7D20.10 Mousetrap Chain Reaction


Chain reactions


A chain reaction is simulated by an array of armed mouse traps loaded with ping pong balls.



  • [42] Mousetraps in a 6 x 7 array attached to a piece of plywood
  • [1] Single mousetrap
  • [43] Ping pong balls
  • [1] Rubber ball
  • [1] Plexiglas box with a hole in the top that covers the array
  • [1] Short stick

Classroom Assembly

  1. CAREFULLY arm the mousetrap array with the 42 ping pong balls. This takes 15 minutes or longer (if traps are accidentally set off) to accomplish and must be done ahead of time.

Important Notes

  • It is very easy to set off mousetraps prematurely. Great care is required when arming the array of mousetraps, when dropping a ping pong on the array during the "unmoderated" portion of the demonstration, and when moving the array.


Nucleus/Mousetrap Analogy:

  1. Arm the single mousetrap with a ping pong ball keeping well away from the array.
  2. Taking care to direct the single mousetrap away from the array, set off the single mousetrap with the stick. The ping pong ball will fly across the lecture hall.
  3. Discuss the analogy between a nucleus and the mousetrap.

"Unmoderated" System:

  1. With the Plexiglas cover off, drop a ping pong ball onto the array. One or two traps will go off, and their balls will fly across the room.

Chain Reaction:

  1. CAREFULLY place the Plexiglas cover on the array.
  2. Drop the rubber ball through the hole. A chain reaction will occur and most traps will go off.


Additional Resources


  • PIRA 7D20.10
  • Video Encyclopedia 25-15
  • Sutton, RM, 'A Mousetrap Atomic Bomb' AJP 15, 427 (1947) (SFU microfilm) 3 or 4 dozen traps, 2 or 3 cork stoppers/trap, energy per trap estimated at 8x1E6 ergs
  • Manley, JH 'The Mousetrap Bomb: Modification N+1' AJP 16, 119 (1948) (SFU microfilm)--not useful
  • Rathgeber, HD 'Mousetrap Model of Chain Reactions' AJP 31(1) 62, 1963 traps affixed in groups to pieces of hardwood, 2 pieces of hardwood on each trap
  • Higbie, J 'The better mousetrap: A nuclear chain reaction demonstration' AJP 48(1), 86 (1980) uses electronic 'traps'


  • Don't attempt this at home!

Last revised

  • 2018


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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.