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Is it possible to define motion

  1. Jan 13, 2006 #1
    Is it possible to define motion--to give it some definition as an the independent concept (if not phenomenon) that it is (in other words, to give "motion" a definition apart from just "change in position over time")? If it is, what are your thoughts on what that definition would be?
  2. jcsd
  3. Jan 13, 2006 #2
    I think you can at least simplify "change of position over time" to just "change of position" because if something has changed then necessarily some time has passed. The "over time" part is an indicator of speed, a characteristic of motion but not exactly motion per se.
  4. Jan 14, 2006 #3
    You can't have motion without anything moving, so no I don't think there can be an independent phenomenon.

    Also Orefa I don't agree that time needs to pass for something to move.
    Or better, we don't know that it has to pass for things to move.
  5. Jan 14, 2006 #4
    Isn't this simply a matter of definition? Since motion is a change of position then two or more different positions must be involved. If time does not pass then all relevant positions are involved at the same time, which is not motion but omnipresence.
  6. Jan 15, 2006 #5


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    Sikz, it is possible to define any word you wish in any manner so long as you can get some group of people to agree to use the word in that manner. I can't figure out what you think the philosophical significance of this is, however. Do you simply want to deduce the consequences of how other speech acts would change if the entire English-speaking population of the world chose to speak of motion as being something other than "change in position?" Or are you really asking a philosophy of language questions, such as 'Is it possible to define an abstract intrinsically, without reference to other abstractions?' If the latter, I don't see any way how.

    There are foundational consequences for this, in that any language becomes circular in a sense, without any provable grounding aside from implied agreement. Are these what you wish to explore? Realist v. social constructivist notions of word reference?
  7. Jan 15, 2006 #6
    It isn't linguistics that I'm attempting to explore, but the idea of motion in general. It seems that physics is largely built upon the study of motion--really, every interaction can be explained in terms of motion and energy is only detectable when it becomes a form of motion (be it the vibrations of temperature, linear motion, acceleration, etc). This struck my interest, but motion is just "change in position over time"; as it is such a central and fundamental concept, I wondered if there might not be some other way of understanding it.
  8. Jan 15, 2006 #7
    Motion is fundamental because it reflects change, and change is fundamental to existence. Since the universe exists, changes happen. (I've just had a short related discussion in https://www.physicsforums.com/showthread.php?t=106688".)

    It also appears that all changes involve position in some way. We don't see a change of mass or a change of electric charge by itself, these are always accompanied by something that changes position. It may be simply the fact that space is equally fundamental as change: both are basic universal properties.
    Last edited by a moderator: Apr 21, 2017
  9. Jan 15, 2006 #8
    If all changes involve position, and motion is "change in position over time" (or anything involving position and change), couldn't motion be seen as more fundamental than change?

    In which case, it would make no sense to say that motion reflects change; change would, rather, reflect motion.
  10. Jan 15, 2006 #9
    If we knew for a fact that all changes must necessarily involve position then maybe. But I don't know this for a fact, I only said that it appears to be so. No proof. For now, if something can change mass and something can change electric charge and something can also change position then personally I find that change itself is a more fundamental concept than change of position specifically.
  11. Jan 15, 2006 #10
    can we say, since change occurs over time, that there must be some effect in space, as well? after all time is not seperate from space.
    if it turns out that we can say this about "change", then it also turns out that "change" is "motion". then, we are left with an equivalence of "motion" and "change". further, it would mean that all "change" occurs, in physicality, expressed as "motion," and that "change" is, also, an expression of "motion."

    but we must remember that all "change" and all "motion" are relative changes; that one "thing" changes only in relation to some other "thing". this is to say that there are no "independent motions" or "independent changes". "change" and "motion" depend on a context of relative relationships.
  12. Jan 15, 2006 #11
    I don't know. Can we? Based on what rationale?

    Nothing is separate from anything else, yet space is measured in meters, mass is measured in kilograms and time is measured in seconds. These are all different things. Must a change of position be accompanied by a change of mass? Or must a change of mass be accompanied by a change of position? Why or why not? If there is a rationale necessity for all changes to at least involve a change in space then we may be able to equate change with motion. Short of this, I don't see how we can call them equivalent.
  13. Jan 15, 2006 #12
    because time and space are a unity, fundamentally, it follows that any effect in time is an effect in space and vice-versa.
    the main point is that: there is motion, so long as there is a spatial effect. so long as change in mass produces a change in/of space, there is an effect, both, in and of time.
    motion in time, it seems, is equivalent to change in space; when there's one, there's the other.
  14. Jan 15, 2006 #13
    This was very confusing, sorry.
    As in the same thing? I would disagree.

    If so then we are using two different words to represent the same thing and we should get rid of one redundant term. But I don't think time and space are the same thing.

    I loosely agree with this part by loose definition of motion.

    When you speak of an effect in and of time, do you just mean that time passes?

    This is not clear. How do you measure "motion in time"? I understand that "change in space" is just motion. But then "motion in time" would become "change in space in time" and that doesn't work.
  15. Jan 16, 2006 #14
    you have not read what i posted. i think that you have looked at it with the intent to disagree, but did not really consider what i posted.
    "an effect in time" means that the effect occurred in time, and that it is "of time" means that time is altered by its occurring. this latter point is a little harder to harder to understand, because the ffect is small, but it is, nonetheless, logically true.
    what is wrong with saying that something took place "in time in space"? this is really the only logically conclusion. if something takes place in time it must take place in space and vice versa.

    i am not trying to argue for arguments sake. that is not my style. i am talking logistics here. but you must try to understand what i say without taking my words as syntax and then argue along those lines. (of syntax).

    time and space are a unity. this is no speculation or anything. this is fact. we call it space-time for a reason. you know? that is because they are unified. affections of space are affections of time, and vice versa. period.

    the concepts of time and space are unified and so are motion and change.

    this could not have been expressed any clearer. just because it is not easily understood, does not mean that it isn't so.

    please try to understand what isay, without just arguing back at me, and see if what i am saying is so. it is and i have no doubt of this.

    please just listen with the intent to understand... that is all.
  16. Jan 16, 2006 #15
    is motion, then, just a change in position? or is motion any effect that occurs in time? if it occurs in time then it must be a movement of some kind. it is kind of crazy to think of it otherwise. no?
  17. Jan 16, 2006 #16
    if we want to understand, fully, we must listen to what each other says, as though it is true... after contemplating the proposal we then come to understand the faults with it. i am certain that many here are not really reading what is in front of them, as though it was meaningful or remotely true.

    there is a lot of arguing, but not many are listening... to each other.

    please. i ask kindly. nothing will benefit anyone if we arent open. please open to each other. listen. please!
  18. Jan 16, 2006 #17
    A speaker must be intelligible to his audience. Those who pay him the courtesy of listening should not be disparaged if they fail to unravel the message. They'll just walk away.
  19. Jan 17, 2006 #18
    correct me if i am wrong, but the fact that 'time' and 'space' must be conceived of as a unity (known as 'time-space'), is to say that an affect in one is an affect in the other, meaning that they exist, fundamentally, in a dynamic and unified relationship, through and through.
  20. Jan 17, 2006 #19


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    Sorry, guys, but it doesn't look like anything is going to come from this.
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