway (of a person). Joshdboz (talk) 20:13, 13 December 2008 (UTC)[reply]

Very little information

This article has very little information beside the physical description and formulae concerning the jerk. It should be supplanted by information from G-force#Rate_of_change_of_acceleration. --Pero-- 78.0.226.174 (talk) 09:38, 28 April 2009 (UTC)[reply]

Further illustration needed

Most readers will not understand the differential equations, and it is difficult to see where the "jerk" comes into the graph provided if you do not already understand the concept. It would be useful to have a graph that shows position, velocity, acceleration, and jerk, separately for the same example. -- Beland (talk) 22:43, 30 August 2009 (UTC)[reply]

I added such and therefore, hopefully with sufficient reason, removed the template. Purgy (talk) 11:37, 22 August 2014 (UTC)[reply]

Third-order motion profile

This section is COMPLETELY WRONG. It needs cleaning. Currently it describes a second-order motion profile with limited positions, velocity and accelerations, but unlimited jerk. Here jerks are "infinite" (a Dirac would be a more precise term) 8 times (at each bounadry of each segment) —Preceding unsigned comment added by 217.154.243.205 (talk) 14:52, 12 August 2010 (UTC)[reply]

This section needs precisions. I believe a graphical representation of velocity and acceleration and jerk could help to make it clearer.

I created this section because I thought there was a problem. Now I realize that there was no problem, but the bot believes I was vandalizing the page while I was correcting my own mistake. OK I did it the wrong way. —Preceding unsigned comment added by 93.2.131.53 (talk) 03:29, 14 August 2010 (UTC)[reply]

I want to express serious doubt about the footnote[3] and smooth fields in classical mechanics and therefore paths belonging to $c^{\infty }$ --Purgy (talk) 12:45, 4 August 2014 (UTC)[reply]

I have replaced the diagramm and changed/edited some content. Purgy (talk) 10:00, 11 August 2014 (UTC)[reply]

Removing snap

The one web page that every article on Wikipedia references says itself the names "snap", "crackle" and "pop" are made up. This is that page http://math.ucr.edu/home/baez/physics/General/jerk.html. I am a physicist and have never seen this term used in any text. I am removing from the see also. For more info see my talk page. To re-add please first provide a reference to a classic physics text that uses the term. Phancy Physicist (talk) 18:01, 10 March 2012 (UTC)[reply]

I see snap, crackle, pop referenced on page 213 of the 2003 physics text book, The Gravitational Million-Body Problem: A Multidisciplinary Approach to Star Cluster Dynamics and page 244 of Physics and Mathematics of Gravitation: Proceedings of the Spanish Relativity Meeting 2008, which is a publication of the American Institute of Physics. The text book references a webpage, that looks to be the source of the math.ucr.edu page linked above, which originated in 1997 http://web.archive.org/web/20100930150942/http://www.weburbia.com/physics/jerk.html Justin Ormont (talk) 01:25, 20 March 2015 (UTC)[reply]

I have no specific meaning about these notions, but never have seen them in some context beyond an enumeration of how to call still higher derivatives. Furthermore, I'm also in slight doubt about a "Multidisciplinary Approach", which is a "textbook" for what audience(?) and I do not know anything about the noteability of "Proceedings of the Spanish Relativity Meeting 2008". My main concern is that I do not want Wikipedia to contribute to arbitrarily generating a meme for some advertisment-names.

Because of lack of background I would not do any editing activities on this. Purgy (talk) 09:16, 20 March 2015 (UTC)[reply]

"...The one web page that every article on Wikipedia references says itself the names "snap", "crackle" and "pop" are made up. ..." The same thing is true of "acceleration" "velocity" and "position", all are made up terms. Your lack of exposure to the names of the higher derivatives is not a good argument against the convention.

166.177.187.229 (talk) 06:07, 30 August 2015 (UTC)BGriffin[reply]

Referring to every word in all languages as being "made up" is not fair when this here is the "making up" of a technical(!) term in very recent(!) times, thereby alluding to mass product's names used in heavy advertising. After this, claiming they were a "convention" is still more unfair.

