What Happens to a Candle and Mercury in a Freefalling Elevator?

[Julian Solos]

"There is a lit candle in an elevator mounted on a bracket attached to the middle of one wall (say, 2" from the wall). A drop of mercury
is on the floor. The cable snaps and the elevator falls.
What happens to the candle and the mercury?"

From: http://research.microsoft.com/~mbj/Smiley/Joke_Thread.html


Maybe the question was meant to be a joke, but it doesn't have to be.

 

[Njorl]

The blob of mercury becomes more spherical, as surface tension no longer contends with much gravity to shape it. Since the elevator descends with acceleration due to g-air resistance, and the mercury has negligible air resistance, there is still a little pressure deforming it.

I assume the candle is lit, otherwise the question is dull. Candles depend on hot gases rising to feed the flame. In this case, the candle is nearly experiencing freef-fall, so there is little gravity to cause the hot vapor to rise in relation to the cool air. I suspect it would still burn, but not nearly as well. Just a little preferential directionality can cause a strong fluidic flow. If you've ever done the experiment with a candle burning at the bottom of a long glass tube, you know what I mean.

Njorl

 

[Gara]

but the air would be falling at the same rate as the cadle, so i think the cadle would have no change.

 

[Njorl]

Originally posted by Gara
but the air would be falling at the same rate as the cadle, so i think the cadle would have no change.

The air and the candle would both be in freefall. There would be no reason for hot vapors to rise. If the vapors don't rise, the candle goes out. As noted though, the elevator won't quite be in freefall, so the candle might stay lit. This is assuming a hermetically sealed elevator though.

Njorl