4A30.21 Ball and Ring


Thermal expansion


When the ball is heated with a blowtorch, the ball expands so much it no longer fits through the ring.



  • [1] Ball on a stick
  • [1] Ring on a stick
  • [1] Blowtorch
  • [1] Lighter
  • [1] Ball holder

Important Notes

  • Be careful with fire and hot items. Perform the experiment away from flammable objects, if possible.
  • Make sure you shut off the gas completely when turning off the blowtorch.


  1. Show that it is easy to put the ball through the ring.
  2. Light the blowtorch and heat the ball evenly, waving the flame over all parts of the ball.
  3. Turn off the blowtorch.
  4. Show that the ball no longer fits through the ring.
  5. Place the ball on the metal holder so that nothing can be damaged by the hot ball.


Additional Resources


  • PIRA 4A30.21


  • Don't attempt this at home!

Last revised

  • 2019


  • Putting the ring in dry ice also works, though it warms up rather quickly. If using dry ice, beware of its hazards, including frostbite, CO2 poisoning, and embrittling of materials.

Related AV

Related demos


If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.