Timeline for Why does a ping pong ball bounce higher when it is dropped together with a cup of water?
Current License: CC BY-SA 4.0
40 events
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| Jun 30, 2020 at 7:09 | comment | added | Russell McMahon | A Lemon Tea my dear Watson. | |
| Jun 30, 2020 at 6:24 | comment | added | Will | @Gert, it's the same one question, about improving your answer by correcting its erroneous first sentence. I'm not going to stand in your way if you're about to learn the same point experimentally. Your answer already contains good content which you're under no obligation to improve, whether in response to comments or new experimental data, so I'm sorry you've found my comments tiring. | |
| Jun 30, 2020 at 5:27 | comment | added | Gert | @Karl: Size comparison, then lemon tea! ;-) | |
| Jun 30, 2020 at 5:27 | comment | added | Gert | @Will I'm getting VERY tired of answering a multitude of questions while trying to organise tests with a steel can at the same time. Please formulate your own answer if you don't like mine. Best regards. | |
| Jun 30, 2020 at 5:14 | comment | added | Will | @Gert you've now made three different appeals to the importance of permanent deformation which you're throwing around interchangeably. Your answer opens by arguing that it's crucial for an inelastic collision and therefore the main reason the cup and water lose kinetic energy; your comments have argued that it's an important part of the E equation, even though the final inequality in your answer eliminates it, saying "it is small"; and then you claim the importance of deformation on the deceleration profile of the cup, which you don't mention in the answer. Which is it? | |
| Jun 30, 2020 at 0:49 | comment | added | F Chopin | What's the lemon for? | |
| S Jun 29, 2020 at 20:09 | history | mod moved comments to chat | |||
| S Jun 29, 2020 at 20:09 | comment | added | David Z | I've created a chat room to preserve the comments here. These are good comments, suggesting changes and improvements and pointing out possible shortcomings of the answer, but there are a lot of them and I wanted to delete the ones that have already been addressed. | |
| Jun 29, 2020 at 19:00 | comment | added | Gert | @PhilipRoe On the basis of the E equation I'm inclined to agree: $W\approx 0$ for a sturdy can. | |
| Jun 29, 2020 at 16:54 | comment | added | Philip Roe | @Gert Excellent. My prediction is that the ball will rise higher/ | |
| Jun 29, 2020 at 16:48 | comment | added | Gert | @Will Of course the permanent deformation is RELEVANT: that work enters the E equation. The bottom acts as a 'soft cushion', decelerating the ensemble more gently. It's no coincidence the OP used plastic party cups: they too deform easily. I'm not dismissing the role of fluid dynamics (straw man!), it's a different way of looking at things. I just wish you'd put a bit of 'meat on these bones', otherwise it's just talk and a waste of breath. | |
| Jun 29, 2020 at 16:42 | comment | added | Gert | @PhilipRoe Not that I know of. I plan to do it. | |
| Jun 29, 2020 at 16:21 | comment | added | Philip Roe | .It is claimed that this would not work with a tin cup. Did anyone try? | |
| Jun 29, 2020 at 14:28 | comment | added | Will | @Gert sorry, I skimmed over your notes about the bottom of the cup. It remains irrelevant unless you've repeated the experiment with a more robust cup that doesn't deform. I guarantee you still won't see one of those bounce elastically. And unless you can produce the phenomenon with an empty cup (besides the ball) or one filled with ice it would be rash to dismiss the role of fluid dynamics and an extrapolation from your observations to claim you've eliminated it. | |
| Jun 29, 2020 at 13:38 | comment | added | Gert | @Will were you able to observe any permanent deformation in the cup? As clearly stated, YES. In one instance the cup actually BROKE! I think you'd find that the fluid dynamics - in particular the dynamics of the air-water interface - are more important factors in explaining the transfers of energy in the experiment Not in line with my observations, I'm afraid. | |
| Jun 29, 2020 at 9:50 | comment | added | Will | @Gert were you able to observe any permanent deformation in the cup? I suspect not, and it isn't necessary to explain inelasticity in the collision. Kinetic energy is also lost to vibration, which would just as much affect a metal cup as a paper one, and indeed the cup is only a small fraction of the total mass of the system compared to the water so I think you'd find that the fluid dynamics - in particular the dynamics of the air-water interface - are more important factors in explaining the transfers of energy in the experiment (though these don't necessarily need explaining) | |
| S Jun 29, 2020 at 7:07 | history | suggested | Rasmus Faber | CC BY-SA 4.0 |
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| Jun 29, 2020 at 7:03 | review | Suggested edits | |||
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| Jun 29, 2020 at 6:21 | history | edited | Gert | CC BY-SA 4.0 |
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| Jun 29, 2020 at 4:52 | history | edited | Gert | CC BY-SA 4.0 |
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| Jun 29, 2020 at 4:45 | history | edited | Gert | CC BY-SA 4.0 |
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| Jun 29, 2020 at 4:38 | history | edited | Gert | CC BY-SA 4.0 |
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| Jun 29, 2020 at 4:22 | history | edited | Gert | CC BY-SA 4.0 |
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| Jun 28, 2020 at 23:36 | vote | accept | user6760 | ||
| Jun 28, 2020 at 16:59 | history | edited | Gert | CC BY-SA 4.0 |
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| Jun 28, 2020 at 16:52 | history | edited | Gert | CC BY-SA 4.0 |
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| Jun 28, 2020 at 5:04 | history | undeleted | Gert | ||
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| Jun 28, 2020 at 4:52 | history | deleted | Gert | via Vote | |
| Jun 28, 2020 at 4:36 | history | edited | Gert | CC BY-SA 4.0 |
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| Jun 28, 2020 at 4:28 | history | edited | Gert | CC BY-SA 4.0 |
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| Jun 28, 2020 at 4:20 | history | answered | Gert | CC BY-SA 4.0 |