Windchill and Evaporation

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					                             Windchill and Evaporation

The following exercise is adapted from Graphing Calculator Activities: Exploring
Topics in Algebra I and II. (Dale Seymour Publications)

Windchill and Skin Cooling
Wind combined with cold makes temperature feel colder. Windchill is the still-air
temperature that would have the same cooling effect on human skin as a given
combination of temperature and wind speed. We can use many functions on the
calculator to generate a windchill chart that can be used for quick reference.

The equations below were derived from wind and temperature data. The y-
variable represents the windchill and the x-variable represents the actual air
temperature in degree Fahrenheit. There is a separate equation for each wind
speed. The numbers in each equation are constants for wind speed.

Wind Speed                Equation
5 mph                  y=1.1x – 4.6
10 mph                 y= 1.2x – 21
20 mph                 y = 1.4x – 38
30 mph                 y = 1.5x – 48.5
40 mph                 y = 1.6x – 52.5

Below is the table set up that we need to create:

  Wind                                 Actual Thermometer Reading (oF)
  Speed      30   25    20   15   10     5   0   -5   -10   -15   -20   -25   -30   -35   -40



    20                 -10


Calculation of Table
Set up a table in the calculator.
Go to Y=, clear all equations.
Type in the following:

Go to 2nd TBLSET, type in the window as follows:

Press [TABLE]
X is the air temperature. The Y-values are the calculated windchill values by wind
speed: Y1=5 mph, Y2=10 mph, etc. The difference here is that the table has
been rotated 90o with the X-values vertical and the Y-values horizontal.

Objectives: In this lab activity you are to:
      observe the effect of evaporation on temperature
      compare the rates of evaporation of water, alcohol, and mineral oil
      identify the relationship between evaporation and wind-chill factor

      TI-83 calculator              CBL with 3 temperature probes
      water                         alcohol
      cheesecloth or gauze          cardboard fan
      3 rubber bands


1. Wrap a piece of cheesecloth or gauze around the tip of three temperature
   probes. Secure the cloth with a rubber band just below the black tip. Place
   probe 1 into Channel 1, probe 2 into Channel 2, and probe 3 in Channel 3.
2. Press PRGM. Select Chembio. Press ENTER three times.
3. Select SET UP PROBES the press ENTER.

4. You are using three probes so select 3 and press ENTER

5. Select TEMPERATURE, and press ENTER.
   Then press ENTER, select TEMPERATURE again, this time choose
   CHANNEL NUMBER: 2. Press ENTER, then select TEMPERATURE again,
   choose CHANNEL NUMBER 3.

6. You should now be back to the MAIN MENU. Select 2:COLLECT DATA.
   Select 2:TIME GRAPH.

   Press ENTER

   Press ENTER

7. If your entries are correct, select 1:USE TIME SETUP. Press ENTER.
8. Set up the next screen as follows:
9. Press ENTER. After one or two data points appear on the calculator
   screen, quickly place temperature probe 1 in water and temperature
   probe 2 in alcohol. Then immediately remove them from the liquids and
   shake off any excess liquid. Temperature probe 3 is the control and
   therefore should be left in air. After removing the probes from the 2 liquids,
   the fan all three probes equally with a piece of cardboard. Make sure that the
   control remains dry. After two minutes the CBL will read DONE. The
   calculator will read:

       Press ENTER and your graph will appear.

10. The calculator will show a legend for the graph that contains your data. Press
    ENTER to see a graph of your data.
11. Record your initial and final temperatures for each probe in your data table.
    You can access this data on the graph by pressing the blue up or down
    arrows to change between the 3 lines then using the right and left arrows to
    along the line. You can also access the data in L2, L3 and L4. Press ENTER


                                                         Choose 4:VIEW DATA

To get to your list, follow the directions on the next screen, press STAT, then

                         DATA TABLE 1

Probe 1 - water      Probe 2 -alcohol      Probe 3 - control
initial      final   initial       final   initial        final
Sketch your graphs using the legend listed below.


 Temperature                                                  water     ___
   C                                                         alcohol   ----
                                                              control   xxxx

                             Time sec

Questions and Conclusions:
1. Which probes had a temperature decrease when fanned?
2. Describe why the temperature decreased.
3. Explain the why the control probe behaved as it did.
4. The opposite of windchill is the heat index that is defined as how hot the air
   actually feels because of a combination of high temperature and high
   humidity. What process is not taking place during times of high heat indices
   during the summer months? ___________________________
Teacher Notes:
1. The graphs (TI-83 and Graphical Analysis) below illustrate typical data collected from this
   experiment. Sometimes the beginning temperatures are not the same. You can expect the
   probes to have slightly different readings. This difference may also be due to not allowing all
   3 probes and liquids to reach room temperature. When you repeat the experiment, allow
   time for the probes to warm backup to room temperature.

Graph from TI-83




Graph from Graphical Analysis

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