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The entire universe is made up of stuff—or, as scientists call it, matter. Matter is what makes up everything around us. Anything that has mass, meaning it takes up space, and has stuff inside is matter. Whether a solid, liquid, or gas, if you can contain it, it’s matter. But why does matter matter, and why do we spend a solid (pun intended) amount of time in science class learning about it?
The answer is that we live in a physical world. If we can hold it, feel it, and smell it, it’s because it’s made of physical particles. Because of this, matter has physical properties that we can observe and measure. And in order to make sense of and draw conclusions about that world, we need to be able to define the physical properties around us.
Being able to define these physical properties is helpful to those who wish to answer questions about particular matter, such as: How much space does it take up? What color is it? What is it? Matter can be defined by its physical properties and by the way it physically changes. Some physical changes are the result of a change in energy, but these changes don’t change the chemical makeup of the matter. Using these changes in the physical properties of matter—and the points at which these changes occur—are a good way to define matter.
In the rest of this article, we’ll review one particular physical measurement of matter: density. Why? Because density is cool! The density of an object isn’t something you can easily estimate based on looking at an object, and knowing an object’s density is important to understanding its relationship to other objects it may interact with.
Basically, an object’s density depends on how closely the tiny particles that make up matter are packed together. Objects with a high density have particles that are more tightly packed than objects with a low density. For example, think about the difference between a golf ball and a ping-pong ball. Even though they are about the same size, golf balls are heavier because they have a higher density.
Knowing an object’s density is useful in many ways. One of the more practical applications of knowing an object’s density is in using it to calculate mass, which is useful in engineering, among other areas. Take this example from sciencing.com:
Using the simple formula m = ρ × V, where m = mass, ρ = density, and V = volume, if you know how much space there is in a van and what the maximum safe load the van can carry is, you can work out whether filling it with a specific material will be safe. You could also use the original version of the equation to work out what the densest material you could safely transport is.
The degree to which an object floats or sinks, or its buoyancy, is also related to its density. Generally, if something is denser than water, it will sink, but if something has a lower density than water, it will float. More specifically, an object will start to float when the weight of the water it displaces (due to the surface area making contact with the water and how far it pushes the water down) matches the weight of the object, but if the object is denser than water, the weight of the water it displaces can never match the weight of the object, so it will continue to sink.
Now that you know the basics of one of matter’s most interesting physical properties, you can use the following simple sets of metal masses from hBARSCI to investigate density easily on your own! The following kits, part of the Eisco Labs Density Investigation series, are designed to help students identify and figure out mass and understand the relationship between mass/volume/density, specific heat and specific gravity, and other introductory physics and chemistry concepts.
This density cube set includes six metals: brass, lead, copper, iron, aluminum, and zinc. They have a wide range of educational applications for all grade levels, including density investigation, specific heat, and specific gravity exploration. When students are not told beforehand which cubes are which metal, they can use calculations and buoyancy to identify the metal based on known values.
Or, try your hand at calculating the density of cylinders. In this five-piece equal mass cylinder set, which includes aluminum, brass, nylon, acrylic and polyvinyl chloride, the five cylinders in each have an equal mass, measuring 0.5" (12.5mm) in diameter but varying in length from 0.5" to 4". The set includes a complete instruction manual that gives a background on density, specific gravity, and specific heat and includes inquiry-based student activities with capture sheets.
Finally, Eisco Labs offers a 12-piece density metals set. This comprehensive set includes an assortment of shapes and sizes of two samples of the following metals: brass, iron, aluminum, copper, zinc, and lead. Masses range from 12–25g, giving learners a wide range of different values to study.
Each of these sets is useful in teaching all aspects of the physical properties of matter and offer students a specific investigation into density.