Scatterplots
Build a Bridge!
✔ Reflection 1 |
Write about your experience (and skill!) at the bridge building game. What strategies worked? What strategies didn't work? Did you ever run out of funds?
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✔ Discussion 1 |
Do you think civil engineers deal with the same kinds of issues?
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While the design and construction of civil engineering projects such as bridges are important, an engineer still has to source and purchase the materials for the project. Engineering crews can bid for the materials and labor from contractors. Analyzing the cost history and unit price of a certain material helps engineers determine how much to bid. Generally, the more of a material you purchase, the lower the unit price will be.
Scatterplots
✔ Notes 1
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A scatterplot has points that show the relationship between two variables, graphed as (x,y) ordered pairs.
The independent variable, or causative variable, goes on the x-axis. The dependent variable, or affected variable, goes on the y-axis. |
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If the data points increase together, the relationship between the two variables has a positive correlation.
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If the data points decrease together, the relationship between the two variables has a negative correlation.
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If the data points show no apparent relationship, there is no correlation.
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Construction Cost History
The following table is a selection of the excavation cost history from the Pennsylvania Department of Transportation. Each data entry gives the date a sale was made, the amount of material the contractor bid for, and the final cost per unit paid. Engineers analyze entire spreadsheets of this data to determine trends and decide how much to bid for a certain material.
Try It!
✔ Figure 1 |
A selection of the cost history of guide rails is given below. Construct a scatterplot of the guide rail cost history with amount as the independent variable and cost as the dependent variable.
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✔ Analysis 1 |
Determine if the guide rail cost history has any correlation.
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✔ Figure 2 |
A selection of the cost history of road signs is given below. Construct a scatterplot of the road sign cost history with square feet as the independent variable and cost as the dependent variable.
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✔ Analysis 2 |
Determine if the road sign cost history has any correlation.
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Line of Best Fit
✔ Notes 2
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A line of best fit is a linear trend line that goes through as many data points on a scatterplot as possible. Approximately half of the points should lie on each side of the line of best fit.
We can determine the equation of the line of best fit using slope-intercept form. |
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Try It!
✔ Figure 4 |
Using a ruler, draw a line of best fit through the guide rail cost history scatterplot.
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✔ Analysis 4 |
Determine the equation of the guide rail cost history line of best fit using slope-intercept form.
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✔ Figure 5 |
Using a ruler, draw a line of best fit through the road sign cost history scatterplot.
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✔ Analysis 5 |
Determine the equation of the road sign cost history line of best fit using slope-intercept form.
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An Interview with a Civil Engineer
I'm doing things that affect people on a daily basis. I build airports, or at least I make sure that the pavement is good and that planes can actually land on the runway... Civil engineering is all related to society: If we don't design the drainage well, it will flood and people are going to get really upset. If I do it right, nobody notices; but if we do it wrong, everybody's going to notice.