Timeline for Is speed conserved in bouncing from a rigid surface?
Current License: CC BY-SA 4.0
17 events
| when toggle format | what | by | license | comment | |
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| Nov 13 at 18:54 | answer | added | Peter - Reinstate Monica | timeline score: 1 | |
| Nov 13 at 16:09 | answer | added | dp4rker | timeline score: 0 | |
| Nov 13 at 15:41 | comment | added | Chris H | @zeynel this bounce would necessarily be silent. A real billiard ball's bounce isn't (that's where some of the energy goes). So it's not a model of real collisions. "All models are wrong, some are useful" applies to physics as well as to statistics, from where the quote comes. | |
| Nov 13 at 15:38 | comment | added | Chris H | @NuclearHoagie the perpetual motion machine you describe is known as the first kind. The third kind only has to maintain motion forever | |
| Nov 13 at 14:45 | comment | added | Nuclear Hoagie | @zeynel A perpetual motion machine isn't simply something that moves forever, it's a machine that can run forever while producing useful work - it's a limitless source of usable energy. There is nothing that prohibits perpetual motion without doing work - an object floating through deep space will indeed continue on the same trajectory with the same speed forever. No energy is extracted during a series of elastic collisions - even though it bounces forever, it's not a perpetual motion machine under the usual definition. | |
| Nov 13 at 14:14 | comment | added | Syntax Junkie | @zeynel: Got it! Thank you. I think the perpetual motion machine thought is a good one. Have the other answers already answered your question? If not, I will try to submit one that address the perpetual motion concern. But in the meantime, why is a perpetual motion machine not possible? Given conservation of energy--that energy cannnot be created nor destroyed, only changed in form--why is a perpetual motion machine impossible? Would the planets orbiting the sun for billions of years constitute close-to a perpetual motion machine? What about an idealized, frictionless pendulum? | |
| Nov 13 at 6:25 | comment | added | zeynel | @SyntaxJunkie Because if the ball does not slow down after elastic collision, it will keep moving forever because after each collision its speed will be the same. With this assumption you can build a perpetual motion machine. I believe as a fundamental assumption that perpetual motion machines are impossible. So the speed must decrease after each collision. | |
| Nov 13 at 0:11 | comment | added | Syntax Junkie | About this: "I don’t understand how the speed of the ball does not change after bouncing." It might help if you could explain why you expect the speed to change. | |
| Nov 12 at 16:35 | comment | added | Nuclear Hoagie | The single word "elastically" in the problem definition is doing some heavy lifting, indicating that kinetic energy is perfectly conserved before and after the collision. Everyday intuition about billiard balls slowing to a stop doesn't really apply here, as we've defined the system with ideal, unrealistic properties. | |
| Nov 12 at 15:32 | history | became hot network question | |||
| Nov 12 at 10:20 | history | edited | Qmechanic♦ |
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| Nov 12 at 9:18 | answer | added | Agnius Vasiliauskas | timeline score: 4 | |
| Nov 12 at 7:57 | answer | added | gandalf61 | timeline score: 7 | |
| Nov 12 at 7:44 | answer | added | Steeven | timeline score: 16 | |
| Nov 12 at 7:31 | comment | added | Ma Ye | here as a toy model, it assumes the collision is ideally elastic | |
| Nov 12 at 7:30 | review | Triage | |||
| Nov 12 at 7:35 | |||||
| Nov 12 at 7:29 | history | asked | zeynel | CC BY-SA 4.0 |