Summing this up, your arguments "pro" introducing these words weigh less than those "contra", imho. Purgy (talk) 07:21, 30 August 2015 (UTC)[reply]

Non-calculus explanation

This sentence before the diagram: In this way, jerk can seem counter-intuitive, because it is not something people experience qualitatively on a daily basis.

was replaced by this: A familiar example of jerk is the rate of application of brakes in an automobile.

The two examples after the diagram did not appear to be related to jerk, and were replaced by an expansion of the example about applying brakes. Neither of the two previous examples is appropriate to this discussion. The paper-tearing is due to a large acceleration, not jerk. When the force is applied gradually, the amount of force is equal to the muscular strength alone. When the paper is held loose and then jerked tight, the momentum in the hands and arms is added to the muscular strength. The paper attempts a large deceleration of the hands, and the added force is equal to m*a, not m*da/dt. In the case of silly putty, the issue is strictly related to the velocity (as was correctly stated in the text of the example, “the speed with which you pull”), and has nothing to do with da/dt.

RobH103 (talk) 02:11, 24 December 2012 (UTC)[reply]

I added further examples of jerk and I would like to remove the sentence "The higher the force or acceleration, the higher the jerk." after **Equations**, it is simply wrong, imho, but I must try to get aquainted first with the procedures around here, without annoying or offending others.

Furthermore, I am somewhat reserved against necessary limitations in the size of jerk, more above. Purgy (talk) 14:00, 3 August 2014 (UTC)[reply]

After some amendments, I think about removing this section completely. Imho, there are no valid points, not mentioned in other sections, and some propositions must be read with utmost care, not to drop into misunderstandings of the correct notion of jerk. I'll wait for suggestions and thoughts roughly 3 weeks. Purgy (talk) 09:37, 22 August 2014 (UTC)[reply]

I removed this section, including the template requesting additional citations and reliable sources as announced. Purgy (talk) 10:50, 21 September 2014 (UTC)[reply]

New Sections and General Revision

I have added two new section to this page and revised some finessses. I plan to review the whole article, put together the available information and try to streamline some broad unit considerations, thereby also getting rid of the officially deprecated gal. Purgy (talk) 11:13, 7 August 2014 (UTC)[reply]

I made up a diagram showing now the corrected speed, and also jerk and acceleration for the motion control. Feel free to edit, or comment on it. If you revert it, please let me know about the reasons and give me a chance to argue. :) Purgy (talk) 09:35, 11 August 2014 (UTC)[reply]

I regrouped and added some new information. Purgy (talk) 16:49, 12 August 2014 (UTC)[reply]

Split section Jerk Systems to Chaos theory?

I suggest placing the mentioned section of this here articel in the page about Chaos theory, because the importance of the associated 3. order non-linear DEQs belongs largly to the possible chaotic behaviour of their solution and the realisation of these systems in appropriate circuits is also of rather mathematical interest, imho. The conection to jerk in Mechanics is rather restricted to the degree of the DEQs. Thoughts, anybody? Unwithspoken, I'll implement this in roughly 3 weeks. Purgy (talk) 09:19, 22 August 2014 (UTC)[reply]

I did as announced. Purgy (talk) 10:36, 21 September 2014 (UTC)[reply]

Initiating reassessment

After having been hinted to do so, I removed the rating of "Start class" on the quality scale, in the hope to get some advice from the Physics portal how to improve this article further. Purgy (talk) 11:44, 22 August 2014 (UTC)[reply]

Portals don't normally assess articles for quality - that's a WikiProject function, in this case Wikipedia:WikiProject Physics. Somebody there should soon notice that this page is now in Category:Unassessed physics articles (there are presently 25 pages in that cat, a low number compared to, say, Category:Unassessed United States articles); if you need a particularly fast response you could drop a note at Wikipedia talk:WikiProject Physics/Quality Control. --Redrose64 (talk) 12:44, 22 August 2014 (UTC)[reply]

