Morgan Extra Pages
Graphing with Excel (revised 6/10/13)
to be carried out in a computer lab, 3rd floor Calloway Hall or elsewhere
Name Box
Figure 1. Parts of an Excel spreadsheet.
The Excel spreadsheet consists of vertical columns and horizontal rows; a column and row intersect
at a cell. A cell can contain data for use in calculations of all sorts. The Name Box shows the currently selected cell (Fig. 1).
In the Excel 2007 and 2010 versions the drop-down menus familiar in most software screens have
been replaced by tabs with horizontally-arranged command buttons of various categories (Fig. 2)
Figure 2. Tabs.
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Open Excel, click on the Microsoft circle, upper left, and Save As your surname.xlsx on the desktop. Before leaving
the lab e-mail the file to yourself and/or save
to a flash drive. Also e-mail it to your instructor.
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EXERCISE 1: BASIC OPERATIONS
Click Save often as you work.
1. Type the heading “Edge Length” in Cell
A1 and double click the crack between
the A and B column heading for automatic widening of column A. Similarly,
write headings for columns B and C and
enter numbers in Cells A2 and A3 as in
Fig. 3. Highlight Cells A2 and A3 by
dragging the cursor (chunky plus-shape)
over the two of them and letting go.
2. Note that there are three types of cursor
crosses: chunky for selecting, barbed for
moving entries or blocks of entries from
cell to cell, and tiny (appearing only at
the little square in the lower-right corner
of a cell). Obtain a tiny arrow for Cell
A3 and perform a plus-drag down Column A until the cells are filled up to 40
(in Cell A8). Note that the two highlighted cells set both the starting value of
the fill and the intervals.
Figure 4. A formula.
5. Highlight Cells B2 and C2; plus-drag
down to Row 8 (Fig. 5). Do the numbers look correct?
Click on some cells in the newly filled
area and notice how Excel steps the row
designations as it moves down the column (it can do it for vertical plus-drags
along rows also). This is the major programming development that has led to
the popularity of spreadsheets.
Figure 3. Entries.
3. Click on Cell B2 and enter a formula for
face area of a cube as follows: type =,
click on Cell A2, type ^2, and press Enter (note the formula bar in Fig. 4).
4. Enter the formula for cube volume in
Cell C2 (same procedure, but “=, click
on A2, ^3, Enter”).
Figure 5. Plus-dragging formulas.
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Figure 6. Creating a scatter graph.
6. Now let’s graph the Face Area versus
Edge Length: select Cells A1 through
B8, choose the Insert tab, and click the
Scatter drop-down menu and select
“Scatter with only Markers” (Fig. 6).
7. Move the graph (Excel calls it a “chart”)
that appears up alongside your number
table and dress it up as follows:
a. Note that some Chart Layouts have
appeared above. Click Layout 1 and
alter each title to read Face Area for
the vertical axis, Edge Length for the
horizontal and Face Area vs. Edge
Length for the Graph Title.
b. Activate the Excel Least squares
routine, called “fitting a trendline” in
the program: right click any of the
data markers and click Add Trendline. Choose Power and also check
“Display equation on chart” and
“Display R-squared value on chart.”
Fig. 7 shows what the graph will
look like at this point.
c. The titles are explicit, so the legend
is unnecessary. Click on it and press
the delete button to remove it.
Figure 7. A graph with a fitted curve.
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8. Now let’s overlay the Volume vs. Edge Length curve onto the same graph (optional for
203L/205L): Make a copy of your graph by clicking on the outer white area, clicking ctrl-c
(or right click, copy), and pasting the copy somewhere else (ctrl-v). If you wish, delete the
trendline as in Fig. 8.
a. Right click on the outer white space, choose Select Data and click the Add button.
b. You can type in the cell ranges by hand in the dialog box that comes up, but it is easier to
click the red, white, and blue button on the right of each space and highlight what you
want to go in. Click the red, white, and blue of the bar that has appeared, and you will
bounce back to the Add dialog box. Use the Edge Length column for the x’s and Volume
for the y’s.
c. Right-click on any volume data point and choose Format Data Series. Clicking Secondary Axis will place its scale on the right of the graph as in Fig. 8.
d. Dress up your graph with two axis titles (Layout-Labels-Axis Titles), etc.
