Graphing Experimental Data
Objective:
In this exercise you will review how to collect and graph experimental data.
Background:
A graph represents the relationship between a pair of variables.
Normally, a wellplanned experiment
results in the measurement of one physical or chemical property and its dependence on another.
The
property which is changed in a controlled manner is called the "independent variable", while the variable
which responds to this change is called the "dependent variable".
As a matter of form, the independent
variable is plotted on the horizontal, or xaxis, while the dependent variable is plotted on the vertical, or y
axis.
The xaxis is referred to in mathematics as the
abscissa
, while the yaxis is referred to as the
ordinate
.
The graph should expand to fill as much of the graph paper as possible so that the experimental data can be
plotted with the greatest precision.
Once the data points have been plotted, the line best
represented by the points is drawn.
Due to
experimental uncertainty and error, the data points will not lie exactly on this line.
The drawing of a line is
equivalent to taking a weighted average of the data points.
The best line should be drawn with a
transparent straight edge or ruler so that all of the points can be seen at the same time (see Figure 1).
y
=
m
x
+
b
Δ
x
Δ
Δ
y
Slope = m =
Δ
y
Δ
x
Title
Abscissa (independent variable)
O
r
d
i
n
a
t
e
(
p
v
l
)
Figure 1
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View Full DocumentOnce the graph has been made, it is often useful to determine an equation in order to represent the
information in the most concise way possible.
The discussion herein deals only with straightline
relationships.
In addition to expressing the relationship between variables, the slope and yintercept of a
straight line can often be related to physical values.
The general form for the equation of a straight line relating the variables x and y is
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 Spring '10
 none
 Thermodynamics, pH, data points, Erlenmeyer flask

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