PURPOSE: To demonstrate the solution to the famous "hourglass problem," or Galileo's water bucket.

DESCRIPTION: An hourglass with its sand has a weight W when at rest on a scale as photographed. Before time t=0 the sand is held in the top of the hourglass by an invisible massless membrane. At time t=0 the membrane is removed by a massless d emon, allowing the sand to fall into the bottom of the hourglass. At time t=T the sand is all in the bottom section. If the original and the final weight of the hourglass with sand is W, what is the force (or weight) read by the scale during the time in terval from t=0 to t=T.


REFERENCES: (PIRA 1G30.30) See the Demonstration Reference File for a large collection of reference materials.

EQUIPMENT: "Hourglass" with sand on damped scale, as photographed.

SETUP TIME: 5 min.

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