Talk:Bouncing ball

Related projects on commons and wikiversity
I was too busy to read your article carefully, but it looks good. You may be interested in some links that are already on commons:
 * File:Happy_vs._Sad_Ball.webm is a video illustrating how an elastic collision to a heavy object delivers more momentum than does an inelastic collision. Please consider either a link to this video, or perhaps placing it in this article.  A strong reason for doing so involves using Wikimedia as a vehicle for allowing young people to establish reputations via Creative Commons works.  This video was produced by an undergraduate student user:13hartc.
 * How_things_work_college_course/Momentum_transfer_under_elastic_and_inelastic_collisions is rather sloppy and disorganized effort conducted with a couple of classes to model this theoretically. We could not get a good match between theory and experiment.  This should probably be linked as a Wikiversity sister link.  If you wish, I will make that link for you.
 * Advanced Classical Mechanics/Compound ballistic pendulum with spinning ball is a calculation that I did, with a bit of student input described as follows: I posted the calculation on Wikiversity and conducted a lab for calculus-based physics majors that worked as follows: Each pair of students was assigned a portion of the calculation.  They were to assume that all preceding formulas were correct, and only check the algebra up to the end of their assigned portion.  I'm not sure how it worked...I probably should have assigned it later in the course.--Guy vandegrift (talk) 14:28, 16 February 2017 (UTC)


 * Hi, thanks for the links. I've given them a quick review, and... well my initial impression are as follow.


 * Concerning the video, I feel it a bit of a bad demonstration because it is unfocused on what exactly it wants to highlight. On a technical level, the interesting aspect of this video would be what happens at the impact for each of these balls, but we don't really see what's happening with great clarity. Two ball roll down and bounce. If you pay attention, you'll notice the ball falls in the gap and makes the block wiggle, while the second one bounces back and makes the block fall. My suggestion for your student (if you're the one supervising them) is to
 * Shoot the video to have a side view of the ramp and put the block flush against the ramp in both cases. The gap between the ramp and the block is a distraction and prevents an apple-to-apple comparison of the two situations. The sideview highlight the 2D-nature of the situation, and should be shown accordingly. Having a sideview will clearly show the recoil of the block in both cases, as well as bouncing distance.
 * Use a tripod/fixed camera
 * Start with the happy ball, as this is what most people would expect a ball to behave like.
 * Put a ruler on the side of the ramp, this way we can have sense of scale and see how far back the balls bounce.
 * If that student isn't around anymore, making such a video could be project for another student. But as the video stands, I'm very ambivalent about including it in the article. I feel it would muddy the waters more than it would clarify them. There is an argument that we don't link to any free (libre) videos, and I'm partial to that, but I'm not convinced the quality is high enough to be useful here.
 * Concerning the Wikiversity stuff, I'm not quite sure what the policy on linking to materials from Wikiversity is. It certainly doesn't pass as a WP:RS, and we'd be linking to material such as " The simplest theory says that happy is fully elastic and sad is fully inelastice, and the sad/happy pathlength ratio is 4." which (on top of the poor grammar/spelling), stands out as an very unclear and unsubstantiated claim. And the later analysis completely neglects the rotational energy gain by the ball as it goes down the ramp, which cannot be neglected here, and the energy needed to knock the block will depend on the geometry of the block. But if linking to such material is done in other articles / if Wikiversity is treated like other sister projects (e.g. Commons, WikiSpecies, etc.), I'm not objected to have the usual linking templates added to the see also/external link sections. Headbomb {talk / contribs / physics / books} 15:33, 16 February 2017 (UTC)

GAN, deflategate, bouncing and gauge pressure
I read this article and considered reviewing it for the GAN, but I do not have enough technical expertise in mechanics to feel competent to verify most of the content. I also feel it would be a better process for me to nominate an article and learn from the feedback provided by a reviewer. If it goes another week lacking a reviewer, though, I could probably be persuaded to just jump into the deep end, maybe with a mentor? I do have a question, though, about the last paragraph, first sentence: "The bouncing of a gridiron football was at the center of the deflategate controversy." Bouncing is not mentioned in either of the references provided, but the Well report does quote Tom Brady on page 40, commenting on the inflation level of the balls during an earlier game: So my question is: are you using "bouncing" as a synonym for "inflation level" in this context? It is true that gauge pressure is correlated with bounciness, and gauge pressure is what is regulated by the NFL, but bounciness was not really the issue — it was whether Brady gained an illegal advantage being able to grip and throw a softer, lighter ball. It's misleading/inaccurate to say that the bouncing of the gridiron football was the issue at the center of the controversy; it would be more accurate to say, "Gauge pressure was at the center of the deflategate controversy." Cheers! — Grand&#39;mere Eugene (talk) 22:05, 19 February 2017 (UTC)


 * It's... I suppose it depends on how picky you want to be. In general if I throw something at you, and you want to catch it, you can consider the ball as making an impact with your hand. If it's deflated, it will have a lower coefficient of restitution, thus bounce less, and thus be easier to catch. If you inflate it more it will be bouncier, and thus be harder to catch. If you want to say this is about the gripping properties you wouldn't be wrong either, with the subtle difference that there is no impact (thus bounce) when you throw a ball, only when you catch it, and the gripping properties also cover other things like friction. So deflate gate is partially, but not purely, about the bounce of a gridiron football.


 * If this is something you think needs to be clarified, we could go with "The pressure of a gridiron football was at the center of the deflategate controversy." instead. Headbomb {talk / contribs / physics / books} 00:39, 20 February 2017 (UTC)
 * Thanks for your explanation. The revision you propose is obviously supported by the sources, and would be better, especially if the article is read by fans of American football! Cheers! — Grand&#39;mere Eugene (talk) 01:07, 20 February 2017 (UTC)


 * Done. Headbomb {talk / contribs / physics / books} 01:11, 20 February 2017 (UTC)


 * Isn't "Deflategate" treated as a proper noun (and hence capitalized)? —Quondum 02:20, 20 February 2017 (UTC)
 * NYT and ESPN both capitalize it, but NPR does not. Grand&#39;mere Eugene (talk) 02:28, 20 February 2017 (UTC)

magnitudes and signs ...
From [note 1]: "Here, v and u are not just the magnitude of velocities, but include also their direction (sign)."

This is confusing to anyone with a bit of background of Euclidean vectors (adding a sign to a magnitude is undefined), so clarification might be appropriate. Should it be "Here, v and u are the single component of the velocities, including sign, where all motion is one-dimensional."? —Quondum 18:12, 20 February 2017 (UTC)