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The acrobat donkey

The acrobat donkey
Materials and mounting
instructions:
  a cork, four wood matches, a piece of cardboard shaped as the head of a donkey, a piece of wire shaped as a half -loop, a heavy nut. Fix to the cork the cardboard head, the four matches as hooves and the wire as tail of the toy donkey.
How to play:   normally the toy donkey needs to stand on its four hooves to remain in equilibrium, but, if one hangs to the end of the wire the nut keeping it below the body of the toy donkey, it will remain in equilibrium on its back hooves, as in the picture.
Physics:  
  • force and interaction: the gravity force is characteristic of the interaction which would make the toy donkey fall,
  • the gravity force has the direction of the vertical line,
  • when the toy donkey rests on its four hooves on a support plane, the support applies an upward force which keeps it in equilibrium,
  • this happens because the vertical line through the barycentre passes within the four points of support of the hooves,
  • by hanging the heavy stud nut to the end of the wire, the gravity force of the nut has the effect of shifting the overall barycentre below the support points: the donkey can now remain in equilibrium on the back hooves,
  • around this position, the donkey can oscillate with a regular periodic motion.
Educational aspects:  
  • discover force and interaction and different types of forces (Fa),
  • discover direction of forces (Fc),
  • analyse the relation between equilibrium and support surface (Fe),
  • discover how to change the barycentre to maintain the equilibrium (Fe),
  • observe the periodic motion of oscillation around the equilibrium position (Se),
  • compare with your expectations.
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Last modified: Thu Nov 16 09:22:55 CET 2000