In the book Albert Einstein- Historical and Cultural Perspectives- Banesh Hoffman states: I now want to tell about a small dinner party that i was invited to at the house (Einstein’s) on Mercer Street in Princeton. While tea was being served from a teapot and not via tea bags – Einstein pointed out that when one stirred one’s tea, the tea leaves congregated at the middle of the bottom of the tea cup and not at the perimeter, where one might expect them to congregate. He asked me if i knew why?
Einstein asked: Imagine a lighted candle in an enclosed elevator. The cable breaks and the elevator falls freely. What happens to the flame of the candle? Since the answer depended on Einstein’s famous principle of equivalence, i was able to figure out what would happen> with zero gravity in the falling elevator, hot gases would not rise, and the candle flame would therefore be snuffed out.
Albert Einstein- Historical and Cultural Perspectives, Mineola, NY 2012 reprint