The Newton's Law of Cooling model computes the temperature of an object of mass M as it is heated by a flame and cooled by the surrounding medium.  The model assumes that the temperature T within the object is uniform.  This lumped system approximation is valid if the rate of thermal energy transfer within the object is faster than the rate of thermal energy transfer at the surface.  Users can select the mass or volume of the object and the type of material, and the model computes the temperature as a function of time. The model plots this temperature as a function of time as the user heats and cools the object.  It is a supplemental simulation for an article by William Dittrich in The Physics Teacher (TPT).  

The sphere heats and cools by exchanging thermal energy with the surrounding fluid by convection and this energy exchange is proportional to the difference between the sphere's surface temperature Ts and the temperature of the fluid Tf.  Inside the sphere the thermal energy is transported by diffusion.   The temperature inside is uniform if thermal energy transfer within the sphere is faster than thermal energy transfer at the surface.

The simulation shows how a temperature gradient appears if the heat transfer coefficient or the transfer coefficient are large.  The Heating and Cooling a Sphere model allows users to select copper, aluminum, and iron material properties and to set the sphere's radius and its heat transfer coefficient to observe these effects.

The Heating and Cooling a Sphere model was created using the Easy Java Simulations (EJS) modeling tool.  It is distributed as a ready-to-run (compiled) Java archive.  Double clicking the ejs_heat_HeatingAndCoolingSphere.jar file will run the program if Java is installed.

Please note that this resource requires at least version 1.5 of Java.