MadSci Network: Physics

Re: could there be different forces of gravity from materials with same mass

Date: Sat Aug 19 05:19:43 2006
Posted By: Dan Bolton, Undergraduate, Astronomy and Physics, Last: University of Hawaii at Hilo
Area of science: Physics
ID: 1155707664.Ph



I have met several scientists that are skeptical of the the Dark Matter theory; however, I am a believer to be sure.  Gravity is a very strange force, and scientists are working hard even today to test new theories about it.  But even as we endeavor to learn the mysteries of gravity, there seems to be a constant gravitational force produced from all objects, and the amount of gravity is related directly to the amount of mass.


It should be understood that mass is a unit of measurement that describes an amount of a substance, be it matter, energy, or both; and not a substance itself.  You can’t have a glass full of mass. So even if there were two different materials of the same mass, the masses are the same.  A kilogram of feathers would fill a fairly large box, but a kilogram of lead (Pb) can be in the shape of a very small brick; both have the same mass (one kilogram) and therefore the same amount of gravity.   Again, it is the mass that determines the amount of gravity, not material.  The periodic table lists all of the known types of visible matter by their elemental basics.  Each element has a different and identifiable mass.  All objects – that we know of – are made from elements on this list; including all of the stars in all of the galaxies.  It is no coincidence that all the natural elements on the periodic table come from stars (see nucleosynthesis).  The gravitational force (gravity) is the amount of attraction, measured in units of force, between two objects with mass.  So if I understand your question correctly, the answer is no.  Different materials with the same mass cannot have different forces of gravity. 


Now, if you are wondering if it is “possible” that there exists an alternative macroscopic attracting, or repelling, force within matter… There doesn’t seem to be any other fundamental forces and the universe seems to make sense with the four that we have; the electromagnetic, strong, weak, and gravitational force.  I dare to say impossible; however, no one really knows what dark matter is.  It may just be impossible to prove.


Our measurements of gravity have been challenged for about as many years as we have known about gravity.  If our measurements and physics are right, and physics is isotropic across the universe, then we can prove that “something” is there pulling and accelerating galaxies.  Until we know more, we just call it Dark Matter.  It is dark to all wavelengths of light and it reacts gravitationally with visible matter.  All matter should produce gravity related directly to its mass.


Hope that helps!



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