Thermodynamics, Conductors vs. Insulators (Dolly Thicke)
Title:
Heat, Conductors and Insulators
Principle(s) Investigated:
The laws of thermodynamics as they pertains to isolated systems spontaneously evolving towards thermal equilibrium, or the tendency of temperature to equalize over time in a contained environment.
MS-PS1-4. Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.
MS-PS1-1. Develop models to describe the atomic composition of simple molecules and extended structures.
Materials:
Frying pan, plastic cutting board, ice cubes, towels, thermal container for ice, provided study guide (optional). It should also be noted that identical blocks can be purchased one each of aluminum and one of plastic. This allows for a more direct comparison of the two substances and how they feel to the touch. I prefer to use real life items so that observers will feel compelled to further explore the process at home with their families. Both are great.
Procedure:
1. Hand out materials and ask what differences can be observed.
2. Ask observers for hypothesis of what will happen if we melt ice on the surface of each? Will one melt slower than the other? Remind them that you aren’t going to put the frying pan over a burner, and doesn’t the frying pan feel cool? Why won’t that make the ice melt slower?
3. Watch result. Let students decide why the frying pan melted the ice much faster than the cutting board?
4. Discuss different areas in the room where temperature may be hotter or cooler, discuss the difference if windows were covered, electricity cut off and the room left closed for the night. The answer? Every item in the room is the same temperature. So if I grab the metal doorknob will it feel room temperature to me? No?
5. Look at study guide, the second rule of thermodynamics and definition of heat? Why would the doorknob still feel cool if it’s the same temperature as everything else?
6. Describe Molecules in all forms are always in motion, and we’ve seen demonstrations of heat molecules. What do we know hot air does? Hot air…? Rises, yes but it’s also molecules spazzing out going in every direction seeking some sort of equilibrium. Hot air will move to areas of lower pressure and in a closed system, the temperature will eventually be all the same. 7. Discuss conductors vs. insulators. Is the doorknob a conductor or insulator? Why. In metal, molecules are packed very tightly allowing heat to move quickly, doing its job, equalizing the temperature of every item in the room. What about the cutting board? Just the opposite is true, molecules are not packed tightly and will not expedite the melting process.
8. As a group answer all questions about whether each item on the bottom of the study guide is a conductor or an insulator.
9. Tell embarrassing story about mule cup or give your own personal experience, ask for real life examples of how we can use this information. I wouldn’t bring my ice cubes to this presentation in a metal lunchbox for example. Creating a closed system for a picnic...etc.
Student prior knowledge: What prior concepts do students need to understand this activity? They should have already seen simulations of the way molecules act when heated. Perhaps students have done activity with laser thermometer, or you can do it simultaneously.
Explanation:
Ice cubes will melt faster on metal because metal will conduct all the heat that is around it. It doesn’t need to be placed on a burner because the air around it is much hotter than the frozen ice. The frying pan, moves those warmer molecules quickly around the ice and causes it to melt rapidly. The warmer molecules, can move through the tight molecules in the metal conducting material to attain their ultimate goal of temperature equalization. Insulating materials such as that of the cutting board is not made from tightly packed molecules but rather quite the opposite.
This presentation was designed with 8th grade physical science students in mind and so I forewent discussion on entropy. This concept would be a wonderful topic for further examination in a Chemistry class.
Questions & Answers:
- Why would ice melt faster on a surface that feels cold? Because conductive materials conduct heat. They aren’t really a lower temperature, they feel cold because they are pulling the heat away from your hand.
- Why does hot air rise? Hot air does seem to rise. If you fill a balloon with hot air it will rise into the sky, however the truth is a bit less simple than that. Hot air molecules are rapidly moving about seeking a lower pressure environment. This erratic energy will inflate the balloon and cause it to rise as the hot air molecules seek equilibrium.
- What type of container would you use if you wanted to bring ice cubes to a science project and you wanted to keep them intact? A metal lunchbox or a spongy plastic container? You would chose a spongy plastic container that will not conduct the heat around it and melt the ice.
Applications to Everyday Life:
The principles presented in this lesson are good to understand when trying to create a contained environment where the atmosphere remains at a certain temperature. I would not have wanted to bring my ice cubes to my presentation in a metal bucket for obvious reasons. I wouldn’t want to take a nap on a surface made from matter that will conduct heat away from me or in very high temperatures conduct the heat around me. We don’t want to drink hot coffee out of a copper mule cup invented with the intention of keeping alcoholic beverages cold.
Photographs:
Videos:
https://www.youtube.com/watch?v=c4KRwOyrNPw
References:
Geisen, Michael. (Ed. 1). (2016). Everything You Need to Ace Science In One Big Fat Notebook
San Francisco: Workman Publishing
Study guide follows...
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STUDY GUIDE
Part of the laws of thermodynamics state that….
Isolated systems spontaneously evolve towards thermal equilibrium.
OR, in less precise terms…
Temperature has a tendency to equalize over time.
CONDUCTORS INSULATORS
A.Metal doorknob B. Methods of teaching science book C. Frying pan D. Cutting board E. Fluffy acrylic handbag F. Metal lunchbox G. Designer bag with metal sequins and chains H. Insulated synthetic sport bag