PASCO SE-9076 Constant Velocity Tubes - Manual (Page 8)

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Constant Velocity Tubes 012–06697B
Pre-Lab Exercise: Graphing in the Lab
Purpose
To help students develop graphing skills that will be needed to complete the activities
with the Constant Velocity Tubes
Background
Graphs are an effective way of presenting numerical data in a laboratory report, but that
is not their only use. Graphs can also be used to determine the mathematical relationship
between two variables. In the following graphing exercise, you will work with two
types of variables: an independent variable and a dependent variable. An independent
variable is the part of the experiment that you change in a measured, controlled way.
The dependent variable is the part of the experiment that changes as a result of the
changes in the independent variable.
This exercise will help you develop the graphing skills you will need in your experiments
with the Constant Velocity Tubes. You will draw a graph of experimental data that were
previously collected.
In a previously conducted experiment, a measured volume of liquid mercury
(independent variable) was added to a glass beaker, and then the mass of the beaker and
mercury (dependent variable) was determined with a platform balance.
Procedure
1. In an experiment, there are generally several variables that might possibly affect
the dependent variable. If we can arrange to allow only one of these to vary and
hold the others constant during the experiment, it is far easier to interpret the results.
Besides the volume of liquid, the kind of liquid is an example of a variable which
might possibly affect the mass reading; thus the kind of liquid used should not be
changed during the experiment. Can you think of any other variables that should
be held constant in this experiment?
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2. For the first data point of this experiment, the beaker was filled to the 250 ml mark
with liquid mercury, and the mass reading from the pan balance was 3,600 g. Next,
the beaker was emptied and then filled to the 50 ml mark. The mass reading was
then 1000 g. Notice that these first two sets of data represent two extreme
possibilities. Why do you suppose such values were chosen?
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