Jump to content


Photo
* * * * * 1 votes

Where does the energy come from when two objects gravitate towards each other?


  • Please log in to reply
37 replies to this topic

#1 My Username

My Username

    Lepton

  • Members
  • 8 posts

Posted 24 January 2017 - 10:41 AM

I was thinking about this, and couldn't think of the answer.

 

Two objects far away from each other accelerate toward each other in space because gravity attracts them to each other. They come together to form one object. When the two objects were far apart, their combined energy was less than the newly formed object has. Where did that energy come from?


  • 0

#2 DrP

DrP

    Molecule

  • Senior Members
  • 2,109 posts
  • LocationUK

Posted 24 January 2017 - 10:47 AM

When they were far apart they had 'potential' energy. They come together to be in a lower state of energy which is more favourable. The potential energy is lost as kinetic energy when the objects mover together. When they crash/hit/land - the kinetic energy is converted to heat or sound as they crash into each other.  As far as I recall the total amount of energy is conserved.


Edited by DrP, 24 January 2017 - 10:47 AM.

  • 1

"Tonight I am going to party like it's on sale for $19.99"! - Apu Nahasapeemapetilon


#3 HallsofIvy

HallsofIvy

    Baryon

  • Senior Members
  • 362 posts

Posted 24 January 2017 - 01:29 PM

I was thinking about this, and couldn't think of the answer.

 

Two objects far away from each other accelerate toward each other in space because gravity attracts them to each other. They come together to form one object. When the two objects were far apart, their combined energy was less than the newly formed object has. Where did that energy come from?

 

  Your last statement, "When the two objects were far apart, their combined energy was less than the newly formed object has" is wrong.  As Dr. P said, you need to include "potential energy".


  • 0

#4 RiceAWay

RiceAWay

    Meson

  • Senior Members
  • 92 posts

Posted 24 January 2017 - 04:36 PM

In order to deal with "where does the energy come from" first you have to define what gravity is. And we do not understand it at all. All we can say is that gravity is a fundamental nature of matter.


Edited by RiceAWay, 24 January 2017 - 04:37 PM.

  • -1

#5 swansont

swansont

    Evil Liar (or so I'm told)

  • Moderators
  • 37,008 posts
  • LocationWashington DC region

Posted 24 January 2017 - 05:04 PM

In order to deal with "where does the energy come from" first you have to define what gravity is. And we do not understand it at all. All we can say is that gravity is a fundamental nature of matter.

 

 

I disagree. You just have to know how it behaves, and we do have an understanding of that.


  • 0

Minutus cantorum, minutus balorum, minutus carborata descendum pantorum          To go to the fortress of ultimate darkness, click the up arrow ^

I am not a minimum-wage government shill.             Forget it, Jake — it's Crackpottown.

My SFN blog: Swans on Tea                                                           

 

 

                                                                                                                     

 

 


#6 Strange

Strange

    SuperNerd

  • Senior Members
  • 13,256 posts
  • Location珈琲店

Posted 24 January 2017 - 06:59 PM

In order to deal with "where does the energy come from" first you have to define what gravity is. And we do not understand it at all. All we can say is that gravity is a fundamental nature of matter.


We understand gravity at least as well as any other fundamental property such as charge. Possibly better, because we can describe gravity in terms of a more fundamental thing (geometry).
  • 0

#7 antripathy

antripathy

    Lepton

  • Members
  • 5 posts

Posted 25 January 2017 - 03:18 PM

To know the reply it must be found out how they were separated in the first place.


  • 0

#8 RiceAWay

RiceAWay

    Meson

  • Senior Members
  • 92 posts

Posted 25 January 2017 - 06:46 PM

We understand gravity at least as well as any other fundamental property such as charge. Possibly better, because we can describe gravity in terms of a more fundamental thing (geometry).

WHAT is gravity. Don't cop out trying to tell us how it works. That's been around since Sir Isaac Newton.

 

Einstein described it as a curvature in space/time.

