Thread: Re: [Algorithms] rather curious (Page 2)
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From: Favnir <fa...@wi...> - 2000-09-11 16:52:19
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Sorry to rush in, but I think that's exactly what he's saying... A bullet dropped on the ground will hardly produce any dent at all. As for one shot from a gun's barrel...well, I leave it to your = imagination ;-) Are, F ----- Original Message -----=20 From: Steven Clynes=20 To: gda...@li...=20 Sent: Monday, September 11, 2000 5:59 PM Subject: Re: [Algorithms] rather curious [SNIP] Or are you saying the cause of the dent is momentum, not force? Just rambling, Steve |
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From: Akbar A. <sye...@ea...> - 2000-09-11 17:34:45
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>A bullet dropped on the ground will hardly produce any dent at all. yes, because F is so low. if the accelration has increased (we can change this <weapon>) F will increase cause the way the ecquation works it self out. F = ma so the greater F is, the stronger/deeper it will be (the dent in earth). for ex. andre in his book gives a parrelation of a pea being stronger than a truck. you just alter the values of the equations and in some cases you will get F in the pea case to be larger than the truck case. i'm sure ron will bring up more cases in this but, this is the general jist of it. still waiting on my GR book's... got next day for the einsteins, and hawkings for 2 day delievery ;) peace, akbar A. -----Original Message----- From: gda...@li... [mailto:gda...@li...]On Behalf Of Favnir Sent: Monday, September 11, 2000 12:51 PM To: gda...@li... Subject: Re: [Algorithms] rather curious Sorry to rush in, but I think that's exactly what he's saying... A bullet dropped on the ground will hardly produce any dent at all. As for one shot from a gun's barrel...well, I leave it to your imagination ;-) Are, F ----- Original Message ----- From: Steven Clynes To: gda...@li... Sent: Monday, September 11, 2000 5:59 PM Subject: Re: [Algorithms] rather curious [SNIP] Or are you saying the cause of the dent is momentum, not force? Just rambling, Steve |
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From: Favnir <fa...@wi...> - 2000-09-11 19:53:10
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LOL!... Which "F" will that be? For what I make out of your argument, the "acceleration" you are talking about must be the one upon impact, but what comes before that is, momentum. Are, F ----- Original Message -----=20 From: Akbar A.=20 To: gda...@li...=20 Sent: Monday, September 11, 2000 7:31 PM Subject: RE: [Algorithms] rather curious >A bullet dropped on the ground will hardly produce any dent at all. yes, because F is so low. if the accelration has increased (we can change this <weapon>) F will increase cause the way the ecquation works it self out. F =3D ma so the greater F is, the stronger/deeper it will be (the dent in = earth). for ex. andre in his book gives a parrelation of a pea being stronger = than a truck. you just alter the values of the equations and in some cases = you will get F in the pea case to be larger than the truck case. i'm sure ron will bring up more cases in this but, this is the general = jist of it. still waiting on my GR book's... got next day for the einsteins, and hawkings for 2 day delievery ;) peace, akbar A. -----Original Message----- From: gda...@li... [mailto:gda...@li...]On Behalf Of = Favnir Sent: Monday, September 11, 2000 12:51 PM To: gda...@li... Subject: Re: [Algorithms] rather curious Sorry to rush in, but I think that's exactly what he's saying... A bullet dropped on the ground will hardly produce any dent at all. As for one shot from a gun's barrel...well, I leave it to your = imagination ;-) Are, F ----- Original Message ----- From: Steven Clynes To: gda...@li... Sent: Monday, September 11, 2000 5:59 PM Subject: Re: [Algorithms] rather curious [SNIP] Or are you saying the cause of the dent is momentum, not force? Just rambling, Steve _______________________________________________ GDAlgorithms-list mailing list GDA...@li... http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list |
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From: Akbar A. <sye...@ea...> - 2000-09-11 21:36:30
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please stop with this html mail !! it is worse than bright green ;) >Which "F" will that be? yes, i admit i did state that wrong, i should have said something like; if you jack up the velocity, like in the case of the bullet the momentum will be much more powerful. so when it hits the ground there is a lot of force against the surface of the earth. since there is a lot of force, we get a larger dent. peace, akbar A. -----Original Message----- From: gda...@li... [mailto:gda...@li...]On Behalf Of Favnir Sent: Monday, September 11, 2000 3:52 PM To: gda...@li... Subject: Re: [Algorithms] rather curious LOL!... Which "F" will that be? For what I make out of your argument, the "acceleration" you are talking about must be the one upon impact, but what comes before that is, momentum. Are, F ----- Original Message ----- From: Akbar A. To: gda...