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Wikipedia:Featured picture candidates/Projectile motion

< Wikipedia:Featured picture candidates

Projectile motion

edit
Reason
Scraped off of COM:FPC, where voting is at 6/0/0. Plus good enc value.
Proposed caption
A bouncing ball captured with a stroboscopic flash at 25 images per second. Note that the ball becomes significantly non-spherical after each bounce, especially after the first. That, along with spin and air-resistance, causes the curve swept out to deviate slightly from the expected perfect parabola. As the ball falls freely under the influence of gravity, it accelerates downward, its initial potential energy converting into kinetic energy. On impact with a hard surface the ball deforms, converting the kinetic energy into elastic potential energy. As the ball springs back, the energy converts back firstly to kinetic energy and then as the ball re-gains height into potential energy. Energy losses due to inelastic deformation and air resistance cause each successive bounce to be lower than the last.
Articles this image appears in
Parabola, Trajectory, Energy, Coefficient of restitution, Inelastic collision
Creator
User:MichaelMaggs

*Support Nice picture, enc content --Muhammad Mahdi Karim 16:03, 7 October 2007 (UTC) Support edit 1. Muhammad Mahdi Karim 18:11, 9 October 2007 (UTC)[reply]

  • Support Support original, edit 1 not too bad — Excellent caption. If only every other featured picture candidate had a description like that. ♠ SG →Talk 18:19, 7 October 2007 (UTC)[reply]
    • This new version, while certainly much better-looking, drops the resolution (not a primary concern, it's still very good) and makes it more difficult to see the warping effect of the ball after each bounce, due to the ball looking like it's being gobbled up by the shadow. ♠ SG →Talk 18:18, 9 October 2007 (UTC)[reply]
  • Support Support edit 1 - Enc and very well done - Alvesgaspar 19:23, 7 October 2007 (UTC)[reply]
  • Comment, looks good, but I'd be interested in seeing more about your methods for doing this: how you captured it, equipment, software used, etc. since you don't have a reliable source (since you did it yourself) we need to know as much as possible. gren グレン 03:41, 8 October 2007 (UTC)[reply]
Ball, Canon camera (see EXIF for details), tripod, strobe flash set at 25Hz, black velvet for contrasting background, Photoshop CS2. To get a reproducible bounce the ball was released down a cardboard tube fixed above a solid table, and the camera triggered at the same time. The shutter speed was 1.6 seconds, but since the room was dark the ball can be seen only when the flash fires. This was repeated about 100 times to tweak the settings and get a pleasing-looking result. --MichaelMaggs 06:25, 8 October 2007 (UTC)[reply]
  • Comments. Firstly, I assume this is a basketball, and if so that probably should be stated in the description rather than just 'ball'. Secondly I have a bit of an issue with the very first ball - to be honest it doesn't look right. It appears to be dropping almost vertically, in which case the ball wouldn't bounce off at that angle. I can guess at some possible reasons, one being that ball initially was thrown with a fair amount of topspin, another is that the ball was bouncing away from the camera (which is likely part of the explanation as the balls get smaller from left to right), or thirdly that the first ball was added in later and put in the wrong position. I wonder if you'd be able to explain? Thanks. --jjron 08:45, 8 October 2007 (UTC)[reply]
It's not a basketball but a child's ball about the size of a tennis-ball. The first image is in the correct place - none have been moved - and resulted from the ball being dropped down a tube secured at a fairly steep angle, to get consistency of bounce. As a result of the ball falling/rolling down the tube there would have been some spin imparted (and indeed you can see that by comparing consecutive images). The plane of the bounce was so far as possible perpendicular to the camera axis, but since the camera was only about 40cm from the first bounce, the ball would inevitably be moving away from the lens during the second bounce. The ball-sizes could have been corrected in Photoshop but I prefer to keep the sizes and positions exactly as they were captured by the flash. --MichaelMaggs 11:29, 8 October 2007 (UTC)[reply]
  • Ah, OK, with no scale and no identification there's no way of telling what this ball is (I think the type of ball does matter a bit, as you identify in various captions the ball deforms significantly, but this would vary of course with different balls). I'm happy enough with your explanation that the first image is as captured without any alterations. --jjron 07:58, 9 October 2007 (UTC)[reply]
Size of ball has been added to description. Thanks for the suggestion. --MichaelMaggs 17:26, 9 October 2007 (UTC)[reply]
  • Weak Support Consensus Version per above discussion. Weak as I would prefer the ball to not be moving away from the camera (the camera would need to be mounted more centre on to the whole thing). I would also prefer to see either the incoming first ball dropping from it's full height rather than 2/3rds of the way to the ground, or otherwise probably not be there at all, so that you'd just see two neat curves. Overall it's pretty well done though. --jjron 08:04, 9 October 2007 (UTC). The edit is sharper, etc, but the same concerns stated here still apply. --jjron 06:22, 11 October 2007 (UTC)[reply]
  • Adding edited version as Edit 1 by Richard Bartz:
 
Edit 1
 
comparing the sizes of the basketball on the first bounce and the last bounce shows the dramatic distortion
  • Oppose Initially I wasn't sure what to think about this image. But after seeing it a few times I am convinced there are fundamental problems. The biggest problem is the distortion. To properly show projectile motion, which is a phenomenon that happens along a plane, the camera should capture it straight-on. The nominated image also has so much overlap at the peak of the bounce that it is hard to resolve the projectile's motion. I'm also not happy with the lines on the projectile, which do not provide any information but only distraction, and the exposure of the ball is very uneven. I have seen these types of images before, even making some of them myself in high school, and we always use a gridded background to provide a scale, something that is standard practice in motion capture photography (see Eadweard Muybridge, several examples). Jeff Dahl 20:42, 9 October 2007 (UTC)[reply]
  • Support Edit 1 --Central Powers 21:37, 9 October 2007 (UTC)[reply]
  • Support edit 1, the distortion isn't ideal but I don't think it really lessens its usefulness for any of the articles. gren グレン 02:13, 10 October 2007 (UTC)[reply]
  • Query: Several people have suggested the image would look nicer without the first ball. I don't feel strongly either way, but getting rid of it would save the queries about whether it is in the right place (it is). On the otheer hand I really don't want to have to re-start the voting all over again. Would deleting it be a small enough edit to avoid having to ask everyone to re-vote? Perhaps that could go up as an Edit 2 option?-MichaelMaggs 20:02, 11 October 2007 (UTC)[reply]
    • I would support removing it, but then again I think it was my suggestion. It looks like this is going to be promoted anyway, and as you said you'd have to ask everyone to revote as this is getting close to closing time. I'd like to see the edit myself though. --jjron 06:38, 13 October 2007 (UTC)[reply]
  • Let's leave it now. --MichaelMaggs 10:30, 13 October 2007 (UTC)[reply]

Promoted Image:Bouncing ball strobe edit.jpg -- Chris B • talk 14:02, 17 October 2007 (UTC)[reply]

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