Ice Melt

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Try the following related lab called "Ice Melt"

Student Handout (pdf)     Student Handout (word)

Teacher Handout (pdf)      Teacher Handout (word)

Introduction

Before the days of the microwave my mother would soften (not melt) butter using a metal pan. She would place the butter in the pan and use a spoon to mix the butter. On many occasions I asked her why she always used a metal pan and never a bowl made out of wood or plastic. She would explain that the metal surface seemed to soften the butter faster, but she was not sure why. She would then show me that the butter did not soften as fast in a plastic or wood bowl.
     Being only 4 or 5, this natural phenomenon puzzled and amazed me. I could not understand why the butter would soften faster on a metal surface even though all of the containers were room temperature. (Watch the video)

Explanation

The phenomena of the softened butter can be explained by the Second Law of Thermodynamics, the density of materials used and the ability of the material to conduct heat. First heat will naturally transfer from a warmer body with more heat energy to a colder body with less energy until thermal equilibrium is achieved. In the above example heat will transfer from the room temperature bowl to the refrigerated butter. The rate of heat transfer is increased if the material used has a high density and a high conductibility. The metal pan had the greatest density and conductibility so the butter softened quicker than when it was placed in a bowl made of plastic or wood. 

Hints

Other factors or variables can affect the rate of heat transfer. This would be an opportunity for your students to use the scientific method to explore some of these. Some of the other factors include the volume of the butter used or the thickness of the bowls used. A larger volume stores more heat energy. So a large stick of butter would require more heat from the bowl to soften. On the other hand, a thick walled bowl would have more stored energy so the butter would soften at a higher rate. The color of the bowl can also affect the amount of heat that it may have. A darker colored bowl will absorb more light energy than a shinny stainless steel bowl or a white bowl. Even though both bowls may be in the same room they may have slightly different temperatures. Any of the above examples or others that your students come up with could be used to develop a hypothesis that could be tested using the scientific method.