@li... Sent: Monday, September 11, 2000 7:31 PM Subject: RE: [Algorithms] rather curious >A bullet dropped on the ground will hardly produce any dent at all. yes, because F is so low. if the accelration has increased (we can change this <weapon>) F will increase cause the way the ecquation works it self out. F = ma so the greater F is, the stronger/deeper it will be (the dent in earth). for ex. andre in his book gives a parrelation of a pea being stronger than a truck. you just alter the values of the equations and in some cases you will get F in the pea case to be larger than the truck case. i'm sure ron will bring up more cases in this but, this is the general jist of it. still waiting on my GR book's... got next day for the einsteins, and hawkings for 2 day delievery ;) peace, akbar A. -----Original Message----- From: gda...@li... [mailto:gda...@li...]On Behalf Of Favnir Sent: Monday, September 11, 2000 12:51 PM To: gda...@li... Subject: Re: [Algorithms] rather curious Sorry to rush in, but I think that's exactly what he's saying... A bullet dropped on the ground will hardly produce any dent at all. As for one shot from a gun's barrel...well, I leave it to your imagination ;-) Are, F ----- Original Message ----- From: Steven Clynes To: gda...@li... Sent: Monday, September 11, 2000 5:59 PM Subject: Re: [Algorithms] rather curious [SNIP] Or are you saying the cause of the dent is momentum, not force? Just rambling, Steve _______________________________________________ GDAlgorithms-list mailing list GDA...@li... http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list |
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From: <ro...@do...> - 2000-09-11 16:53:19
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Steven Clynes wrote: >Ron Levine wrote: >> >> >.... >> >So you can see that a body of any mass will hit the earth at the same time. >> >The difference due to the original gravitation law is that a more massive body >> > will hit the earth with more FORCE and make a bigger dent. >> > >> >> Here, I think your use of "FORCE" is not appropriate. The two bodies >> fall under the same acceleration, so fall for the same time duration >> and hit the earth with the same speed, but the more massive body has >> more kinetic energy and more momentum, so makes a bigger dent. > >But I thought (possibly naively), that by definition Force = Mass * >Accelleration, hence more mass, more force (for a fixed accelleration, >ie gravity). > >Or are you saying the cause of the dent is momentum, not force? > The cause of the dent is dissipation of energy. The body had non-zero momentum before the collision and (assuming no bounce but entirely dissipative energy loss) zero momentum after the collision. The change in momentum, in the classical picture, is the integral of F dt, where t is time, integrated over the time of the collision (usually short). Force x time is called _impulse_. In a collision the time is very short, and the force varies sharply over this short time period, and we usually do not know the force as a function of time in this short interval, nor even the length of the interval, so we can only deal with the impulse, which we know exactly as the change in momentum. Note that this "force" under discussion at this point is NOT gravitational force, but rather the contact force between the body and the earth--actually it is in the class of electromagnetic interaction, not gravitational. |
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From: Pierre T. <p.t...@wa...> - 2000-09-10 21:33:15
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A quick post to tell Flexporter users there's a new version (1.05) here: www.codercorner.com/Flexporter.htm With some code to read ZCB files, support for compressed files, an option to fix non-manifold meshes, among other little things. Pierre |
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From: Jeff L. <je...@di...> - 2000-09-10 23:38:52
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The reason people don't know a lot about relativistic physics is they have trouble with Galileo let alone Einstein. Funny this should come up today since last night we got into a little debate about this at dinner with some friends. My friend works at JPL and we were talking about skydiving and this came up. No one believed us that the objects hit at basically the same time regardless of mass. So we all started dropping stuff on the table to prove it. Pretty funny. It is always amazing how a simple "try it yourself" can surprise people. In general they just believe it should be some way and never check it out. No wonder Galileo ended up in jail. The whole what is gravity thing is pretty tough. Claiming to have the "right" answer is probably folly. Clearly Galileo/Newton works fine for most applications any human would run into. I am no expert on gravitational physics but from what I know, common thinking is based on Einstein's theory of General relativity. The mass of objects warp spacetime and the falling is explained by objects following a straight path in space-time. Galileo went to great pains to prove that Aristotle and Plato were wrong about falling objects. If he wasn't exactly right to the order of 10^-24 or whatever, I am not sure it matters. At JPL, good old Newton does the job for most things. Using