Chemistry Reference
In-Depth Information
Lesson 2- 6: Density Calculations
Try asking a friend why a balloon floats, and it is likely that he or she
will incorrectly say, “Because it is light.” Then ask the friend why a hot-air
balloon with several people aboard floats, and he or she may not know
what to say. Understanding density will help you understand many things
that you can observe in the real world.
Density is defined as the amount of matter in a given unit of volume. A
material with high density will have its particles (atoms or molecules) tightly
packed together. A material with low density will have more space between
its particles. There is more to density than just size. Just as you can have a
large object with high density, you can have a large object with low density.
The relationship between the density, volume, and mass of an object can
be best understood by looking at the formula for density.
The Formula for Density
mass
volume
m
v
Density =
or
D =
We can see from the formula that the density of the object is directly
proportional to the mass of the object. This means that if you could double
the mass of an object without changing its volume, its density would also
double. The formula also shows us that the density of an object is inversely
proportional to its volume. This means that if you were to double the volume
of an object, without changing its mass, its density would be divided by 2.
Whether or not something floats depends upon its density, compared
to the density of the material that it is floating in. A balloon will float in the
air if it is less dense than the air around it. Icebergs float in liquid water
because they are less dense than the water.
Did you know that you can control your density to a certain extent?
Have you ever tried to float on the surface of a pool, or any body of water?
How did you do it? Did you fill your lungs up with air, before lying across
the surface of the water? If so, you decreased your density!
When you fill your lungs with air, your chest expands, which increases
your volume. It is true that you also increase your mass by some insignifi-
cant amount as you draw in molecules from the air around you, but your
volume will increase by a much more significant amount. Look at the for-
mula for density, and think about what happens to your density as your
chest expands, and your volume increases.
