Physical Principles: Thermal expansion

Student Prerequisites: For this demonstration, students are recommended to be familiar with the following concepts – a.) temperature as a measure of hotness and coldness, b.) heat which refers to energy transferred due to a temperture difference; c.) also an understanding of harmonic oscillators is helpful for a microscopic explanation of this demo.

Introduction: Most materials expand when their temperatures increase by heating. In this demo, we attempt to verify this effect of heat on materials, particularly metals, through a little tricky experiment. Students will be asked whether heating the copper ring would allow the ball to pass through it.

Description of the Demo: Many properites of matter that we can measure depend on temperature, e.g., the volume.  Temperature, which can be defined macroscopically, is also related to the kinetic energies of the molecules of a material. In general this relationship can be fairly complicated. Thermal expansion can be understood qualitatively on a molecular basis. For crystals, namely, homogenous solids formed by a repeating, three-dimensional pattern of atoms, ions, or molecules and having fixed distances between constituent parts, a model of interatomic forces can be assumed to give a fairly effective explanation to thermal expansion.

Instructions: The operation is rather simple. See following picture of all equipment involved.

Note to the Instructor: Burn hazard. Make sure the ball is out of the ring before it cools.

Possible CPS Questions:

1. Can the ball pass through the ring when the latter is heated, given that the ball cannot in the beginning? [Question] [Answer]

2. Will the ring restore its original size after being heated? [Question] [Answer]

3. Decide which one of the following substances diminishes in its volume when heated? [Question] [Answer]

4. (Open question for interested students) A spring model between atoms can be postulated… [Question]