Newton's equations for the force of gravity and f=ma you can see how the mass of the falling object just drops out. Different masses do cause the objects to hit with different forces but that is different from the time, eh. If someone wants to implement actual relativistic physics for simple rigid body simulations, I am sure it would be cool, but Newton is good enough for me :) Didn't they do the feather and rock demo on an Apollo mission as a pr thing? I seem to remember seeing a video of it. -Jeff At 04:26 PM 9/10/2000 -0500, you wrote: >hey, >i am just wondering, but how many people know about *this* >"gravity isn't really a force" and that it is caused by the curvature in the >space time fabric. > >And, if you drop two objects in a vacuum they *really* don't fall >at the same rate (difference is very small, order of 10^-24) <this *makes >sense*> >why don't more people know this? > >even if it's at a difference 10^-24, >i assure you, if we had money that was this accurate, banks would "require" >this much precision in there software :| > >i am just curious what is the *the few on this list* knowledge about >this... > >i recently (3 minutes ago) got in an argument with a friend on this *topic*, >he told me his professor said that "Gravity is a FORCE" and saying anything >different from that is pure anarchy. > >i told him what is above is true and André Lamothe writes this in all of his >books, and i'm pretty sure he knows more than your professor (the laws make >sense as well), ... > > > >i am probably just t-ed of cause i didn't have more proof about the space >time fabric one :| > > >btw, andre, if your not on the list; >i highly suggest you join :) i know your busy with volume 2 and all... > >peace, >akbar A. > > >_______________________________________________ >GDAlgorithms-list mailing list >GDA...@li... >http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list |
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From: Akbar A. <sye...@ea...> - 2000-09-11 01:51:49
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>The reason people don't know a lot about relativistic physics is they have >trouble with Galileo let alone Einstein. i don't want to sound stupid (being that i have not had *any* experience with Einstein's work) but wasn't most of his stuff, derived from material which was pretty trivial? >No one believed us that the objects hit at basically the same time regardless >of mass. So we all started dropping stuff on the table to prove it. >Pretty funny. been there, done that :) well you can always look at it and explain to other people that' it's a formula and you are just putting in data which has a very *large* gap. the precision is small but the difference is *still* there, so in all of it's actuality they *don't* fall at the same rate :) just cause we can't see it, doesn't mean it doesn't exsist ;) imho, it must of been a pain in the ass to convince people that we/objects are "attracted" to each other ;) >The whole what is gravity thing is pretty tough. Claiming to have the >"right" answer is probably folly. aren't researchers still clamoring about a "true/right way" to describe light and all it's properties; "wait a second it's a wave, oh No it's a particle!" (i will stop this, i'm going on a tangent ;) <grin> >Using Newton's equations for the force of gravity and f=ma the mind is so weird. maybe i saw this in a dream or something but wasn't it first published as -f = -ma ? >Didn't they do the feather and rock demo on an Apollo mission as a pr thing? >I seem to remember seeing a video of it. do we even have video capture devices that are that accurate to get the 10^-24 precision, so we could "see" the diff? anyways, i think i got some reading to do about this topic so i can argue with a better foot hold. i hope this book does the trick, just put the order in. http://www.amazon.com/exec/obidos/ASIN/0517029618/o/qid=968634459/sr=2-1/102 -7947677-2983366 peace, akbar A. being in the game biz, we actually *apply* all these fancy equations most people just memorize for the midterm and forget about. -----Original Message----- From: gda...@li... [mailto:gda...@li...]On Behalf Of Jeff Lander Sent: Sunday, September 10, 2000 6:37 PM To: gda...@li... Subject: Re: [Algorithms] rather curious The reason people don't know a lot about relativistic physics is they have trouble with Galileo let alone Einstein. Funny this should come up today since last night we got into a little debate about this at dinner with some friends. My friend works at JPL and we were talking about skydiving and this came up. No one believed us that the objects hit at basically the same time regardless of mass. So we all started dropping stuff on the table to prove it. Pretty funny. It is always amazing how a simple "try it yourself" can surprise people. In general they just believe it should be some way and never check it out. No wonder Galileo ended up in jail. The whole what is gravity thing is pretty tough. Claiming to have the "right" answer is probably folly. Clearly Galileo/Newton works fine for most applications any human would run into. I am no expert on gravitational physics but from what I know, common thinking is based on Einstein's theory of General relativity. The mass of objects warp