Why is the Earth Still Hot Inside?
https://serc.carleton.edu/spaceboston/2010activities/46734.html


In this activity developed by Aaron Keller, students learn about heat transfer as a function of the size of the object. Students heat various sized marbles or spheres, record temperature change across the items, and analyze their data. They observe that the rate of heat transfer is directly proportional to the surface area but inversely proportional to volume. Students gain proficiency in using lab equipment to make repeatable measurements.

This resource is referenced here: