A student cut out a spiral shape from a piece of tissue paper and hung it from a string over a light bulb. Nothing happened. Next the student turned on the light. After a few seconds, the spiral began to turn above the light. Which of these best explains what happened?

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Explanation:

Initially, when the paper is hung over the light bulb, we observe that nothing happens at all.

As time goes on, air surrounding the lamp begins to heat up. Remember that hot air is lighter and less dense than cold air.  Air surrounding the lamp which has now become hotter and less dense rises and pushes on the spiral. This causes the spiral to begin to spin.