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A few simple questions

  1. Nov 16, 2006 #1
    Its been a looong time since i posted here... :uhh: but there have been a few nagging questions in mind that i needed clarified. And i would appriciate it if someone were nice enough to answer them... :smile:
    Anyway... here they are a few of them are very basic though..

    1)Consider a spacecraft in space or vaccum, would its mass matter there? as in would you require more force to accelerate a heavier rocket than one with lesser mass?

    2)If a mass is accelrated (hypothetically) with infinte energy.... does it gain infinte mass? and does its time stop? relative to the rest of us...( of course we won't be there cause it the mass will be infinte and there won't be any space for us... but anyway... :rolleyes: )

    3)If light has no mass but it has energy given by hf, taking energy and mass equilence, how did they prove that light had no mass?

    4)Is it wrong to equate newtonian mathematics with einstiens equations?

    5)Does a mass in vaccum or free space truly feel no resitance whatsoever?

    6)Does the energy of light reduce when it travels through long distances? If not... then why does red shift occur?

    7)No mass is allowed to travel beyond the speed of light... But does that apply to its relative velocity as well? as in is an objects relative velocity not allowed to exceed the speed of light? (i know the answer for this is no... its relative velocity doesn't matter here... but i just wanted to make sure....)

    8)Light travels at a constant velocity... but does it travel, can! it travel below the constant speed of light (in vaccum) i mean. Im not talking about the speeds in other mediums...

    9)Why is it that when a mass is accelarated towards the speed of light that it gains mass? i mean should it not lose mass so that it can travel at the speed of light massless... i know its because it follows the equations... but what is the theory backing it up?

    10)Could anyone let me know of some good books to read so that i can improve my knowledge in the fields of quantum theory, general and special relativity and string theory? I want books that go deep but not deep enough that a non physicst cannot understand.

    Thats it... if you reply to this... thx a lot... i really appriciate it... :smile: and thank you for your patience... :approve:
  2. jcsd
  3. Nov 16, 2006 #2


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    Staff: Mentor

    F=ma. Don't confuse weight and mass.
    Basically yes - and don't roll your eyes: Don't confuse mass and volume.
    Don't combine equations that don't match (just because the units match, doesn't mean the equations can be combined).
    That's not very specific, but generally yes.
    No. Again, don't confuse weight and mass. f=ma
    Yes, but its not the distance but the speed of the source.
    Since all velocity is relative, yes.
    Light travels at constant speed, not velocity.
    The equations are the theory. Others can give more detailed explanations of how it works, but "why" tends to head toward philosophy.
  4. Nov 16, 2006 #3


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    Staff Emeritus
    Science Advisor

    Why don't you read the sci.physics.faq about the two common (and different!) defintions of mass in common use in relativity


    and trim your questions down to just the single most important one (or perhaps a couple of closely related questions).

    As is, with so many questions (and so many assumptions on your part), I'm not sure where to start.
  5. Nov 16, 2006 #4
    k... cool will do... thx for the prompt replies though... :)
  6. Nov 16, 2006 #5
    k got it... most of the confusions gone... but....
    k... in general do objects feel any sort of resistance when travelling through vaccum irrespective of their mass... as in... is there any data that indicates that objects do tend to lose some energy when travelling long distances?

    k got it.... so what you mean is that redshift occurs because of the speed of the source and has nothing to do with its distance?

    k cool... so its relative velocity also must not exceed that of c, is that right? then what would happen if one photon comes in one direction and the another comes opposite to it... what would be the relative velocity that these two would see then? or is it erronous to compare light as an observer?

    Does this mean that with added energy to the object the space time around the object curves more than if it was at rest?

    and also does relativistic mass... add to its weight?

    thx for your patience guys... :smile:
  7. Nov 17, 2006 #6
    This is one thing that is quite easy to understand about relativity imo. "The speed of light appears constant to every inertial observer" is a postulate of relativity. This implies that for anyone moving without accelerations (e,g, a particle of light) that any particle of light appears to move with a speed c. Even if the observer is a photon moving at c and another photon is hurtling towards it at c from the opposite direction.

    If you want to know how to deal with the more general case of objects moving at any given velocity, you should look up the addition of velocities.
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