CHM 109 Excel Refresher Exercise adapted from Dr. C. Bender s exercise

Transcription

1 CHM 109 Excel Refresher Exercise adapted from Dr. C. Bender s exercise (1 point) (Also see appendix II: Summary for making spreadsheets and graphs with Excel.) You will use spreadsheets to analyze data for three of the laboratory exercises this semester. This exercise assumes you have some familiarity with Excel, which is the spreadsheet program that you will find on computers on the USC Upstate campus. If you prefer to use another program for your work, that is fine, but you must be able to make use of the program on your own, and the final product must be the same. If you have not used a spreadsheet program recently, ask for help as often as necessary. Objectives After completing this exercise students should be able to: 1. Enter data, and cut, copy, and paste from one cell to another. 2. Perform simple mathematical calculations on cells. 3. Prepare graphs with appropriate labels, space use, and axis dimensions. 4. Use the trendline function to perform a linear regression on a data set. 5. Interpret the slope and R 2 value of the trendline analysis to find a rate and assess the goodness of fit of a data set to a straight line. Procedure Shown as a screen capture on the next page are two data sets of distance and time measurements based on imaginary bike rides that you took with a friend. The first entry in the location column indicates where you started your trip. The last entry indicates where your trip ended. Assume that you are such a serious cycler that you did not get off of your bike until the end of the trip. In other words, you pedaled continuously! (Note: Distances and times shown are running totals. That is, it was 51.9 km from the start of the first ride in Greer to Cowpens, and it took you 1.80 hours to pedal that distance.) There is also a set of data based on heart rate measurements taken at three points during the second trip. Making a Table 1. Open Excel, and put your name in cell A1. Enter the first title Ride from Greer, SC to Gastonia, NC in cell A2. Skip a line and start the first table in cell A4, then save the spreadsheet. Make your tables look just like the screen capture on the next page (same location showing table borders). Don t add color to the background of the rows as it would require additional ink when printing. Save frequently during the exercise and save a copy to a separate location. Students often do this by saving to a USB drive, or by saving to the desktop and then ing a copy of the file to themselves. Even if you feel you have completed the exercise before leaving today, save it, because you may find changes that you want to make later on. Ask your instructor any time you have difficulty during today s exercise. 2. Check that you have your cells properly aligned by clicking on the cell that says Blue Ridge Parkway. It should be cell E9. You can check the cell designation by looking at the gold highlighted column (E) and row (9), or by looking at the cell indicator in the area just above the A column. (See below.) If this cell does not have the E9 indicator, select, right-click, and cut and paste all of the data to align them properly. Make sure the number in C8 is 1.80, not 1.8. The easiest way to make this adjustment is with one of the buttons in the number section in the tool bar. Center the data in each column by highlighting the data and using the appropriate button in the alignment section of the tool.

2 3. Now you will do a few simple calculations. Let s find out how far it is from Lyman to Gaffney. To do this, you need to subtract the distance of these two locations. a) Always begin an equation in Excel with an equal sign, =, and use cell designations instead of numbers when possible. This means you would type =B9-B6 in cell B23 (not = ). The cell should show a numerical answer, but when you look in the active bar (the white bar next to the f x), it will show the equation you entered. b) Next, how long did it take to ride from Lyman to Gaffney? You could determine this by entering =C9-C6 in cell C23, but instead try the following: select cell B23, place the cursor on the lower right corner of the cell (the cursor show look like an addition sign) and drag to cell C23. What happened? You can see from this that the spreadsheet has some reasoning functions built in. c) Recalling that speed is distance divided by time, calculate your average speed over this part of the trip by typing =B23/C23 into cell D23. If you have the D column set to default width, the result should be km/hr (don t show units for spread sheet calculations). Let s see if changing the column width changes the way the result is displayed. To change the column width, take the cursor and place in on the bar between the D and E label blocks at the top of the spreadsheet. When the cursor is in the appropriate location to change cell width, it will change it appearance from the white cross to a short vertical black bar crossing a horizontal bidirectional arrow. Click and drag to the right to increase the width of the D column. You will see that the number of places displayed has increased. d) How many places should be displayed for this calculation? When you have studied the significant figure and rounding concepts, you know that there should be three significant figures in this answer. To set the number of places displayed, right-click on cell D23, and when the menu box opens, click Format Cells, go to the Number tab, and select Number from the Category list, 1 from the Decimal places list, and then click OK. The 1" here means that one place after the decimal point will be displayed. You can also vary the number of decimal places shown by clicking one of the two boxes in the numbers section of the tool bar (Each button has a small blue arrow). Cell D23 should now display 33.6.

