Talk:Bouncing ball/GA1

GA Review

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Reviewer: Reyk (talk · contribs) 12:28, 30 October 2017 (UTC)

I'll start on this in the next day or so. First impression is very positive. Reyk _YO! 12:28, 30 October 2017 (UTC)

OK, so I've had a careful read through the article and it is very close to being passed as a GA. The most obvious criteria are fulfilled already: a high standard of writing, complete and accurate sourcing, no copyright issues that I can detect, and a sensible selection of images. My major concerns are that it's a bit math-heavy, and that it lacks a discussion on the history of the scientific investigation of bouncing balls. I'd also suggest moving a few of the images to the left to break up the monotony of them all being on the right side. In the next few days I'll go through the article thoroughly, section by section, and make a few specific suggestions, but I don't see any reason why this can't be passed within a week or so. Nice article! Reyk _YO! 18:51, 31 October 2017 (UTC)

Lead

Well written and representative of the rest of the content, if perhaps a little brief. Adding a few words on the historic importance of investigating the physics of bouncing balls would help in this regard.

Well, historically speaking, it's not a very important topic. The physics of bouncing balls has been mostly used as a teaching tool, since in the simplified version it illustrates projectile motion rather well, and you can talk about energy losses at impact and so on. This is done at the high-school level and first year university level. In more advanced courses (2nd/3rd year physics), you'll simplify less, adding air resistance into the picture, sometimes using the bouncing ball as a problem to be dealt with numerically. The real importance is in sports engineering, but there's little historical aspect to it. The coefficient of restitution has a lot more history, but bouncing balls themselves have very little "prior research" on them. I could try to dig really old examples (e.g. Mesoamerican rubber balls), but we'd veer into WP:SYNTH territory very soon. There's plenty of history available on balls in general, but very little on their physics. Headbomb {t · c · p · b} 21:16, 9 November 2017 (UTC)

Added a bit. Headbomb {t · c · p · b} 17:02, 19 January 2018 (UTC)

Forces during flight and effect on motion

This looks OK.

Gravity

This looks OK.

Drag

This is all pretty much OK, but it would perhaps benefit from an example of a kind of ball with low Reynolds number where the Stokes Drag effect dominates.

Any ball moving at a very low speed. For a ping pong ball in air, we'd be talking ~1 mm/s to get Re = 1, less for larger balls, which is something that would never be encountered in actual sports. A 5mm ball bearing dropped in a viscous liquid such as oil would have a much better chance of having low Reynolds number (Re = ~1 if v = ~5.4 cm/s), since the combination of buoyant forces and drag will be much much larger, and the ball will be moving much slower (terminal velocities ~1.5 cm/s). I could expand this. Headbomb {t · c · p · b} 21:34, 9 November 2017 (UTC)

I feel this is adequately covered by "In reality, flow is never inviscid, and the Magnus lift is better described by..." Headbomb {t · c · p · b} 17:13, 19 January 2018 (UTC)

Magnus effect

I don't understand why the paragraph on ball tampering is in this section. Did these instances of ball tampering involve changing the spin characteristics of the ball? If so, that should be clearer.

• On a related note I seem to remember other Cricket-related controversies where the pitch was tampered with (by running on it unnecessarily, or poking at cracks), to change the way the ball bounces off it. That might be relevant later in the Impact section?

I don't know if the 2006 instance in particular involved with messing with aerodynamic properties, but in cricket, that's generally why you do it. Not really sure what is unclear here, but I'm open to suggestions. Headbomb {t · c · p · b} 21:38, 9 November 2017 (UTC)

Buoyancy

All fine.

Impact

This is all OK, but perhaps a few words on how impact velocity affects the COR.

I can add that. e slightly increases with the impact velocity generally speaking, as the ball will deform more, thus heat up more. Headbomb {t · c · p · b} 21:40, 9 November 2017 (UTC)

Added "In general, the ball will deform more at higher impact velocities will lose more energy, decreasing its COR." Headbomb {t · c · p · b} 17:13, 19 January 2018 (UTC)

Spin and angle of impact

This is all good, well written and informative.

Non-spherical balls

Again, this is all good. Earlier, the article says the COR can exceed 1 in the case of, eg, a spring-loaded impact surface. It might be worth briefly mentioning there that rotational velocity can influence this too.

That's covered by "Because it is possible to transfer some rotational kinetic energy into translational kinetic energy..." Headbomb {t · c · p · b} 17:14, 19 January 2018 (UTC)

Multiple stacked balls

This is well sourced and interesting, particularly the applications to astrophysics.

Sport regulations

Also fine. I would suggest adding Australian Rules Football, because that is the most significant oval-ball sport in which bouncing the ball is a major part of the game: [1]

Added. Headbomb {t · c · p · b} 17:28, 19 January 2018 (UTC)

Status query

Reyk, Headbomb, it's been over two months since the article was last edited, and over six weeks since the last post to this page. Where does the review stand, and how much work remains to be done on the article? Many thanks. BlueMoonset (talk) 02:48, 14 January 2018 (UTC)

• I'm done on my end. Once the suggested changes are done I am happy to promote this. Cheers! Reyk _YO! 08:08, 14 January 2018 (UTC)
• Right, I forgot about this with work flaring up and other projects. I'll get to this by the end of the month. Headbomb {t · c · p · b} 12:54, 14 January 2018 (UTC)

@BlueMoonset: I added a couple of things, let me know if there's anything more you need. Headbomb {t · c · p · b} 17:30, 19 January 2018 (UTC)

It's not up to me, Headbomb, it's up to Reyk, who's the reviewer; we'll see what Reyk says. BlueMoonset (talk) 20:02, 19 January 2018 (UTC)

@BlueMoonset: doh, my bad. Mixed up who was the reviewer after so long! Headbomb {t · c · p · b} 22:46, 19 January 2018 (UTC)

All done

OK, I had another read through the article and I think it's good to go. The bit about the ball tampering in cricket still is a bit lacking in context but that's not a dealbreaker, so I'm going ahead and promoting this article. Thanks for improving the encyclopedia. Reyk _YO! 11:22, 21 January 2018 (UTC)