Boiling water in a paper cup

Relevant Resource questions :

Concepts demonstrated :

• Heat transfer by conduction.
• Thermal conductivity.

Equipment needed :

• Equal lengths of wood and metal rods joined together
• paper wrapped tightly around the wood
• bunsen burner and matches
• CCD camera (optional)

• Wrap paper tightly around the wood and around metal rod.
• Place the rod over a bunsen flame at the junction of the wood and the metal.
• Wait a few seconds for the paper to char.

None.

Physics involved :

Heat transfers quickly through the paper because it is thin and therefore does not burn due to the applied flame. The metal conducts the heat away from the junction and therefore remains cool. The wood however does not conduct very well and therefore rapidly heats up burning the paper, and the wood underneath if left too long.
Burn marks may be seen along the length of the wood in the direction of the grain of the wood. This is because the thermal conductivity of wood is better along the grain of the wood.

How to use the Demonstration :

• Use as a POE demonstration to explain thermal conductivity.
• Describe the experiment to the experiment to the students "The dowel is flush against the metal rod, and paper is wrapped around the midpoint or join".
• Ask the students to predict the result when a bunsen flame is applied to the paper.
• Perform the experiment and observe that the paper chars on the wood side and remains uncharred on the metal side.
• Ask the students to explain the result.

• Loose flowing versus tight fitting clothing (of the same material).
  Q What is the difference in the ease of which the two would catch fire?

Other Comments :

• Examine the preconceptions the student's have regarding fire being able to burn paper. Show that it is not necessarily the case that applying fire to paper causes it to burn.
• Develop this demonstration pedagogically (teacher/child interation versus teacher/adult) which would be very effective. This is a somewhat advanced concept.