Weather and Negative Numbers

Purpose: students will discover a meaningful application for negatives; students will use variables in a real technology based setting; students will create meaningful graphs.

Materials: Indoor/Outdoor Thermometer, Computer with Spread Sheet (eg: Microsoft Excel, Open Office Calculate)

Background: This lesson was used in an urban seventh grade to present negatives in a pre-algebra class. There was only one thermometer and one Macintosh 5200 with Claris Works available.

Written 1999

Reformatted January 2010

Method:
 Place an indoor/outdoor thermometer by the window Assign a "meteorologist" to read the temperatures daily and record them using a spread-sheet. Train the student to use columns in the spread-sheet consistently (Eg: column A: represents today's date, B represents the inside temperature, C represents the outside temperature, D represents the difference.) Train the meteorologist to use the cell variables to determine the difference (eg: '= B5 - C5 ') Each day, have the meteorologist report to the class the temperatures and the difference. (To let all students get a chance, change the meteorologist each week and have the previous one train the new one) When the temperature outside drops below the temperature inside the spread-sheet will report a negative number. At this point ask the meteorologist "What does the negative mean?" Most students will quickly recognize that the negative means that its colder outside. Once the students are comfortable with using the spread sheet add a new column for the difference between yesterday's temperature, and today's (eg: '= C11 - C10). Students should see that a negative here means the temperature has dropped. Use the spread sheet chart option to create a graph. Discuss with the students, "should the lines be falling or rising this time of year (spring or autumn)?" "Do we see that happening, why/ why not?"

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Notes:

1. The first student meteorologist can pick the order of the subtraction. They will naturally pick Large - Small. The following students must understand to use the same order.
2. This lab demonstrates negatives with temperature even in climates which stay above freezing- provided the outside temperature will dip below the inside temperature.
3. Frequently the downward slope of the fall temperatures will not be evident over the "noise" of daily fluctuations. This can lead to a lesson on moving averages.
4. If the students picked 'Inside - Outside' the difference column will rise while the outside temperature falls. A rising graph resulting from falling data might lead to a discussion of counter-intuitive results.
5. One way to insure order has been maintained in the difference column is to use the copy & paste functions.