Investigation H2: Telling Hot from Cold

Transcription

1 Investigation H2: Telling Hot from Cold Instructor Note: The following activities deal with the ambiguity of using the words hot and cold when describing temperature. The necessity of using a thermometer should become apparent from these observations.

2 21 Activity H2.1: Is it hot or is it cold (Laboratory Activity) Equipment: A container of warm, a container of cold, and a container of room temperature water. The purpose of this Demo/Discussion is to show how words like hot and cold are relative. Have one student place a finger in some fairly hot water (don't tell the student that the water is hot) and another student place a finger in some fairly cold water (again, don't tell the student that the water is cold). Have each describe how it feels to have their finger in the water. Have each then place the same finger in a common container of room temperature water. Again ask each to describe how this feels. Students must begin to recognize that the sense of touch is not a reliable indicator of temperature. 1. WHAT S YOUR IDEA You will place one finger in some fairly hot water and another finger in some fairly cold water. Then you will put both fingers in room temperature water. What do you think you will feel 2. WHAT ARE THE GROUP S IDEAS Compare your predictions with those of others in your group. Students should discuss the words used to describe temperature -- hot, cold, and room temperature. 3. MAKING OVSERVATIONS: Complete this activity. Describe what you feel. 4. MAKING SENSE: Account for the differences in what you feel. Students should recognize that the sense of touch is not a reliable indicator of temperature. H2.1(1) Instructor Materials 2001 American Association of Physics Teachers

3 22 Notes H2.1(2) 2001 American Association of Physics Teachers Instructor Materials

4 23 Activity H2.2 : Can you tell hot from cold (Laboratory Activity) Equipment: Cups of various materials (plastic beads, glass beads, copper shot, steel shot, beans, popcorn, styrofoam, rubber washers), sets of flat plates of metals, wood, slate, paper, etc., and thermometers. Cups of Beads Activity Begin by using cups of beads made of plastic, glass, Styrofoam, or copper (all of which are at the same temperature probably room temperature). Before the students are allowed to touch the beads, ask them to predict the temperature of each material and physically arrange them from warmest to coldest. Next, have them lightly touch each and do a fresh ranking as to temperatures from warmest to coldest. Students will note discrepancies in the two rankings. Obtain a cup of each kind of bead without touching the beads. 1. WHAT'S YOUR IDEA Rank order the beads from the warmest to the coldest. 2. WHAT ARE THE GROUP'S IDEAS Compare your predictions with others in your group. 3. WHAT DO YOU FEEL Touch the beads now and rank order them from warmest to coldest. How did this order compare to your prediction Compare with others in your group. 4. EXTENDING YOUR OBSERVATION: Measure with a thermometer the temperature of each cup of beads. Again rank order from warmest to coldest. The temperature of the beads should then be measured with microcomputer based lab (MBL) probes or thermometers. The students must then compare their fingered results with the instrumentally measured results. Hopefully, the temperatures of the beads will be the same. Compare the last two rankings (fingers vs thermometers) and discuss the results within your group. 5. MAKING SENSE: What generalization could you make As already noticed in Activity H2.1, touch is not necessarily a good indicator of the actual temperature of an object. Students should realize that all the H2.2(1) Instructor Materials 2001 American Association of Physics Teachers

5 24 materials touched are at room temperature. The concept of equilibrium temperature may be developed. Flat Plate Activity A second activity (optional) can involve an array of materials made into large flat plates. These could be copper, Styrofoam, wood, slate, aluminum, paper, etc. Students would touch each of these and agree that there again seemed to be temperature variations but recognize, as with the beads, these are in fact at the same temperature. Observe the plates. Without touching them, rank their temperatures. 6. WHAT'S YOUR IDEA Rank them from the warmest to the coldest. 7. WHAT ARE THE GROUP'S IDEAS Compare your predictions with others in your group. 8. WHAT DO YOU FEEL Now touch the plates and rank order them from warmest to coldest. How did this order compare to your predictions Compare the results with others in your group. 9. EXTENDING YOUR OBSERVATIONS: Measure with a thermometer the temperature of each plate. Again rank order from warmest to coldest. 10. MAKING SENSE: Compare the last two rankings (touch vs thermometers) and discuss the results within your group. Compare these results with the bead results. The main purpose of this final activity is to strengthen the student view that touch is not a reliable thermometric procedure. Many of the students will recognize this before they begin touching these plates. Other students will cling to small temperature differences arising from variations in the equipment and sustain their early belief that there is a clear ranking by touch. H2.2(2) 2001 American Association of Physics Teachers Instructor Materials