3 Now go back up to the top of the spreadsheet and adjust the width of all columns in the table so that they are just wide enough for all of the numbers/text in each column to be read. Don t adjust for width of the titles, because they will overlap the empty adjoining cells. Please make this adjustment for all of your lab work this semester!!! e) Do a similar set of calculation for the Spindale to Marion section of your second trip. Place them in cells F23, G23 and H23. Make sure all three numbers have three places (significant figures.) f) Another useful calculation is to determine the average of a set of numbers. There is a built-in function in Excel to determine this. Use this function to calculate the average heart rate for the second trip based on the three measurements provided. In cell H19, type =AVERAGE(F18:F20). The cell designations inside the parenthesis can be typed in or introduced by highlighting F18 thru F20. When determining an average, it is common to also determine a deviation, or how much the numbers being averaged vary from the average. For this exercise, calculate the standard deviation by typing the following in cell H20, =STDEV(F18:F20). Now round both the average and standard deviation to the ones place. This should give you three digits for the average and two digits for the standard deviation. g) There is one more item to add to your spreadsheet. In cells A27 and A28, type I understand that turning in someone else's spreadsheet as though it is my work is a violation of the student honor code. The first half of the sentence should start in A27 (it will run over the top of other cells). Type the second half in A28. Next click File, then Print and preview the picture of your file to make sure everything fits on one page. If it doesn t, click on Portrait Orientation in the Settings column on the left and choose Landscape Orientation. You might also need to click on Scaling near the bottom of the Settings column and choose Fit Sheet to One Page. Your instructors will also want to see the column headings on the spreadsheet, so click on Page Setup in small blue letters at the bottom of Settings column on the left and choose the Sheet tab and under Print, check Row and Column Headings. (You can also get to Page Setup by clicking on the lower right corner of the Page Layout tab.) The picture of your spreadsheet will now include those headings. After printing the spreadsheet, provide your hand written signature directly below cells A28-E28. h) Print a formula page. You can show a formula page two ways. 1. Select the Formula tab and choose Show Formulas (top of formula auditing area), or 2. Press the Ctrl button and ~ buttons simultaneously. On the formula page, it is alright if some of the writing does not show completely as long as the formulas show completely. So adjust each column width so that they are narrower, but make sure the formulas in B23-D23, F23-H23, H19 and H20 (etc) show completely. To print the formula page, click on File, then Print and make sure Landscape Orientation and Fit Sheet to One Page is still chosen (as above.) Making a Graph 4. Time to make a graph of distance (y-axis) vs. time (x-axis)! These instructions will describe one way. If you know a way that is simpler or that you like better, it is fine to use that approach as long as it gets you to the correct outcome. a) Click on Insert at the top left of the page and in the charts section, click on Scatter (looks like a graph with points and no connecting lines, see right.) Choose the first chart type (again it looks like a graph with points and no connecting lines.)

4 A Chart Area box will appear in the middle of the screen. Click on the center of the area and move it off the data. b) Right click in the Chart Area box, then click Select Data in the menu that appears. When the Select Data Source box opens, click on Add under the Legend Entries (Series) in the box that appears. A new box (Edit Series) will appear. See figure at right. c) Enter a name for your ride from Greer to Gastonia. Next click on the Series X values box and select cells C5 to C13 (times) by doing a click and drag. Repeat the procedure for the Series Y values, selecting cells B5 to B13 (distance) (making sure you delete the ={1} that is present in the Series Y values box). Click OK. d) Next click Add on the Select Data Source box and another Edit Series box will appear. Use the data from the trip to Mount Mitchell (i.e. Repeat step c. using data for second trip.) In Excel 2013, the symbols for data points are initially the same for both lines. To change one of the sets of symbols, double click on one of the data points and a column will appear on the right entitled Format Data Series. Click on the paint can under Series Options. Then click on marker and on marker options. Make sure Built-in is selected and click on the box next to type. Choose your desired symbol. e) To add a chart title and axis labels, click in the center of the chart area and a plus sign should appear just outside of the upper right corner. Under chart elements, check the boxes for Axis titles and Chart Titles. Move the cursor to the chart title area on the graph and enter a title appropriate for this graph. At the end of the title, add your name. Click on each axis label box to add the axis labels. The vertical or y-axis should be labeled Distance (km) and the horizontal axis should be labeled Time (hr). (If you need to change the format of an axis (the axis scale, the number of places shown on the axes), you can bring up the editing boxes you need by right clicking directly on the axis.) f) Obtain a trendline for each of your series. Right click on one of the data points for one of the trips. A box will open up; click on Add Trendline, which will open up a larger box on the right. As you scroll down the box, make sure Linear and Automatic are chosen. At the bottom of the box, check Display Equation on chart and Display the R-squared value on chart. Repeat for the other set of data. Displays will appear on your graph that contain an equation for the trendline and the R 2 value. (The R 2 value, or correlation coefficient, is a statistical parameter that tells you how well the data points fit the line. When R 2 = 1, the fit is perfect. In other words, when R 2 = 1, the data points lie exactly on the line.) Arrange the display boxes so it is clear to the reader which set of information belongs to each line. (Note, one or both of the trendlines may intercept the y- axis below zero, so the minimum value on the y-axis may be negative. That is OK.) g) In this class we will want to have the slope and R 2 expressed with three significant figures. To obtain the correct number of significant figures, you must change the number of places displayed in the trendline equation. To do this, right-click on the trendline equation, and select the Format Trendline Label to adjust the number of places displayed. A simple way to insure three significant figures is to choose scientific and two decimal places. (To the computer, this means two places after the decimal point.) h) Before printing, we want to move the graph to a separate page. Click the center of the graph, and the Design and Format tabs appear above. Under the Design tab, select the Move Chart Location option (far right icon) and save the graph as Chart1. You can now access the chart or the data from the tabs at the bottom of the screen.

