# Talk:Impulse (physics)

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## Old posts

I've moved the existing disambiguation information (small compared to the physics description) to a disambiguation line at the front of the article. I think this ought to be enough. However, it's always possible to create an impulse (disambiguation) article to deal with the alternative uses. Ian Cairns 18:08, 3 Oct 2004 (UTC)

The article does not mention Ns (Newton Seconds), which I believe is the more commonly used unit for impulse to distinguish between Momentum and impulse. It may be wise to state that Ns= kg m/s²x s = kg m/s, so while they are the same unit, Ns is used more frequently. Wheatleya 19:28, 9 November 2005 (UTC)

## Fixed Terminology

First of all, impulse is not defined as change in momentum. (It's equal to the change in momentum of an object, but that's not the definition.) I put the definition first. Also, you don't say "an impulse..." any more than you say "a momentum". Impulse is a quantity. To say "an impulse is a change in momentum" makes it sound like impulse is an event, which is not correct, at least not in this context. Pfalstad 05:24, 19 April 2006 (UTC)

I think its perfectly fine to say "an impulse". It seems natural to say "apply an impulse". However, saying something to the effect of "apply a momentum" seems unnatural. I don't think that differentiating "an impulse" (in electronics) from "the impulse" or something (in physics) is a good way to differentiate them. Fresheneesz 07:11, 19 April 2006 (UTC)

Of course it's fine to say "an impulse", it's just not how the word is used in physics. Saying "apply an impulse" is using the word in a nontechnical sense. Unless you can provide a source (physics text) that uses the term in that way. Pfalstad 03:58, 21 April 2006 (UTC)

## Disambig

I think this page should be a disambig page, and be moved to Impulse (physics). There are a bunch of other definitions of impulse, and impulse in physics isn't even a decently large concept. Any takers? Fresheneesz 07:11, 19 April 2006 (UTC)

## removed outdated merge tag

I removed the merge tag, its old. And on the talk page for momentum - we are comming to the conclusion that we should move all that info here for good. Fresheneesz 08:21, 19 April 2006 (UTC)

## Impulse (physics)

An article of this name was created today with a definition of impulse = rate of change of acceleration, instead of impulse = change in momentum. A merge was proposed, which I've boldy edited into a redirect to this article. I've saved the ext refs which confirmed the correct definition of impulse - as in this article as of now. Ian Cairns 00:43, 6 June 2006 (UTC)

## Impulse is J or I?

I know this is really trivial, but shouldn't J be used to stand for impulse? that's what's used in my textbook Physics for scientists and Engineers with modern Physics, Douglas C Giancoli, Prentice Hall, Third edition (in case someone wants to look it up). 'I' stands for electric current, not impulse. (ever heard p=iv? that means power=current times voltage, not impulse times voltage).

## are you sure?

are you sure that "dt is an infinitesimal amount of time"?

that is an integration statement, and "dt" would usually mean "with respect to t"

• You are correct that dt is an integration statement of time, but the application of dt mean "the limit of time as it approaches zero", which means an infinitesimally small amount of time. Wizard191 16:46, 11 January 2007 (UTC)

## What's a Hy unit?

Right now it claims that a N-m = Hy (Huygens), which is a unit name I have never heard of. Upon research I haven't found it used anywhere else on the internet or wikipedia. Moreover, the SI system doesn't reference it at all. If this is a real name of a unit please cite it, otherwise I propose that we remove it, as it is quite confusing. Wizard191 16:50, 11 January 2007 (UTC)

I looked everywhere for a unit of Hy. It sounds like a neat addition to physics, and one that the people who head up the SI units should add, unfortunately it is by no means official or correct. I'll continue to look out for it, but I'm removing it until it can be verified. 10 months of an unvalidated claim is quite long enough. —Preceding unsigned comment added by 129.22.18.156 (talk) 05:49, 7 October 2007 (UTC)

Adding to my comment above, the Hy is in fact a fictitious unit of momentum/impulse. It does not appear on the BIPM's website of offical SI units, and therefore it is false and should not appear on this page. —Preceding unsigned comment added by 129.22.147.117 (talk) 17:43, 8 October 2007 (UTC)

it's so seldom to actually compute a momentum of a moving body that there's no need for an extra unit, it's useless (if you need to just write Ns). though i've heard of the unit before (seen it pre 2006 in a german school book). given that it is a school book, there might be justification for a momentum-unit, since school books mostly don't go into real depth but do more of the "we get familiar with the quantities we use" stuff. so that might be a reason why someone made up the unit Hy. 92.196.80.110 (talk) 21:44, 12 September 2013 (UTC)

## Force of Impact?

Often one hears the term "Force of Impact". Say you can calculate/estimate the impulse of an impact but you want to estimate (perhaps) the maximum force of collision, or possibly the average force of the collision, or maybe even the average force for the top 25% of the most forceful moments of the collision. Is any of that information relevant? I'm interested in the relationship between the fracture strength of materials and "how forceful" an impact an object of said material can take. It would seem that Impulse is a desired quantity to know, but what else should I know? IIRC to get average force, I just divide divide the impulse over the time it takes for the the impact to take place. But how would one estimate this time? How would I estimate the average force imparted by one billiard ball on another over the lifespan of the impact, which I cannot estimate with the unaided eye. How high could I drop a billiard ball in a frictionless environment from a building before cracks of a certain size develop on its surface (I.E. the force imparted exceeds locally the fracture strength of the material the billiard ball is made from but it does not fracture the ball). How do I estimate how much effect the ground chosen for the ball to impact has on this? If the fracture strength of the ground is quite low, energy from the impact will be dissipated by "flakes" of the ground being thrown outward, and it would seem that also needs to be taken into consideration.

