Here's a Question! - Why Does the Water Rise?
When a lit candle that's placed in a shallow tray of water is covered with a beaker, the candle goes out and the water in the beaker goes up. What happens when three candles are used?
Announcer: Frostbite Theater presents... Cold Cuts! No baloney!
Joanna and Steve: Just science!
Joanna: Hi! I'm Joanna!
Steve: And I'm Steve!
Joanna: Here's a question for you...
Steve: When a lit candle that's placed in a shallow tray of water is covered with a beaker, the candle goes out and the water in the beaker goes up.
Joanna: What happens when three candles are used?
Steve: Do both sets of candles burn for the same amount of time and the water level in both beakers rise by the same amount?
Joanna: Does the single candle burn longer and the water level in both beakers rise by the same amount?
Steve: Does the group of three candles burn for longer and the water level in both beakers rise by the same amount?
Joanna: Or, does the single candle burn longer and the water level of the second beaker rise by a greater amount?
Pause the video now if you'd like to think it over before we show you what happens.
Joanna: First, let's talk about the candles. They consume oxygen as they're burning, and there's only so much of it in the beakers. Eventually, there isn't enough oxygen in the beakers to keep the candles burning, so they go out.
Steve: The more fire there is, the faster the oxygen gets used. That's why the group of three candles goes out before the single one does.
Joanna: Now, for the water. The pressure in the beaker drops, which is why the water is drawn into it.
Steve: A common reason given for this is that the fire's consuming oxygen. But, if that were the sole reason, then we would expect the water level in both beakers to be about the same. Because, whether it's one candle or three, about the same amount of oxygen is being used.
Joanna: There's actually a lot of things going on.
Steve: Oxygen is being consumed.
Joanna: Carbon dioxide and water vapor are being produced.
Steve: Water vapor is condensing onto the walls of the beaker.
Joanna: We think the biggest factor is that the beaker is trapping hot air from the candles as it's being lowered into position.
Steve: You get more hot air with three candles than one, so you get a greater effect with three candles as that hot air cools back down to room temperature. But, we'll leave it up to the viewer to experiment with this further. Maybe as a science fair project or something.
Joanna: Thanks for watching. We hope you'll join us again soon for another question!
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