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I have demonstrated that weight only is measured based on the gravitational pull of where you live.

For example, the gravity on the surface of Mars is three times smaller than the gravity on the surface of Earth.

So my question is simple: If we take into account that weight is only measured based on gravitational pull on that mass, if there was no gravity how would we define mass?

That is, would mass weigh anything if no gravitational pull acted on it? Then what would be mass?

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    $\begingroup$ The gravity in Mars is a three times smaller compared to Earth's gravity. And have you heard of $F=ma$? $\endgroup$
    – jinawee
    Oct 19, 2013 at 19:31
  • $\begingroup$ So what would act on the force if there was no gravity? Not making much sense! And Mars has less gravity because is smaller? I thought if it closer to Sun it have stronger gravity! $\endgroup$
    – Strong
    Oct 19, 2013 at 19:32
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    $\begingroup$ Have you studied Hooke's law, you could measure mass as: $m=kx/a$. $\endgroup$
    – jinawee
    Oct 19, 2013 at 19:37
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    $\begingroup$ Mars is further from the sun than earth.... $\endgroup$
    – Kyle Kanos
    Oct 19, 2013 at 19:50
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    $\begingroup$ I think this is actually a reasonable question. Just because the distinction is obvious to people who have a Physics background doesn't mean it isn't to everyone else. $\endgroup$
    – geometrian
    Dec 9, 2014 at 21:37

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You're confusing mass with weight. Say, somewhere in space, there's a ball, and nearby there's no other sun/planet/anything. Then that ball will experience no force and thus would appear to have no weight. but it will still have mass. Weight is a force that a mass experiences due to gravity. mass is due to atoms and molecules. If something pulls (gravitational pull) those atoms/molecules, then they will experience a force and thus they will appear to have some weight if you decide to measure that weight. If there is no gravity felt by an object, which losely put, means that there is no force from any neighboring massive body. Remember, weight = mass x gravity. where weight is the force and gravity is the acceleration, or $F=ma$. Thus, mass is an inherent property of matter. If there is matter, it may have mass (if it's travelling at speeds << c), and it may have some weight, provided it is attracted by another object.

I gave somewhat a very simplistic explanation of how mass/matter is defined. I could go into proper details but the fact is that the term matter has no universally-agreed definition. You can find more detailed explanation here: http://en.wikipedia.org/wiki/Mass. But you need to know some physics beforehand to properly understand.

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  • $\begingroup$ @Jim My understanding was that "relativistic mass" was considered by many to be an incorrect and unuseful concept. en.wikipedia.org/wiki/Mass_in_special_relativity#Controversy $\endgroup$
    – Sean
    Sep 25, 2015 at 17:29
  • $\begingroup$ @Sean You're right. I posted that comment 9 months ago and I don't know what I must have been smoking. $\endgroup$
    – Jim
    Oct 1, 2015 at 13:14
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Even without gravity, momentum conservation will still hold.

If you elastically scatter an unknown mass $m$ with an initial (known) velocity $v$ against a known mass at rest, for instance we can take the SI standard of $1$ Kg, then from the resulting measured velocities you should be able to find $m$.

Thus Yes, there will still be a mass.

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Yes, there will still be a mass because mass is the amount of matter in an object so there will always be matter in an object.

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  • $\begingroup$ There is no need to answer such questions where there is a lack of research and has garnered so many downvotes. Moreover your answer is more of a comment than an answer. Please check other comments which seem very much logical in comparison to yours. $\endgroup$
    – SchrodingersCat
    Sep 25, 2015 at 16:42
  • $\begingroup$ @Aniket No need to get at a new user like that either. It's a low level answer, but he's not wrong. $\endgroup$
    – Sean
    Sep 25, 2015 at 16:57
  • $\begingroup$ @Sean Don't get me wrong. I wanted to point out the difference between a comment and an answer. And I think it is better to tell a new user how and what to answer in the very beginning itself. $\endgroup$
    – SchrodingersCat
    Sep 25, 2015 at 17:01
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like the quantum mechanics if you could not measure something so that not exists/ how could you detect a mass if there is no force even if you get close to that to touch it you have a mass yourself so the force would appear and if not you are contradicting newtons law of gravity
so the argument is not that simple mass and force are defined by each other

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    $\begingroup$ This answer is not particularly clear what you're trying to say. $\endgroup$
    – Kyle Kanos
    Nov 24, 2015 at 19:45
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If there was NO gravity, (anywhere), there would be nothing else either; what would hold anything together ?? Gravity and the Coulomb force are the only two infinite range forces in nature. The Coulomb force pushes (between like objects) and gravity only pulls. Earnshaw's theorem says there is NO stable (static) system of electric charges.

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  • $\begingroup$ Sloppy reasoning; you can have structures (e.g. Hydrogenic systems) without gravity. Is not "only gravity" that pulls with infinite range, but also electromagnetism. $\endgroup$
    – Alex A
    Jun 26, 2014 at 16:39
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    $\begingroup$ What holds you together? I guarantee you that gravity is not responsible for keeping your head on your shoulders $\endgroup$
    – Jim
    Jan 8, 2015 at 19:44
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Mass is an inherent property of Matter Black holes exhibit Gravity, so the matter consumed is still a form of Matter. If matter accelerated to the speed of light, theory states it will transform into pure energy, which seems to indicate that the matter being sucked into the black hole does not reach that speed, as pure energy has no mass, and hence would not exhibit gravity. Theory all the matter inside the black hole is compressed to 1 Planck length, and this tiny compressed form of matter is the 'Singularity', the size of the Singularity being exactly the same if it has the matter of 40 billion suns in it, or just the matter of a single star, only difference being the distance from the singularity to the event horizon, this would indicate the event horizon is a property of the singularity, yet some theorise you can have naked 'Singularity', and some force can stretch this naked singularity into a connected string again only 1 Planck length wide, however I have not seen anyone clearly theorize how you could get a naked singularity or associated cosmic string.

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