It seems methods to estimate information is relevant and related to the article, but no description or references are included in the article. What quantities are these and how are they measured or estimated?

I'm not a physicist and I wouldn't even know where to begin to look (other than, say, research into stuff like bicycle helmets).

Root4(one) 17:46, 10 March 2007 (UTC)

This is now a question on Wikipedia:Reference desk/Science. Root4(one) 04:03, 12 March 2007 (UTC)
Tough question. Many people will confuse you by saying double the static load. That's a bit weird, it makes lots of assumptions that are unsafe. The best way for many problems is to work out a stiffness function for the target, and an effective mass for the impactor, and to do a simulation of it. Greglocock 12:07, 13 March 2007 (UTC)
Answered on that page.Greglocock 01:11, 14 March 2007 (UTC)

## Major rewrite

The general definition of impulse was moved to the beginning of the article, and the special case which once appeared there was moved lower down.

Reference to the "Theorem of Impulse and Momentum" was removed, since it is trivial (a three-line derivation appears in the very article) and does not even appear by that name in any of the mechanics textbooks I have: Kleppner & Kolenkow, Tipler, Young & Freedman, and Marion & Thornton. Mention of Newton's Second Law now precedes the derivation.

I added the fact that the special case given relies on both force and mass being constant; previously, only force was mentioned as constant. A common example in which the mass of a system is not constant is the problem of a rail car from which sand is leaking.

Finally, there were minor stylistic changes.

Anarchic Fox 20:05, 19 June 2007 (UTC)

## Math?!

Who decided that Impulse defaults to the mechanical definition? Perhaps most people would be looking for the psychological definition? --Nathanael Bar-Aur L. (talk) 04:21, 24 August 2008 (UTC)

It appears most likely that the mechanical definition of Impulse was the first application of the word to be given an article in Wikipedia. The other applications, including Impulse (psychology) came after that. When you select Impulse the top line in the article is a link to the Impulse (disambiguation) page. This is a common solution found in Wikipedia for many concepts that have two or more applications. If a Wiki User wants an alternative application to be the subject of the default article, or wants the disambiguation article to be the default, this is a legitimate topic to raise for discussion on the pertinent Talk page. Dolphin51 (talk) 11:52, 24 August 2008 (UTC)

## Context Tag: Introduction Needed

I have tagged this article as having insufficient context for readers with less understanding of the underlying physics and math involved in impulse, momentum and velocity. I'm not suggesting that the article needs to be "dumbed down", but if there's someone out there with good knowledge on this subject, I think this article could really use a well-written Introduction that explains Impulse in reasonably understandable prose, which could then lead in to the more technical explanation already contained within the article. Good examples of this would be the pages for Momentum and Velocity, which are both related to this article, and explain their concepts a bit better before jumping right in to the mathematical and theoretical explanations. TrufflesTheLamb (talk) 01:39, 22 January 2009 (UTC)

Thanks to Greglocock for putting together a well-written intro. I have removed the context tag; if anyone disagrees, please feel free to bring it up here! TrufflesTheLamb (talk) 18:15, 22 January 2009 (UTC)

## Page move

Moving this page is a drastic action that I don't necessarily agree with. Can we please get this reverted and discuss this first? I don't see how this isn't the most prominent target. Wizard191 (talk) 22:23, 9 March 2010 (UTC)

Agreed. I've never heard the term Mechanical Impulse. Greglocock (talk) 00:54, 10 March 2010 (UTC)

## Misuse of Notation

After the "therefore" statement in the "Mathematical derivation in the case of an object of constant mass" section, a misuse of notation is used to seemingly "cancel out" the 'dt's in the integration expression,. This should instead be a statement of the Second Fundamental Theorem of Calculus to derive the impulse-momentum theorem. While the "cancelling" is a subtlety that provides the correct results, it could mislead readers. A change could look like

\begin{align} \mathbf{I} &= \int_{t_1}^{t_2} \frac{d\mathbf{p}}{dt}\, dt \\ &= \mathbf{p_2} - \mathbf{p_1} \\ &= \Delta \mathbf{p}, \end{align} — Preceding unsigned comment added by 131.225.23.168 (talk) 07:08, 22 June 2012 (UTC)

## Example section

The "Examples of impulse" section does not appear to add any useful information to the article, and is completely original research. I suggest that it be removed or reworked into something more concrete. - HectorAE (talk) 18:54, 5 March 2013 (UTC)

Agreed. Even worse, it's a collection of unconnected statements, half of which are wrong. — HHHIPPO 21:21, 5 March 2013 (UTC)

## impulse, momentum, superfluous.

it's confusing to distinguish. for example, in german you don't distinguish between the two at all. it's the same (both are called "Impuls"). a moving body has a momentum. if you apply a force to it over a certain amount of time, you change its momentum (thus momentum has unit Ns = Hy, force times time). it's such a basic thing that it's unnecessary to make a big fuss about distinguishing between this. it doesn't help. the unit Ns = Hy is useless / never needed, unless it's the first lecture of mechanic and you want to work a bit with those basic expressions. you never actually calculate a momentum of a moving body and compare "oh look, this body has impulse 3 Ns", rather the velocity or relations between the momenta of two colliding bodies. put the stuff in this article in the momentum-article and delete this one, it's nonsense. 92.196.80.110 (talk) 21:37, 12 September 2013 (UTC)

and if you read the article carefully, you see that there is no content other than stating over and over that impulse and momentum are the same thing. it's artificial inflation of a trivial fact to article size. 92.196.80.110 (talk) 00:23, 13 September 2013 (UTC)

I am afraid you are wrong. Impulse is a change of momentum, not momentum itself. In English we find it useful to differentiate between the two, for instance with rockets. This is an English encyclopedia.Greglocock (talk) 01:15, 13 September 2013 (UTC)