Can our fingers be good thermometers? [back]

Key Learning Points

  1. Temperature as a measure of hot and cold
  2. Temperature measurement

Teachers' notes: (zip 11k)

Typical results, suggested answers, students' worksheet.


Video sample

One way to explore the subjectivity of human temperature sensation.
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Introduction

You may have the experience that after placing your hand in ice water for a while, tap water, which ordinarily feels cool to your hand, feels warmer than usual. During a fever when you use an ice pack to cool your forehead, the ice pack feels cold at first; but after a while, the sensation of coldness is no longer so strong.

The above experience shows that our sensation of hot and cold is rather subjective and cannot be trusted as a temperature measurement. In this activity, students are going to experience hot and cold sensation with their fingers and discover how subjective their sensation towards temperature can be.

Caution: As this experiment involves the use of hot water, students must exercise care when handling hot water to avoid scalding themselves or others. Students who feel discomfort when performing the experiment should stop immediately.


Apparatus

Three beakers, thermometer, supply of hot water, supply of room temperature water, supply of ice, stirrer, stopwatch.


Procedure

  1. Several students form one group. Each group is given three beakers lined up on the table. The first breaker is filled with warm water at about 45 , the second one with water at room temperature, and the third one with ice water at 0 .
  2. The student dips his/her left index finger into the beaker of warm water and his/her right index finger into the beaker of ice water simultaneously for around 10 seconds.
  3. Then place both fingers into the beaker of water at room temperature, and compare the sensation on the fingers. Record any difference in temperature sensation on the worksheet.
  4. Repeat the experiment by reversing the role of the two fingers.
  5. Let each student do the experiment. They will then discuss the result in the group.

Discussion

  1. How do your fingers feel when they are placed in water at room temperature for both trials? What does this tell you about our senses towards temperature measurement?
  2. Compare your outcome of the experiment with those of your group or the rest of your class. Do their results point to the same conclusion as yours?
  3. If you do not have a thermometer, how accurately can you determine the temperature of the water in the beakers with your fingers? Can you tell with your fingers that the temperature of the warm water is more than 40 higher than the temperature of the ice water?
  4. Apart from the fact that your sensation towards temperature is subjective, can you use your finger to measure a temperature of around 100 without risking injury? Can you measure a temperature much lower than 0 without risking injury? You must have heard of burns caused by high temperature, but have you heard of terms like cold burns or frostbites?
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