I must confess, that I overlooked that difference between "portal" and "project". This is in no way to express any lower appreciation of both, but only due to my newbie- and sloppiness; and who am I, to need a particular fast response? Lucky, to get sooo much. :) Purgy (talk) 15:12, 22 August 2014 (UTC)[reply]

It has been rated C-Class! I'll look for further improvement.Purgy (talk) 16:41, 9 December 2014 (UTC)[reply]

Newton's laws are consistent with a force depending on jerk

At Jerk (physics)#Jerk in an idealized setting, the article says "Assuming Newton's laws of motion and rigid bodies implies the possibility of discontinuous accelerations.". I disagree. Newton's laws are consistent with a force depending on jerk. All that Newton's laws say about this is that the inertial force ("fictitious" force plus gravity) is proportional to acceleration. It says nothing about whether there are forces, such as radiation reaction, which are proportional to jerk or higher derivatives. If there are such force (which there are), then discontinuous acceleration is impossible. JRSpriggs (talk) 06:50, 11 December 2014 (UTC)[reply]

Hi, @JRSpriggs:, it was me who wrote this, and I admit that the formulation sloppily states something wrong. Would something like

"Assuming a Classical Mechanic's setting, restricted to Newton's laws of motion and rigid bodies with only inertial and constraint forces acting on them, would imply the possibility of discontinuous accelerations."

be OK? The forces associated with higher path derivatives are mentioned in the subsection Higher derivatives, but are not properly delt with. My sole and cheap excuse is my reference to idealized setting. Thank you for any suggestions. Purgy (talk) 08:44, 11 December 2014 (UTC)[reply]

Even if one supposes that non-inertial forces depend only on position and velocity, I would not infer that discontinuous acceleration is possible. Because the dependence of force on

{\vec {r}},\,{\vec {v}}

would presumably be smooth, that is, C^∞ and consequently the forces would be continuous functions of time. JRSpriggs (talk) 16:13, 11 December 2014 (UTC)[reply]

Hi, @JRSpriggs:, how do you think about my examples of discontinuous acceleration along a C¹, but just piecewise C^∞ path (straight line + arc) and of harmonic motion with friction, which I tried to explain in the rest of this section? The same discontinuity would hold in an idealized Geneva drive for the angular acceleration. I fully agree, that discontinuous acceleration in non-idealized settings is impossible, but I am convinced that these discontinuities in the idealized setting show the places where in reality spikes in the jerk are to be expected.

Because of no "beaming" I require continuous pathes and because of bounded forces I require continuous velocities, i.e. pathes, which are C¹, and velocities which are piecewise at least C¹, resulting in bounded accelerations, only showing jump discontinuities, should suffice. Please, explain the reasons for your presumptions of general smoothness to me. I hope, I did not get lost in the C-numbering of continuous, differentiable, smooth, and in combination with piecewise, ... Thanks. Purgy (talk) 17:55, 11 December 2014 (UTC)[reply]

A constraint with no 'give', i.e. an infinite spring constant, is impossible (both classically and quantum mechanically). So confining a particle to a line (either straight or curved) is impossible. JRSpriggs (talk) 09:54, 12 December 2014 (UTC)[reply]

@JRSpriggs: please allow to let me point to the heading (idealized setting), to the assumption of rigid bodies and to the explicit denial of the idealized math representation existing in reality. I am really convinced that confining an abstract point mass (which does not exist!) to an abstract, well-behaved curve (which also does not exist!) is completely de rigeur in lots of renowned text books, without referring to not existing, infinite spring constants. BTW, the second example of unbounded jerk in an idealized setting uses explicitly a finite spring constant. Please, help me to adapt my text to sensible requirements without excluding customary idealizations. Purgy (talk) 11:23, 12 December 2014 (UTC)[reply]

I suggest "While discontinuous acceleration (infinite jerk) may appear in over simplified models, it does not occur in reality.".

