Because it produces gravimotion that is gravitational motion-volumes in its surrounding, the very mass of matter or the very mass of subatomic particles is occurring as motion-volumes in gravimotion's interpretation of Nature.
The (so-called) mass of any subatomic particle is occurring as concurring motion-volumes toward a common point center of gravity, at the image of the gravimotion surrounding it.
Because the motion-volumes implementing the present mo(ve)ment (blue in the illustration) are absolute-motion-volumes, when two of them happen to butt heads on (black in the illustration) they cannot penetrate each other front end, they stall and end into entangled pairs; such entangling mandates that absolute-motion-volumes have front tips able to penetrate other absolute-motion-volumes by the side but are rebounding or stalling when the collisions are occurring on their front tips.
Occurring as 2 absolute-motion-volumes in opposition, any such pair is now storing a high supply of constrained motion (energy in science), susceptible in reverse to be blasted away.
Several of these explosive pairs may congregate together (only 3 pairs are shown in the illustration), all aggregated around a common center of gravity; such high density delineates the (so-called) mass of a subatomic particle.
This high density of concurring absolute-motion-volumes (mass in science), contrary to its surrounding gravimotion, is occupying most of its allocated present mo(ve)ment volume, and can no longer be easily penetrated by other material particles of similar constitution.
Note that, in quantum mechanics, particles pop haphazardly out of empty space and are made of energy; in gravimotion, space-time is occurring as absolute-motion-volumes out of which pop out particles occurring as pairs of absolute-motion-volumes.
In return, the demolition of such particle amounts at reversing it's explosive gravimotion into a blast of motion precisely described mathematically by Einstein's famous E=mC2 equation.
" m " in this equation becomes a number with no unit, only defining the quantity of C2 pairs involved, like " m = one hundred C2" or " m = one million C2"; these light's speed squared " C2 " are actually implementing matter; and a great number "m" of "C2" does not implement a "quantity" moving faster than "C" as the "m"s are occurring in pairs of absolute-motion-volumes butting each other in opposite direction, maintaining them in an inert state motion wise.
The squared C2 of light speed reflects (in this mind of mine) the entwining of the 2 absolute-motion-volumes embodying the pairs.
One could imagine a subatomic particle constituted of trios rather than pairs; the three motion-volumes, of each trio, butting at each other and oriented at 240 degrees from each other. And that suggests that Einstein equation could also be written as E=mC3.
On how the present mo(ve)ment (space-time) produces material particles
The upper illustration shows how several absolute-motion-volumes pairs, within the present mo(ve)ment, got aggregated together, yet without being transformed to a material particle, which amounts to an unfinished business necessitating to better describe the process.
The lower illustration shows the head-on collision of only two absolute-motion-volumes within the present mo(ve)ment, and the subsequent forming of a subatomic particle.
In this case, the material particle, which popped out of the present mo(ve)ment (space-time in science) is characterized by only 2 hemispherical spinning motions; the present mo(ve)ment's two absolute-motion-volumes before colliding appear in blue, indicating they are invisible to human eyes; on the other hand, the material subatomic particle emerging out of the collision, whether opaque or translucid because material is represented in black color.
Gravimotion interpretation of motion relativity
An out of equilibrium implemented within each pair of a material body absolute-motion-volumes engenders an out of equilibrium in each pair of that body's surrounding gravimotion, setting the body into motion; a loss of equilibrium within each of these pairs, is in effect implementing an over-all motion of that body lower than "C" that is lower than the speed of light, and given the name relative-motion-volume.