Taking into account the definition of density, assuming all other conditions remain the same, increasing mass will cause an object's density to increase.
Density is defined as the property that matter, whether solid, liquid or gas, has to compress into a given space. That is, density is a quantity referred to the amount of mass contained in a given volume.
Density is an intensive property since it does not vary with the amount of substance.
Since density is the relationship between the mass and the volume of a substance, its calculation is defined as the quotient between the mass of a body and the volume it occupies:
In the previous expression it can be observed that the density is inversely proportional to the volume: the smaller the volume occupied by a certain mass, the greater the density.
On the other hand, density is directly proportional to mass: the greater the mass, the greater the density.
Finally, assuming all other conditions remain the same, increasing mass will cause an object's density to increase.
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