As for the example of a mass attached to a spring sliding on a surface with friction — the mass and the surface will be distorted (stretched) near their region of contact. When the mass stops moving at its maximum excursion, the friction force will decrease continuously as the stretching decreases and then they will increase together in the opposite direction as the mass begins to move backwards. So the friction does not change discontinuously. JRSpriggs (talk) 05:35, 13 December 2014 (UTC)[reply]

@JRSpriggs: I hope my edit sufficiently conveys now your reservations against idealized settings, which I had put in less prominent place in the former version. Let me please know. Purgy (talk) 12:11, 13 December 2014 (UTC)[reply]

One cannot really talk about "infinite jerk" because the definition of a derivative does not really allow for infinite derivatives (as one does not always include infinity in the definition of a limit). Furthermore, a discontinuous acceleration has no jerk defined at the point of discontinuity as it is necessarily not differentiable there. On the other hand I have personally always wondered why physicists assume motion functions to be smooth. One does not even need "infinite" jerk for there to be a discontinuity in acceleration; jerk itself will be discontinuous and undefined at that discontinuity.--Jasper Deng (talk) 15:01, 2 September 2015 (UTC)[reply]

On a formal level I fully agree to your reservation against "infinite jerk". Considering the next sentence, do you think that putting "infinite" in quotes would suffice for a prima vista understanding of the situation at hand? Explicitely referring to a theory of distributions, necessary for dealing with these things seems to me to go beyond the scope of this article. If one does not go along the derivative-way, but along the integrating-way, the meanwhile widespread basic knowledge about Heavyside- and Dirac-"functions" would help to an imho good understanding. Purgy (talk) 19:33, 2 September 2015 (UTC)[reply]

Since jerk is defined as a strong (not weak) derivative in the article, we cannot use the language of distributions. Keep in mind that our readers are mostly elementary physics students who have no knowledge of distributions.

"infinite" would be confusing if we don't explain it, and even then, I think it's not the best term to use just because jerk need not approach infinity at a discontinuity of acceleration.--Jasper Deng (talk) 04:22, 3 September 2015 (UTC)[reply]

I took a bold attempt to avoid that "infinite". Hopefully, it's an improvement and reduces your reservation.

Regarding my flawed reversion, I noticed the linked mentioning of "jounce" a bit more down in the article under "Higher derivatives". Do you think both occurrences are sensible? Purgy (talk) 10:12, 3 September 2015 (UTC)[reply]

The vaguer word "unbounded" is definitely better.

As for jounce, I put it in the article lead because not everyone reads every section of the article, nor does everyone want to scroll down to find the link in the "See Also" section.--Jasper Deng (talk) 16:51, 3 September 2015 (UTC)[reply]

All but one reference is dead (404)

All but one of the references on this page gives 404 not found — Preceding unsigned comment added by 5.151.0.2 (talk) 21:19, 2 October 2016 (UTC)[reply]

As of just now, all given links lead to appropriate targets. Maybe there is something wrong with your network permissions? Purgy (talk) 05:59, 3 October 2016 (UTC)[reply]

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Incorrect, compoundly.

"... The beginning of an emergency braking lets the body whip forward faster than the achieved acceleration value alone would accomplish, ..." . As stated, this is wrong in more than one way. . To begin, remember the body does not 'whip forward', it merely continues to travel at the same speed it has been travelling. This might seem like I am picking nits, but the frame of reference is important. Sure you could choose a noninertial frame of reference like the car that has begun to brake, but that just makes things more complicated....so complicated that errors like those made in this statement could be easily overlooked. . Once we are back considering things from an inertial frame of reference, it becomes plainly obvious that the body cannot "...whip forward faster than achieved acceleration value alone would accomplish...", because the body just continues to move forward until acted on by seat belt of otherwise. If anything, looking at the peak acceleration of the car would overestimate the relative velocity of the body with respect to the car. . So to review the ways in which this statement is wrong: 1. The chosen frame of reference weird and overly complicates things. 2. Jerk does not somehow disengage the relationship acceleration and velocity. 3. The direction of the effect, claimed as evidence, is exactly the opposite in reality as that suggested by the claim. . . BGriffin (talk) 19:05, 15 June 2017 (UTC)BGriffin[reply]

