Question 13 - Reading and Writing Practice Test for the PSAT/NMSQT Exam

Before we go on to discuss Newton’s other work, we want to take a brief look at some terms that will be important to sort out clearly. We begin with mass, which is a measure of the amount of material within an object.

The volume of an object is the measure of the physical space it occupies. Volume is measured in cubic units, such as cubic centimeters or liters. The volume is the “size” of an object. A penny and an inflated balloon may both have the same mass, but they have very different volumes. The reason is that they also have very different densities, which is a measure of how much mass there is per unit volume. Specifically, density is the mass divided by the volume. Note that in everyday language we often use “heavy” and “light” as indications of density (rather than weight) as, for instance, when we say that iron is heavy or that whipped cream is light.

The units of density that will be used in this book are grams per cubic centimeter (\(\text{g}/\text{cm}^3\)). If a block of some material has a mass of \(300\) grams and a volume of \(100\, \text{cm}^3\), its density is \(3 \text{g/cm}^3\). Familiar materials span a considerable range in density, from artificial materials such as plastic insulating foam (less than \(0.1 \,\text{g/cm}^3\)) to gold (\(19.3 \,\text{g/cm}^3\)). Table \(3.1\) gives the densities of some familiar materials. In the astronomical universe, much more remarkable densities can be found, all the way from a comet’s tail (\(10^{-16}\, \text{g/cm}^3\)) to a collapsed “star corpse” called a neutron star (\(10^{15} \,\text{g/cm}^3\)).