Checking Temperatures

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Objective

SWBAT explain why you cannot trust your senses when measuring temperatures.

Big Idea

The heat conductivity of different materials can be measured qualitatively.

The Need for the Lesson

It is easy to rely on your senses to evaluate temperatures of different surfaces but it is not an accurate way of measuring it. 

Heat transfers from areas of higher temperatures, your fingertips, to areas of lower temperature, the objects at room temperature. What makes one material feel cooler than another is the rate at which the heat transfer occurs - thermal conductivity.

This is a discrepant event for students. Many students make an incorrect prediction as to which material will melt the ice faster, even after knowing the temperatures.

Investigation Preparation & Summary

10 minutes

Students make predictions based on their senses (touch) to rank the materials from coldest to warmest. Based on their rankings, students predict which material will melt the ice fastest. (MS-PS4-2 Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials.) (SP3 Planning and Carrying Out Investigations

This is a discrepant event for students. Many students will make an incorrect prediction and will rethink their ability to judge temperature by touch when examining the evidence. (SP7 Engaging in Argument from Evidence)

The longest timeline for this project is the preparation of materials for each student group. 

In 2007 the American Physical Society produced PhysicsQuest 2007: Marie Curie’s Floating Classes. Originally the activities were introduced as part of a contest. I modified the materials to remove references to the contest and changed the format to fit into my students' science journals. A few minor changes were also made to accommodate the learning needs of my students or materials I had on hand. The American Physical Society continues to publish annual challenges. Please visit their website.

Staff, P. (2007, January 1). Physics Quest Marie Curie's Floating Classes. Retrieved February 23, 2015, from http://www.physicscentral.com/experiment/physicsquest/upload/pq07-manual.pdf

Turn, Talk & Record

5 minutes

Turn/Talk/Record

Turn, talk and record is a strategy I use at the beginning of most lessons involving lab work. The strategy is designed to help students focus on today's lesson.

Students turn and talk to their elbow partner. This is the student sitting next to them who will be their partner for this lesson. Students are responsible for recording in their journal a summary of their discussion.

Today students will be talking to their partner and recording responses to the following questions:

    1. Touch some of the things around you - like your desk, your skin and the chair. Which feels the warmest? Which feels the coldest?
    2. What are some examples of how people judge the temperature of something by touch?
    3. On a scale if 1-10, how much do you trust your ability to tell the differences between hot and cold objects
    4. One-by-one, touch each piece of material for about 2 seconds. Then rank the from coldest to warmest. 

Students are ranking glass, cardboard, felt and metal

            • __________ Coldest
            • __________
            • __________
            • __________ Warmest

 

How do I develop routines and procedures to support students to work independently in the science classroom?

 

The Classroom Video: Turn - Talk - Record explains the Turn/Talk/Record strategy, how students use the strategy in this lesson, why I selected the strategy to use in this lesson and why it was successful.

Share-out to Check for Understanding

5 minutes

Share-out to Check for Understanding

Before we continue, I stop students and ask them to share out their answers. This mini formative assessment allows me to make sure that students are on track.

 

How do I develop routines and procedures to support students to work independently in the science classroom?

In this Classroom Video: Share - Out to Check for Understanding you will see students sharing their answers from Turn/Talk/Record. I explain the strategy, why it is a successful and important element of today's lesson.

Consult the Experts

10 minutes

Consult an Expert

How does an infrared thermometer work anyway?  If I have students in class who work on cars, they can explain how they use infrared thermometers to check the heat of car parts. It really does take a village to educate students. This video lets students hear different voices, they are “consulting with experts” and they see that what we are doing has a connection to the real world.

 

How can I develop a classroom culture that encourages student engagement, curiosity, and a desire to understand the world through scientific investigation? 

 

The Classroom Video - Consult the Experts explains the strategy and how it successfully meets the needs of students in this lesson.

Creating a Discrepant Event

15 minutes

Creating a Discrepant Event

Before class, I prepared a bowl of ice. Some of it has melted so I now have a mixture of ice and water.

What temperature do you think the ice and water will be when I use the infrared thermometer to measure it?  The students predict temperatures between 30 and 40 degrees.

The infrared thermometer actual measures 34 degrees. This established credibility with the students that the infrared thermometer actually works. 

Using an infrared thermometer, I  measure the temperature of the lab materials. We find that the materials - felt, metal, cardboard and glass are all actually nearly the same temperature. Cardboard is 74.1, felt 73.7, metal 74.5 and glass 73.2 degrees Fahrenheit. They are all around room temperature.

Notice that we are using degrees Fahrenheit. My students are going to be grappling with unexplained results when their ice melts first on the metal and glass and last on the felt and cardboard. While they are actually pretty good at comparing temperatures in Celsius, I did not want to further complicate the analysis for them by using Celsius. Instead I selected a scale they were most familiar with for comparison.

Student express some disbelief that the temperature of all the materials - metal, glass, felt and cardboard are nearly the same. They are still convinced that they can best judge the temperature of the materials using only their sense of touch.

I tell the students that I will be giving them ice cubes. The ice cubes are to be placed one on the center of each of the materials - felt, metal, cardboard and glass.

Do you think the ice will melt at different rates on each of the materials? Yes.

Where will we see the ice melt first?  Student predictions include the felt and cardboard because they feel warmer.

I no sooner distribute the ice cubes then I hear a group of students begin talking excitedly. It seems that the ice is already melting on the metal and not on the felt or cardboard. 

Some students are convinced that the felt and cardboard ice cubes are actually melting but they cannot see it so I ask them to lift the ice cubes to check for melt underneath. They find none under the felt and cardboard after the first minute. 

A minute later students again express concern that they simply cannot see the the melt on the felt. I gently explain to them that if the cardboard or felt was wet, we would see some change in color. The felt and cardboard would be darker when wet.

Student Observations

Ice melt is designated by the shading in the drawing

Students continue through the lab, responding to question prompts and reading about the property of the materials' call heat or thermal conductivity. Heat flows through metal or glass faster than through the other sample materials, felt and cardboard.

As I circulate around the room, I ask students if they have an explanation for the order of melt. Some students suggest it is the texture or if the material reflects light. Later they will answer questions that will lead them to understand the difference is heat conductivity.

How do I support students to persevere and grapple with complex tasks?

 

The Classroom Video: Discrepant Event explains why creating a discrepant event for students is a successful strategy for new learning. The students are experiencing cognitive dissonance - what they thought they knew and their observations are not in sync.

Connecting the Learning

10 minutes

Even adults struggle with the concept of heat transfer, this is why measuring tools are so important. The students are amused by the Misconceptions About Temperature video. They like the English pronunciation of aluminum!