Figure 8. Adding a second curve and
y-axis to the graph
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EXERCISE 2: INTERPRETING A LINEAR GRAPH
Introduction: Many experiments are repeated a number of times with one of the
parameters involved varied from run to run.
Often the goal is to measure the rate of
change of a dependent variable, rather than a
particular value. If the dependent variable
can be expressed as a linear function of the
independent parameter, then the slope and yintercept of an appropriate graph will give
the rate of change and a particular value,
respectively.
An example of such an experiment in
PHYS.203L/205L is the first part of Lab 20,
in which weights are added to the bottom of
a suspended spring (Figure 9).
ing weights in newtons of 0.49, 0.98, etc.
The weight pan was used as the pointer for
reading y and had a mass of 50 g, so yo could
not be directly measured. For convenient
graphing Equation 1 can be rewritten:
-(Mg) = - ky + kyo
Or
(Mg) = ky - kyo
(Eq. 1′)
Procedure
1. On your spreadsheet note the tabs at the
bottom left and double-click Sheet1.
Type in “Basics,” and then click the
Sheet2 tab to bring up a fresh worksheet.
Change the sheet name to “Linear Fit”
and fill in data as in this table.
Hooke’s Law
Experiment
y (m)
-Fs = Mg (N)
0.337
0.49
0.388
0.98
0.446
1.47
0.498
1.96
0.550
2.45
2. Highlight the cells with the numbers,
and graph (Mg) versus y as in Steps 6
and 7 of the Basics section. Your Trendline this time will be Linear of course.
Figure 9. A spring with a weight
stretching it
This experiment shows that a spring exerts a
force Fs proportional to the distance
stretched y = (y-yo), a relationship known
as Hooke’s Law:
Fs = - k(y – yo)
(Eq. 1)
where k is called the Hooke’s Law constant.
The minus sign shows that the spring opposes any push or pull on it. In Lab 20 Fs is
equal to (- Mg) and y is given by the reading
on a meter stick. Masses were added to the
bottom of the spring in 50-g increments giv-
If you are having trouble remembering
what’s versus what, "y" looks like "v",
so what comes before the "v" of "versus"
goes on the y (vertical) axis. Yes, this
graph is confusing: the horizontal (“x”)
axis is distance y, and the “y” axis is
something else.
3. Click on the Equation/R2 box on the
graph and highlight just the slope, that
is, only the number that comes before the
“x.” Copy it (control-c is a fast way to
do it) and paste it (control-v) into an
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empty cell. Do likewise for the intercept
(including the minus sign).
SAVE
YOUR FILE!
5. The next steps use the standard procedure for obtaining information from linear data. Write the general equation for
a straight line immediately below a
hand-written copy of Equation 1′ then
circle matching items:
(Mg) = k y + (- k yo)
y
= mx+ b
(Eq. 1′)
6. Solve Equation 2 for k, that is, rewrite
left to right. Then substitute the value
for slope m from your graph, and you
have an experimental value for the
Hooke’s Law constant k. Next solve
Equation 3 for yo, substitute the value for
intercept b from your graph and the
value of k that you just found, and calculate yo.
7. Examine your linear graph for clues to
finding the units of the slope and the yintercept. Use these units to find the
units of k and yo.
Note the parentheses around the intercept term of Equation 1′ to emphasize
that the minus sign is part of it.
8. Present your values of k and yo with their
units neatly at the bottom of your
spreadsheet.
Equating above and below, you can create two useful new equations:
9. R2 in Excel, like r in our lab manual and
Corr. in the LoggerPro software, is a
measure of how well the calculated line
matches the data points. 1.00 would indicate a perfect match. State how good a
match you think was made in this case?
slope m = k
(Eq. 2)
y-intercept b = -kyo
(Eq. 3)
10. Do the Homework, Further Exercises on
Interpreting Linear Graphs.
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