Please, have in mind that the effects of jerk are not described by Newton's laws of motion, which of course hold in these circumstances, but are of physiological nature, without violating physics. Living human bodies are neither rigid nor liquid bodies, with forces only acting on them, but exact themselves forces. I have tried to address your legitimate concerns in the paragraph. Purgy (talk) 10:41, 16 June 2017 (UTC)[reply]

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"no generally used term to describe its scalar magnitude"

I don't understand this sentence- no generally used term to describe its scalar magnitude. The next sentence says the units of jerk are m/s³, which is scalar. So it seems that it is just like acceleration which can have both a scalar acceleration value or vector. Volunteer1234 (talk) 13:11, 22 August 2018 (UTC)[reply]

In nitpicking manner one should perhaps say that the unit for Cartesian jerk-components and for the scalar magnitude of the jerk-vector is such and such. In any case I am not aware of a "generally used term" for this magnitude, and also not of any units, directly applicable to vectors. The setting is similar to acceleration, that intrinsically has a vector quality, and, like all vectors, any acceleration vector has a magnitude, which has appropriate dimension and units. I changed accordingly. Purgy (talk) 16:43, 22 August 2018 (UTC)[reply]

Still seems wrong to me. There is a generally used term for jerk's scalar magnitude, and it is jerk, the same as there is a generally used term for scalar acceleration- acceleration. Volunteer1234 (talk) 17:05, 22 August 2018 (UTC)[reply]

Did the last edit address your concerns? I'd like to remark that I avoid notions like "scalar acceleration", because acceleration is intrinsically a vector, the "norm" of which is, also intrinsically, a scalar, which may carry units. It is not the case that arbitrary components of a vector employ the same units (e.g. polar coordinates). I agree that jerk/acceleration are both used to denote the corresponding vectors and their norms - in rigorous contexts such is generally called "abuse of notation". Purgy (talk) 07:07, 23 August 2018 (UTC)[reply]

It is getting better. It now just seems too long and not a very interesting fact for this to be in the small lead. I moved it to the 3rd sentence Volunteer1234 (talk) 17:03, 23 August 2018 (UTC)[reply]

It might well be a matter of taste how interesting it is to make explicit wide-spread abuse of notation, but I won't interfere, if you like it this way. :) Purgy (talk) 07:30, 24 August 2018 (UTC)[reply]

Linguistic inconsistency

I note that the first three terms in the list below are all from Latin, whereas the fourth is not.

position velocity acceleration jerk

What term from Latin could be used to replace "jerk"? — Preceding unsigned comment added by John Link (talk • contribs) 21:25, 25 September 2018 (UTC)[reply]

I side your view these being linguistically inconsistent terms within this connection, but to my knowledge there is no serious contender with an even near frequency of use, and I know of none with Latin or Greek roots. Till someone finds a suitable term with sufficiently documented and frequent use, WP seems bound to stick with alone the inconsistent jerk. Purgy (talk) 07:19, 26 September 2018 (UTC)[reply]

Constant Pedal pressure Braking of Automobile

   The reason for the by far bigger jerk in the first way to brake is a discontinuity of the acceleration, which is initially at a constant value, due to the constant force on the pedal, and drops to zero immediately, when the wheels stop rotating.

Tangentially: I suspect that braking a car with constant foot pressure does not produce constant deceleration at any time. I'm not qualified to fully elaborate, but I suggest that the deceleration increases as speed decreases. Constant kinetic friction between brake pads and discs/drums would suggest a reduction in kinetic energy that is proportional to distance and thus proportional to the square root of speed. This would imply constant deceleration, I think? But it doesn't feel that way! And what is brake fade? Do brakes dissipate heat more effectively at lower speed when absorbing/converting kinetic energy at a lower rate? Undoubtedly. Does this affect performance more than negligibly? Does it explain the cause of my perception? Are there other factors to consider? I'm not sure. But...