 

Can anyone suggest what is causing a curvature in space/time other than mass? So we're to believe that it's TIME that is causing gravity?


  • -2

#9 Mordred

Mordred

    Resident Expert

  • Resident Experts
  • 4,760 posts

Posted 25 January 2017 - 07:06 PM

Better question what is mass.

Definition "Resistance to inertia change" in other words its a kinenatic desciptive.

No time doesn't cause curvature either.

Spacetime curvature is a geometric system that maps freefall motion in accordance to geodesic Worldlines. Its a mathematical descriptive of relations. Not an entity unto itself.

http://www.sciencefo...-made-of/page-1

Energy is simply the "ability to perform work"

Stick to the physics definitions without trying to apply an entity quality to terms such as mass, energy, spacetime etc. They are properties

Edited by Mordred, 25 January 2017 - 07:19 PM.

  • 0
http://www.einsteins.../LightCone.html
http://cosmology101.wikidot.com/main
http://cosmocalc.wikidot.com/start
If you wish to change the rules, you must first understand the rules.

#10 Strange

Strange

    SuperNerd

  • Senior Members
  • 13,256 posts
  • Location珈琲店

Posted 25 January 2017 - 07:38 PM

WHAT is gravity.


What is electric charge?
  • 0

#11 My Username

My Username

    Lepton

  • Members
  • 8 posts

Posted 26 January 2017 - 12:12 AM

So then would the mass of the objects when apart include the potential energy? And would the mass of the objects be relative? I mean, if there were an observer traveling with each object, would they both come to the same conclusions about the mass of each object?


  • 1

#12 StringJunky

StringJunky

    Genius

  • Senior Members
  • 6,509 posts
  • LocationUK

Posted 26 January 2017 - 04:11 AM

WHAT is gravity. Don't cop out trying to tell us how it works. 

 

It is not the job of science to discuss ontology; it describes behaviour. Ontology is a philosophical subject.

 

 

 Ontology is the philosophical study of the nature of being, becoming, existence or reality as well as the basic categories of being and their relations. - wiki


  • 0

 Education, like life, is a journey not a destination


#13 Bender

Bender

    Protist

  • Senior Members
  • 781 posts

Posted 26 January 2017 - 10:29 AM

So then would the mass of the objects when apart include the potential energy? And would the mass of the objects be relative? I mean, if there were an observer traveling with each object, would they both come to the same conclusions about the mass of each object?

This is something I've been wondering about as well: can potential gravitational energy also be seen as mass, and if so, what is the reference? Moving them arbitrarily close together, the potential energy can become any arbitrarily large negative figure.


  • 1

#14 imatfaal

imatfaal

    lazy do-nothing mudslinger

  • Moderators
  • 7,747 posts
  • LocationSt James's Park

Posted 26 January 2017 - 12:50 PM

This is something I've been wondering about as well: can potential gravitational energy also be seen as mass, and if so, what is the reference? Moving them arbitrarily close together, the potential energy can become any arbitrarily large negative figure.

 

An Increase in GPE would only be seen as an increase in the energy of the system - and I guess would increase the inertia of the system; I would see this as an analogue of binding energy in the microscale 

 

On the second point - well I would hate to think how much energy it would take to separate two neutron stars in close binary orbit.  Obviously, your arbitrary distances cannot be totally arbitrary as we have universal limits of how much mass you can fit within a radius - and denser than that you have merging black holes. 


  • 0

A little learning is a dangerous thing; drink deep, or taste not the Pierian spring:
there shallow draughts intoxicate the brain, and drinking largely sobers us again.

- Alexander Pope

 

feel free to click the green arrow  ---->

 


#15 Bender

Bender

    Protist

  • Senior Members
  • 781 posts

Posted 26 January 2017 - 01:43 PM

So what is the actual radius of a black hole? If it is 0, then the GPE of the original matter would be infinite. Even if it is finite but still very small, the GPE of stars and galaxies could be larger than their actual mass (contributing even more to the GPE and so on). What am I missing?


