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Demos: 1E-03 Candle in Rotating Bell Jar


A lighted candle is placed under a bell jar (the jar’s purpose is prevent any drafts on the candle), the jar is anchored to the edge of a turntable and the turntable set into rotation. Surprisingly, the candle flame tilts toward the center of the circle, illustrating how in the frame of reference of the candle, local up is not the same as when it is stationary. A candle flame burns “upward” because the lighter gases move along the pressure gradient in the jar. This gradient is in the direction of local “up,” defined to be the vector resultant of the actual acceleration, a, and the vector - g. Directions: Place the candle in the holder, light the candle and quickly place the bell jar over the candle. The bell jar fits in a “V” groove so that it will not slide off the table. Spin the table fast and the candle will be easily observed to tip toward the center of the circular path.

Suggestions for Presentation: First place an object, such as a pen or book matches on the turntable and ask what will happen when the table is rotated. Students will correctly guess that it will slide off. Then ask what will happen to a candle flame. Will it be “slung” toward the outside, too?

Applications: Cite numerous cases where what you observe in your (accelerated) reference frame seems to contradict Newton’s Laws.

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Last Updated: May 9, 2016 11:44 AM

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