Volume, Mass, and Density for Dummies

Density of solids vs. fluids

As our researchers wander the internet in search of knowledge-deficient posts by freelancers, they often run across what seem to be well- researched and -written material that, on closer inspection, makes precious little sense. Take, for instance, David Chandler and his Sciencing.com (a niche site Leaf Group is populating with old eHow.com material) article titled "Volume vs. Mass Density." It looks right at first, but...

Chandler, who claims to have been "educated in international studies and microbiology," starts off on a weak note given the ambiguity of the "title." In all seriousness, the phrase "volume vs. mass density" makes no sense in a context-free setting. Chandler's attempts to create context are where he gets into trouble. He begins, as one might expect, by defining density:

"Volume is one of the parameters for density, the other being mass. Volume measures how much space a substance occupies. Mass measures the amount of matter in the substance. Density then shows the amount of matter in a given space for a substance..."

...which seems a rather clumsy definition, especially given that density is an inherent physical property of a substance. Clumsy, however, seems to be a watchword at eHow... errr, Sciencing. Chandler goes on to intone that

"Density is often presented as grams per cubic centimeter (g/cm3)." We liked that "often" bit. It's not what someone with a background in science would say, though: a scientist might say that the SI units of density are g/cm³ (we're not sure of the notation in the original eHow article, but are aware that the migration to Leaf Group niches has messed up some html symbols). David goes on to explain how to increase density, though his explanation is quite sophomoric: "If the volume for a mass of substance is decreased, the density increases. For example, compressing a gas into a gas cylinder increases the density of the gas." Have fun changing the density of a solid or a liquid that way, Dave! Ditto with his ideas for decreasing the density of a substance:

"Increasing the volume of a mass of substance decreases the density. Releasing a gas from a compressed gas cylinder will decrease the density of the gas that was contained."

Chandler completes his little ditty by blathering briefly about "compressibility," during which he declaims that "Liquids and solids resist changes to their volume and are considered incompressible." Dave also has a little to say about density contrasts, though he seems have the impression that only liquids are affected.

Chandler has nothing to say about the effects of temperature on density, nor does he bother to mention that the density of an unknown can be used (along with other physical properties) to determine its composition. In other words, Dave did little more than reword a few paragraphs from his references, leaving out the important concept "The density of a material helps to distinguish it from other materials" in the first paragraph of one of his references. Yup, that's Dumbass of the Day work...

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