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Wind Chill!!!

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Author Contact Information

Linda Wygoda
Sam Houston High School
Lake Charles, Louisiana
wygoda@tea.rice.edu

Overview
In this activity students use a variety of windchill charts to determine how cold the temperature "feels" versus how cold it really is. Students experiment with cooling due to evaporation versus cooling due to evaporation enhanced by wind. Students tie their knowledge of wind chill to understanding the impact of cold and wind in the polar environment and prevention of dangerous conditions.

Students will:

  • predict the relationship between wind, the actual temperature and the "apparent temperature" felt by living things

  • conduct an experiemt designed to explore the relationship between these variables

  • graph and present their findings

  • predict and explore how this phenomenon impacts living in polar regions;

  • suggest measures that can curtail the impact

    Grade Level/Discipline
    Grades 9-12, Earth Science, Meteorology

    National Standards

  • Content Standard B: Interactions of Energy and Matter
  • Content Standard D: Energy in the Earth System

    Pre-activity set-up

    Materials

  • two temperature probes
  • squares of filter paper
  • small rubber bands
  • beaker of water at room temperature
  • Computer-Based Laboratory (CBL) (optional)
  • string
  • ringstand
  • indexcard
  • stopwatch
  • graph paper
  • colored pencils

    Time Frame
    1 class period

    Engagement and Exploration (Student Inquiry Activity

  • Ask students to hypothesize about what happens to water temperature as the water evaporates in a windy situation? In a "wind-free"environment?

  • What will the temperature curve will look like when water evaporates with no wind? Have students make a graph to predict the effect of wind on temperature. Temperature should be on the Y-axis and time on the X-axis. A line should be drawn to represent how temperature changes over time

  • What the temperature curve look like when water evaporates with a large wind? Have students make a graph to predict the effect of wind on temperature. Temperature should be on the Y-axis and time on the X-axis. A line should be drawn to represent how temperature changes over time.

  • Explain to students that that they will test their hypothesis using the temperature probe and CBL system. See student handout for directions on using the equipment

    Explanation (Discussing)

  • The effect the students experienced is called "wind chill." Wind chill makes you feel colder on windy days than on calm days of the same temperature. Wind cools because it blows away a thin layer of warm air that normally surrounds our bodies. THe wind also draws away heat by quickly evaporating any moisture that forms on our skin. Often "wind chill" is presented as a more accurate measurement of outdoor temperature than the actual temperature. The wind chill index describes the equivalent temperature for which the heat loss from exposed skin would be the same if the wind were near calm. Inanimate objects, such as cars, do not "feel" wind chill. Water will not freeze until the temperature reaches freezing - no matter how hard the wind is blowing.
  • What factors, other than temperature, determine how "chilly" you feel?

  • Ask the student groups to use the wind chill graphs to find the wind chill equivalent temperature for each of the following: A. On a cold day on your way to school, the air temperature is -7 C (20 F) and the wind speed is 15 mph B. The air temperature is -20 C (-5 F) and the wind speed is 20 mph C. The air temperature is 2 C (35 F) and the wind speed is 25 mph

    Image from Gene's Measurements and Weather Page, http://ourworld.compuserve.com/homepages/Gene_Nygaard/windchil.htm, 26 December 1997.

    Image from Gene's Measurements and Weather Page: http://ourworld.compuserve.com/homepages/Gene_Nygaard/windchil.htm, 26 December 1997.

    Image from Winter Weather Page, NOAA, National Atmospheric and Oceanic Administration: http://www.crh.noaa.gov/cys/wndchill.htm, 26 December 1997.

    Elaboration (Polar Applications)

  • Use the Teacherís Experiencing Antarctica and the Arctic Web Page to research the journals of teachers who have visited the polar regions. What entries do they make about the weather. Find an entry that describes weather conditions that the teacher/researcher expereienced. How did the weather impact their activities?

  • Why do polar researchers take the temperature and wind chill so seriously? What causes frostbite and hypothermia? How might wind chill influence the onset of these conditions? What precautions might prevent these conditions?

  • Investigate how wind chill charts are made by using some of the internet sites in the backgroun information and resources. Examine the variables in the NWS wind chill equation. What variables impacted student experiments.

  • Investigate Paul Sipleís experiments in Little America, Antarctica on wind chill.

    Exchange (Students Draw Conclusions)

  • What did the graphs look like? What was the effect of the wind on the temperature?

  • What variables affected their graphs? Possible answers might include the temperature of the room, the starting temperature of the water, the amount of water, the wind speed and direction.

  • Why are these graphs cooling graphs not heating graphs? When water evaporates it removes heat from the surrounding environment. This occurs because the water molecules must gain sufficient kinetic energy to escape the polar bonds between them.

  • What might happen if you did a similar experiment with an alcohol instead of water? Alcohols do not have the same amount of polar bonding as water, so it takes less kinetic energy for them to evaporate. Because of this, alcohols evaporate much more quickly than water. Therefore, when comparing equal amounts of water and alcohol, the alcohol will evaporate more quickly and remove more energy (i.e. heat) from its surroundings.

    Evaluation (Assessing Student Performance)
    Students can be evaluated based upon their parcticipation during the lab experiments and class discussions, the completion of lab data tables and graphs, and their answers to written discussion questions.

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