Timeline for If Earth starts moving when attracted by an object, where does the energy come from?
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| Jun 4, 2020 at 16:03 | history | edited | CommunityBot |
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| Sep 17, 2015 at 10:56 | comment | added | anna v | If I have a weight hanging from a spring I have a harmonic oscillator to start with, weight will be oscillating until dissipation stops the oscillations because it eats up the energy available: heat of the spring . So the weight will come at rest,the spring stretched up to a certain point. This stretching is used in old fashioned spring weight measurements except the spring is chosen with appropriate coefficients to stop the oscillation. ( high dissipation ) | |
| Sep 17, 2015 at 10:19 | comment | added | user36790 | ...why I'm telling that restoring force is not the reactive force, check this. So, when the spring provides the reactive force, why doesn't the block upward then? I know I am really confusing something. Can you please clear away my confusion?? BTW, I have to consider the wall also to which the spring is attached in order to consider the conservation of momentum. Thanks in advance & again pardon for bothering you:) | |
| Sep 17, 2015 at 10:14 | comment | added | user36790 | First I apologise to contact you from this thread after over a year. But if you help me clearing some problem, I would be grateful. Let a spring be fixed at one end & a block is attached at the other end(vertical configuration under gravity). The block would provide a force $mg$ on the spring & it would get stretched till the restoring force balances $mg$. However, restoring force is not the reactive force due to third law; as the block imparts $mg$ on the spring downward, spring must provide a restoring force on the block upward. Now , my question is: does the block move up? ... | |
| Oct 25, 2014 at 6:46 | comment | added | anna v | i said they will bang on each other, earth and rocket, after the zero momentum is reached and the energy is fully potential, they will fall on each other. | |
| Oct 25, 2014 at 5:25 | comment | added | user36790 | ...So to move with acceleration, the huge force should be imparted continuously so that part of it works against the earth's gravity which will be stored as PE & the rest force will accelerate it to the escape velocity... | |
| Oct 25, 2014 at 5:21 | comment | added | user36790 | My thinking: To accelerate the rocket at first, huge force much greater than gravitation is needed,which is gained from the explosion. But if there were no force after that, they will decelerate and then will accelerate towards each other like the tomato.... | |
| Oct 24, 2014 at 12:11 | comment | added | anna v | have you checked en.wikipedia.org/wiki/Conservative_force . the answers you have got are on those lines. | |
| Oct 24, 2014 at 10:33 | comment | added | anna v | yes, that is a correct summary | |
| Oct 24, 2014 at 8:51 | comment | added | user36790 | Great answer! When the tomato is thrown up, it accelerates momentarily and gains KE from the energy of the thrower. By conservation of momentum & Newton's third law, the thrower-&-earth will accelerate momentarily using the internal energy of the thrower. But due to mutual gravitation, they decelerate & ultimately come to a halt. Their KE thus is converted to PE . When they accelerate towards each other, their PE is converted tn PE. Thus it is all the energy of the thrower. Energy and momentum thus are conserved,right? | |
| Oct 24, 2014 at 4:16 | vote | accept | CommunityBot | moved from User.Id=36790 by developer User.Id=2911 | |
| Oct 23, 2014 at 5:09 | history | edited | anna v | CC BY-SA 3.0 |
clarification after comment
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| Oct 23, 2014 at 5:00 | comment | added | anna v | exactly the same thing, you provide the energy with the impulse of the throw , taken from the breaking of chemical bonds in the matter that makes you up, and ultimately from the heat of sun that makes things grow that you eat and have available energy. Again, you-and-the-earth initially accelerate downwards and the tomato upwards: from momentum conservation the available energy is shared. (it is the huge mass of the earth that is confusing you, very little motion is needed to give the same momentum as to the tomato). | |
| Oct 23, 2014 at 1:12 | comment | added | user36790 | Sir, if I take a tomato in place of the rocket? When a tomato is thrown upwards,what will happen then? There is no explosion now! | |
| Oct 22, 2014 at 19:38 | history | answered | anna v | CC BY-SA 3.0 |