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Mass vs distance

  1. Feb 21, 2010 #1
    If all that was in a universe was a observer and a cube, would the mass of the cube only depend on the distance away it is from the observer? For example, if you are close to the cube it may look like it is very large, but from far away it would look like a point. With no other objects to use as a reference would that make the cube actaully change size? Is mass (like time) only relevant to the observer?
     
  2. jcsd
  3. Feb 21, 2010 #2

    Matterwave

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    Gold Member

    Well, if there wasn't even light...then the observer has no way of seeing this cube.
     
  4. Feb 21, 2010 #3
    Ok then, there is an abserver light and a cube.lol
     
  5. Feb 21, 2010 #4
    Provided the observer also has mass then the two would be accelerated towards each other at rates proportional to each other's masses.
     
  6. Feb 21, 2010 #5

    russ_watters

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    Staff: Mentor

    No, mass is not dependent on distance. What you are talking about is just angular size. Try this. Put your bathroom scale in front of a mirror. Measure your weight. Move it back away from the mirror and measure your weight again. Did it change?
     
  7. Feb 21, 2010 #6
    mass is independent of the gravitational field (potential) ; but WEIGHT decreases as that cube is removed from an observer since their gravitational attraction decreases....

    So that cube would have one weight on the moon, another weight here on earth, but it's mass remains fixed in stationary positions. (it might be considered to change relativistic mass with speed, but that's in Einstein's relativity when things go real fast.)

    also, the mass of an object is not specificallty related to its size...it's physical dimension..In other words a cube of iron of a fixed size has more mass than a cube of air of the same size...becauses it's constitutent atoms have more mass....due to more neutrons/protons and so forth...
     
  8. Feb 22, 2010 #7
    Can you picture the dimensions of the solar system?

    Probably not, for they are of an order so amazing that it is difficult either to realize or to show them.

    You may have seen a diagram of the Sun and planets, in a book. Or you may have seen a revolving model of the kind called an orrery (because the first was built for an Earl of Orrery in 1715). But even the largest of such models--such as those that cover the ceilings of the Hayden Planetarium in New York and the Morehead Planetarium at Chapel Hill-are far too small. They omit the three outermost planets, yet still cannot show the remaining ones far enough apart.

    The fact is that the planets are mighty small and the distances between them are almost ridiculously large. To make any representation whose scale is true for the planets sizes and distances, we must go outdoors.

    The following exercise could be called a Model, a Walk or a Happening. I have done it more than twenty times with groups of varied ages (once we were televised) or with a single friend; and others, such as elementary-school teachers, have carried it out with these instructions. Since it is simple, it may seem suitable for children only. It can, indeed, be done with children down to the age of seven. Yet it can also be done with a class consisting of professors of astronomy. It will not waste their time. They will discover that what they thought they knew, they now apprehend. To take another extreme, the most uncontrollable high-school students or the most blase college students unfailingly switch on their full attention after the first few paces of the excursion.

    There is one other party that may profitably take the planet-walk, and that is yourself, alone. Reading the following description is no substitute: you must go out and take the steps and look at the distances, if the awe is to set in.

    First, collect the objects you need. They are:

    Sun-any ball, diameter 8.00 inches
    Mercury-a pinhead, diameter 0.03 inch
    Venus-a peppercorn, diameter 0.08 inch
    Earth-a second peppercorn
    Mars-a second pinhead
    Jupiter-a chestnut or a pecan, diameter 0.90 inch
    Saturn-a hazelnut or an acorn, diameter 0.70 inch
    Uranus-a peanut or coffeebean, diameter 0.30 inch
    Neptune-a second peanut or coffeebean
    Pluto- a third pinhead (or smaller, since Pluto is the smallest planet)

    _______________________________
    mercury mountaineer wheel hub bearing
    mitsubishi shogun cars
     
  9. Feb 22, 2010 #8
    I am just trying to comprehend was size and mass is. For us as humans we see the universe as very large, and things like atoms as very small. But this is only the case for something of our size. To a single cell organism a atom and the universe is much larger. if there was a observer with a mass much larger than ours would he not see the universe as a lot smaller. Our perception of mass is just that, our perception. So a cube can be any size that we wish to make it. If we can say time is only relevant to the observer why can't mass, size, volume, distance, everything for that matter only be relevant to an observer?
     
  10. Feb 22, 2010 #9

    uart

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    Hi binbots, I think this video explains the situation fairly well.

    "Father Ted - Small versus Far Away" see :

    Hope that helps. :tongue:
     
    Last edited by a moderator: Sep 25, 2014
  11. Feb 22, 2010 #10
    technically speaking, size and mass (volume is size, and distance is irrelevant) are both relativistic quantities. So they are both relative to time, and time is relative to speed. So as the speed of the cube approaches light speed, its mass approaches infinity, and its size approaches zero. heck, even distance is relativistic, although I still believe irrelevant in this sense. So i think everything is pretty much relative to a speed, which is relative to an observer. take what you want from that.]

    cheers
     
  12. Feb 22, 2010 #11
    Thanks for the Father Ted video. I love that show. It is true though that things like distance and size have to be tought to us and some point.
     
  13. Feb 22, 2010 #12
    Q1 the mass would not change its state in relation to the focal point.

    Q2the mass would change size in relation to the focal point, but without tools to measure the distance a calculable measurement would be improbable.

    Q3 yes, But to clarify this question. Its existence is, ref from Q1. So the observer seeing it or not does not affect its state of existing. The appearance of the object does change in relation to distance trajectory and velocity. So if the observer does not look at the cube will it even exist? Like time if the observer does not have a watch will time exist?
     
  14. Feb 22, 2010 #13


    Q1 the mass would not change its state in relation to the focal point.

    Q2the mass would change size in relation to the focal point, but without tools to measure the distance a calculable measurement would be improbable.

    Q3 yes, But to clarify this question. Its existence is, ref from Q1. So the observer seeing it or not does not affect its state of existing. The appearance of the object does change in relation to distance trajectory and velocity. So if the observer does not look at the cube will it even exist? Like time if the observer does not have a watch will time exist?
     
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