5 Distance (km) 5. Using the information from your trendline analysis. a) Your average speed for the entire 1st trip can be obtained from the trendline equation. The trendline equation is in the format: y = mx + b (where m = the slope & b = the y intercept) The slope is the change in y divided by the change in x. It is the rate of change in the line as you scan from left to right across the graph. Because distance is plotted on the y-axis and time is plotted on the x-axis, the slope (or distance divided by time) is the rate you are traveling or the speed. The units (km/hr) are consistent with this. b) Save a copy of your exercise. (One way to save your work is to first save it to the desktop, then the file to yourself. Things left on the desktop when you exit the computer are gone!) To complete this exercise: 1) Print a copy of your graph, spreadsheet and formula page. For printing your spreadsheet and formula page, see steps 3 (f) and (g), above. 2) Make sure your graph is reasonably sized, scaled correctly (see below), that the axes are labeled (with units in parentheses) and that the graph title includes your name. 3) Answer the questions on the following page. 4) Your report includes: a) spreadsheet, (b) the formula page, (c) the graph, and (d) the answers to questions on the next page in this order!!! Staple these pages together. Additional comments on graphing. Make sure your graphs are of an appropriate size to be clearly read. If there is only one graph being displayed on a page, make the graph fill the page. If you are displaying two are more graphs on a page, adjust the layout so each graph is as large and as easy to read as possible. In addition, the data points shown in the graph should fill the space in the graph. If they do not, adjust each axis scale so the data does fill the area of the graph! Make sure you have a title for your graph that includes your name. Also label the axes appropriately. When labeling the axes, units are given in parentheses. On a graph showing a linear relationship, you should add a trendline labeled with the equation defining it and the R 2 value. This trendline label should be adjusted to have three significant figures. Important Stuff: 1) Remember when the computer expresses numbers that are in scientific notation, it uses the symbol E in place of x 10, with the power of 10 listed after the E. 2) In the graph on the right, the equation for the line y = 1.13E+01x E-02, would be hand written as y = 1.13 x 10 1 x 5.54 x ) The slope, 1.13 x 10 1 km/hr, is the overall speed (rate) of the bicyclist Bike Trip Part II: The Adventure Continues, Alice Jones y = 1.13E+01x E-02 R² = 9.99E Time (hr)

6 Distance (km) Questions Sec: Name: Questions 1-5 are about your spreadsheet and graph. 1a. Define speed in terms of distance and time. b. Write the slopes and R 2 values from the graph for the two trips in the blanks below. Slope R 2 value Trip to Gastonia Trip to Mt. Mitchell c. Use your trendline equation for the Gastonia trip to calculate how long (time) it would take to bike to Newberry, SC (assume 89.5 km) under the same conditions (show calc below). (Hint: Is distance, the y or x variable?) 2. What is the statistical parameter(s) on the graph that would tell you how well the data points fit the line? 3. From visual inspection of the graph, which trendline fits the points most closely, the trip to Gastonia or the trip to Mt Mitchell? 4. Do the data points plotted for the trip to Gastonia show a linear or non-linear relationship between distance traveled and time? How about for the Mt. Mitchell trip? 5. Looking at the data for the Mt. Mitchell trip, on which part of the trip did you bicycle more slowly? How can you tell? 6. In the graph on the right is the speed throughout this trip more constant during January or April? What values shown on the graph support your answer? Seasonal Effects on a Bike Trip, Jo Rice y = 1.24E+01x E+01 R² = 9.24E-01 April Trip January Trip 7. What is the rate or speed of the January Trip? April Trip? y = 1.08E+01x E+00 R² = 9.94E Offer a possible explanation for the difference in speed for the two trips Time (hr)