spacetime and the falling is explained by objects following a straight path in space-time. Galileo went to great pains to prove that Aristotle and Plato were wrong about falling objects. If he wasn't exactly right to the order of 10^-24 or whatever, I am not sure it matters. At JPL, good old Newton does the job for most things. Using Newton's equations for the force of gravity and f=ma you can see how the mass of the falling object just drops out. Different masses do cause the objects to hit with different forces but that is different from the time, eh. If someone wants to implement actual relativistic physics for simple rigid body simulations, I am sure it would be cool, but Newton is good enough for me :) Didn't they do the feather and rock demo on an Apollo mission as a pr thing? I seem to remember seeing a video of it. -Jeff At 04:26 PM 9/10/2000 -0500, you wrote: >hey, >i am just wondering, but how many people know about *this* >"gravity isn't really a force" and that it is caused by the curvature in the >space time fabric. > >And, if you drop two objects in a vacuum they *really* don't fall >at the same rate (difference is very small, order of 10^-24) <this *makes >sense*> >why don't more people know this? > >even if it's at a difference 10^-24, >i assure you, if we had money that was this accurate, banks would "require" >this much precision in there software :| > >i am just curious what is the *the few on this list* knowledge about >this... > >i recently (3 minutes ago) got in an argument with a friend on this *topic*, >he told me his professor said that "Gravity is a FORCE" and saying anything >different from that is pure anarchy. > >i told him what is above is true and André Lamothe writes this in all of his >books, and i'm pretty sure he knows more than your professor (the laws make >sense as well), ... > > > >i am probably just t-ed of cause i didn't have more proof about the space >time fabric one :| > > >btw, andre, if your not on the list; >i highly suggest you join :) i know your busy with volume 2 and all... > >peace, >akbar A. > > >_______________________________________________ >GDAlgorithms-list mailing list >GDA...@li... >http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list _______________________________________________ GDAlgorithms-list mailing list GDA...@li... http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list |
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From: <ro...@do...> - 2000-09-11 03:54:19
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Jeff Lander wrote > At JPL, good old Newton does the job for most things. I'm sure that this is true for _most_ things at JPL, certainly for all the work they do on dynamics of Earth-launched space craft and their motion within the solar system. But not all things. I think that at JPL there are probably also astronomers who are involved in observing such things as the cosmic evidence for gravitational lenses (see the spectacular photos published just last yea--I'm not sure where, but I saw them on the NY Times Science pages) and evidence for black holes at the centers of galaxies, and these are definitely General Relativistic phenomena, explainable only in the context of space-time curvature. |
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From: <SHA...@ao...> - 2000-09-10 07:53:48
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In a message dated 09/09/00 15:56:29 !!!First Boot!!!, zi...@n-... writes: << By just getting the height under the player you will often run into trouble with stairs where you will just kind of pop up and it looks/feels quite bad. >> True, but what I do with stairs is make the player jump just a little like you would if you were running up stairs. I just compute how much higher the next surface is and then give the player some negative gravity :) to bounce them up into the air. John. |
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From: Jason Z. <zi...@n-...> - 2000-09-08 15:31:51
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Sorry for being dull, but I don't get it. :) Could you go into a bit more detail? I've tried remembering the velocity from last frame and doing tests against that to stop the oscillating but every time I did that it also cancelled out some movement I did want. Thanks, - Jason Zisk - nFusion Interactive LLC ----- Original Message ----- From: <SHA...@ao...> To: <gda...@li...> Sent: Friday, September 08, 2000 9:19 AM Subject: Re: [Algorithms] Simple player collision response problem > In a message dated 07/09/00 17:15:05 !!!First Boot!!!, zi...@n-... > writes: > > << > What I'm doing now is simply calculating a sliding plane based on the poly > the player is hitting and sliding him along that with the remaining velocity > after the initial collision. I do this recursively each frame against the > environment until the velocity is so small I can just set it to zero. > >> > > Hi, > > What you need to do is do it recursively between frames not each frame > otherwise you will see these oscillations. > > John. > _______________________________________________ > GDAlgorithms-list mailing list > GDA...@li... > http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list |
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