  • 0

#16 RiceAWay

RiceAWay

    Meson

  • Senior Members
  • 92 posts

Posted 26 January 2017 - 07:39 PM

Better question what is mass.

Definition "Resistance to inertia change" in other words its a kinenatic desciptive.

No time doesn't cause curvature either.

Spacetime curvature is a geometric system that maps freefall motion in accordance to geodesic Worldlines. Its a mathematical descriptive of relations. Not an entity unto itself.

http://www.sciencefo...-made-of/page-1

Energy is simply the "ability to perform work"

Stick to the physics definitions without trying to apply an entity quality to terms such as mass, energy, spacetime etc. They are properties

We are in total agreement. But the question is "what is gravity" in particular. And to that we have no answer.


  • 0

#17 Delta1212

Delta1212

    Primate

  • Senior Members
  • 2,711 posts

Posted 26 January 2017 - 08:19 PM

We are in total agreement. But the question is "what is gravity" in particular. And to that we have no answer.


We don't have the answer to "what is X?" where X is anything fundamental. And we only have the answer to "What is Y?" where Y is anything else because we can describe Y in terms of a configuration of somethings or things X, which we don't have an answer to.

So, fundamentally, we don't know what anything is at all.
  • 1

#18 mistermack

mistermack

    Atom

  • Senior Members
  • 268 posts

Posted 26 January 2017 - 08:31 PM

Re the original question, if the two objects were connected by a stretched spring, then the kinetic energy that they gain as they are pulled together was potential energy, stored in the deformation of the spring, from it's natural shape.

 

If you think of spacetime as a form of spring, then a very similar process is happening. 


  • 0

#19 Mordred

Mordred

    Resident Expert

  • Resident Experts
  • 4,760 posts

Posted 26 January 2017 - 09:13 PM

We don't have the answer to "what is X?" where X is anything fundamental. And we only have the answer to "What is Y?" where Y is anything else because we can describe Y in terms of a configuration of somethings or things X, which we don't have an answer to.

So, fundamentally, we don't know what anything is at all.

Good answer not sure I could have said it better myself.

Lets look at another basic definition.

Potential energy: the energy possessed by a body by virtue of its position relative to others

So how many objects do you need to define potential energy?

Now think about that definition when the second objects undergoes kinetic motion. What happens to the potential energy in going towards or away from the other object?

Then equate that back to your conservation laws. Keep in mind the definition of energy. Ability to perform work forget fundamental just focus on the above definitions.

The answer everyone should arrive at is that energy doesn't need to come from anywhere. It is a consequence of relations between two or more objects/events/mass etc. This is precisely why energy is defined as a property. In order to define this property you need to define the system.

If you have no interaction between two objects/events etc energy=0 Potential or otherwise. Lol mass itself is an interaction.

Now lets take the above one step further mass and energy relations... both are literally due to interactions. In other words they are two properties describing interaction between two or more objects/events etc.

Now apply time.definition Rate of change or duration. So time isn't fundamental either but a property.

Lol how many forum threads did I just kill ? using nothing more than the Physics definitions?

Edited by Mordred, 26 January 2017 - 10:18 PM.

  • 1
http://www.einsteins.../LightCone.html
http://cosmology101.wikidot.com/main
http://cosmocalc.wikidot.com/start
If you wish to change the rules, you must first understand the rules.

#20 RiceAWay

RiceAWay

    Meson

  • Senior Members
  • 92 posts

Posted 27 January 2017 - 08:53 PM

We don't have the answer to "what is X?" where X is anything fundamental. And we only have the answer to "What is Y?" where Y is anything else because we can describe Y in terms of a configuration of somethings or things X, which we don't have an answer to.

So, fundamentally, we don't know what anything is at all.

We know what X does and so we can describe its effects on other things. But that does NOT define things like "gravity" or "electric charge". What IS it that makes an electron negative or a positron positively charged?

 

These are fundamental laws we cannot explain other than in terms of what they do.

 

And so you're close to the truth when you say that we know nothing about nothing at its base.


  • 0




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users