8A70.80 - Red Hot Ball - Planetary Temperatures

Code Number:
Demo Title:
Red Hot Ball - Planetary Temperatures
Planetary Cooling, Radiant Energies, Kinetic Motion, Distribution of Mass
Area of Study:
Metal Ball on Rod, Stand and Rod Clamp, Bunsen Burner, Insulated Gloves, Matches, Metal Pan, Camera and Power Supply, Oxy-Acetylene Torch, Red-hot metal, Bunsen Burner, Matches, Insulated Gloves, Metal Pan.

This demonstration must be started about 10 to 15 minutes before the time to be shown.  Heat the ball with the Bunsen burner until it reaches a visible red hot.  Focus the camera onto the ball with the iris all the way open and the color balance set about halfway towards the red end.  Shut off the room lights and remove the flame and observe the cooling process.  Note the lines and spots that develop showing how the cooling rates differ in different region according to the structure and stresses on the sphere.  When the ball is no longer glowing visibly it can be shown that there is still a great amount of radiating energy by touching an unlighted match to the ball and watching it burst into flames.  The Oxy-Acetylene torch will heat the ball up much faster, however you must be careful as there is the danger of actually melting the ball.

The new CCD cameras are very IR sensitive.  Even after the ball has quit visibly glowing in the dark room the CCD camera will be able to see the ball very well.  We also have an infrared viewer that may be used for viewing the ball after it has stopped visibly glowing.

Take the metal strip and hold the end in a Bunsen burner until red hot.  Turn out lights and let cool while observing visible radiation.

  • Michael LoPresto, Nichole Hagoort, "Determining Planetary Temperatures with the Stefan-Boltzmann Law", TPT, # 2, p. 113, Feb. 2011.
  • Raymond Pierrehumbert, "Infrared Radiation and Planetary Temperature", Physics Today, January 2011, p. 33.

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