Data in tables can be extremely useful and informative.
Sometimes, though, making a graph of data makes
relationships between variables much more clear than a
table can. In this activity you will graph two sets of data
on the same sheet of graph paper. You will explore what the
graph can tell you about the data. You will be introduced
to the idea that direct proportions between variables can
be evaluated using a graph.
Here are the data you will graph:
Volume (± 0.1 mL)
Mass (± 0.1 g)
Volume (± 0.1 mL)
Mass (± 0.1 g)
To make your graphs:
Make an easy-to-read graph that fills the space you
make available for it (no blank spaces). Volume goes on
the x-axis and Mass goes on the y-axis.
This is best accomplished by setting up your axes
before you start graphing.
Make sure the largest value to be graphed on each
axis will be on the graph.
Select a spacing on the available scale so that
you can easily figure out where each decimal is
Use a ruler to draw a line of best fit: this line may
not go through the data points! It just needs to pass
as closely as possible to all the data points.
Using points on the line (not data
points!) determine the slope of the line; the
slope is the constant of proportionality and shows how
mass relates to volume. The slope is calculated as the
change in mass over the change in volume. Density is
defined as D = m/V.
Using your graph or your knowledge of algebra find
the y-intercept of the line
Determine the correct units for both the slope and
Write the equation of the line in y-intercept form
using variables appropriate to the data. That is,
m for mass instead of y and
V for volume instead of x.
Direct proportions have graphs which show a straight line as the best way to connect the dots. For two variables in a direct proportion, when one gets larger, the other does, too. Inverse proportions have graphs which show an inverse curve as the best way to describe the pattern of dots. For two variables in an inverse proportion, when one variable increases, the other decreases.
Answer these questions on a separate sheet of paper using
complete sentences. Show work for all mathematical
If you compare two pieces of the same material that
have different volumes, which one has a larger mass: the
smaller one or the larger one? Is there a direct or an
inverse proportion between the mass of a sample and the
Give the equation of the line for the copper data.
Also, give the equation of the line for the aluminum
What units should be used when you report the slope?
Why? Consider that slope is defined as the change in
y divided by the change in x
Δy = y2 –
y1 and Δx =
x2 – x1
What does the value of the slope of your graph
Is the slope the same for each point on the graph?
Is the density of copper the same for every sample?
How about the aluminum? Justify your answer based on the
graph you made.
Using your graph, find the volume of 155 g of
Using the equation of the line, calculate
the volume of 155 g of Al.
Show your work.
Why is the slope of the line for the copper data
different from the slope of the line for the aluminum
The y-intercept is the value of the variable on the
y-axis when the value on the x-axis equals zero. With
ideal data in an ideal world, what should the
value of the y-intercept be for both graphs? Why?
For this assignment you must turn in the answers to these
questions and your sheet of graph paper showing both
graphs and including all of the information required in
the instructions for making the graphs. This will count
toward your lab grade.