Table of Mechanics Demonstration

List of Mechanics Equipment & Supplies

Lecture Demonstrations

Pail of Water, 1D50.40

Topic and Concept:

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A partially filled pail of water is whirled around in a vertical circle without spilling any water, illustrating centripetal force in conjunction with Newton's first and second laws.



ID Number


ME, Bay A9, Shelf #2


Important Setup Notes:

Setup and Procedure:

  1. Partially fill the bucket with water.
  2. Start with the bucket about an eighth of a turn in the direction opposite to the rotation.
  3. Swing the bucket in a vertically-oriented circle with enough speed so that all the water remains in the bucket.

Cautions, Warnings, or Safety Concerns:

Discussion: According to Newton's first law, objects in motion tend to continue moving at constant velocity in a straight line unless acted upon by a force. The water is always moving tangentially to the buckets trajectory due to a central force. Thus, this demo is also good for showing central or, more specifically, centripetal force. At the top of the trajectory, the force of gravity and the centripetal force are in the same direction. The water is falling due to gravity, but the bucket is falling faster. This is why there is a critical rotational speed that the bucket must attain. Newton's second law can be thrown into the discussion here. The total force on the water will always be the sum of the centripetal and gravitational forces.





fw: Pail_of_Water (last edited 2018-07-18 16:24:55 by srnarf)