The section that describes this process as an example of induced jerk is in error, although it achieves its primary goal of elucidation. I believe the deceleration curve becomes steep near the stop, but is always sloped and continuous. — Preceding unsigned comment added by Bill Michaelson (talk • contribs) 13:15, 3 January 2019 (UTC)[reply]

Assuming usefully idealized settings I think about it this way: Constant pedal pressure implies constant pressure of the pads on the disc (no non-linear servos, ...); this implies constant braking torque on the disc (=wheel) as long as it rotates (simple model of kinetic friction, ...); this yields constant angular deceleration (mass dependent) of the disc as long as it rotates; constant angular deceleration implies linear decrease of angular speed of the disc (~speed of the car). Exactly when the linear (angular) speed-over-time graph crosses the zero-speed line, the hitherto constant (braking) torque on the disc collapses to zero (It is now also independent of the pedal pressure! You cannot accelerate your car by going on "braking".), and also the hitherto constant negative acceleration collapses to zero, and this collapse generates the (idealized: infinite) jerk.

Maybe emergency braking does not obey the simple rules for kinetic friction, in which the frictional force is simply proportional to the normal force and independent of the speed, and certainly, the effect is masked by the suspension and other deformations, but the collapse of the braking torque exactly at standstill remains. BTW, all rules of thumb to estimate breaking distances assume constant (=maximal) deceleration across the whole braking process. Purgy (talk) 15:03, 3 January 2019 (UTC)[reply]

Incorrect explanation?

Section Physiological effects and human perception: The feeling of being pressed into the seats in a high-powered sports car is the force of acceleration. Jerk only occurs initially when the engine torque increases from zero, causing a remarkable increase in acceleration (jerk).

I don't think that's correct. As a vehicle's velocity increases, so does air resistance, decreasing the acceleration until it reaches 0 at the vehicle's maximum velocity. Does this not mean that there is a jerk throughout the period of acceleration? The jerk would be a large and positive at the initial acceleration, then small and negative until acceleration returns to 0 at maximum velocity.

I've amended the explanation to avoid having to remove it. However, it seems to me that the relevance to physiological effects is more in the acceleration than the jerk, and the example may not be appropriate in that section. Thtatithticth (talk) 04:03, 5 March 2020 (UTC)[reply]

Wikipedia:Articles for deletion/Crackle (physics) (4th nomination)

This deletion debate may be of interest to those watching this page. XOR'easter (talk) 19:22, 14 March 2020 (UTC)[reply]

Should it say "CAM profile" every time it says "cam profile"?

I'm guessing "cam profile" may refer to Computer-Assisted Manufacturing, related to CAD (computer-aided design), which is one of a few contexts where I have encountered the concept of jerk (mechanics).

The word CAM should be uppercase, and maybe it should be a bluelink (wiki link) the first time it appears. Unless it is referring to cams, the wheels that are not round, or something else. Cams do have a profile or shape, it determines how they move the thing they push as they rotate.

This article doesn't prominently mention feedback systems of any kind, and actually enforcing a jerk limit requires feedback from the moving part. This is especially true in the elevator example, where the mass of the moving elevator car is variable depending on the passengers. But it is variable even within a robot, as the motor gets weaker or the friction increases, and a fixed program that worked during R&D starts to fail in the field with older devices. Those are some nightmares I hadn't thought about in five years. Ahh, engineering. 209.94.144.13 (talk) 21:16, 24 December 2020 (UTC)[reply]

At first I disagreed, but on second look I think you're right about the 'in manufacturing' subsection of 'motion control.' The wording is ambiguous, and reads like following a cam profile, but the parent section implies that this is a CAM motion profile Strangerpete (talk) 11:24, 25 December 2020 (UTC)[reply]

History?

When was the first time it was called "jerk" and why? George Rodney Maruri Game (talk) 00:06, 30 March 2023 (UTC)[reply]