You know it's possible to use ice to start a fire.
Here's a story of water starting a fire.
UPDATE 1: This space reserved for the first commenter with video showing that they used a bowl of water as a lens to start a fire. Get out there, Mythbusters! I will link to your video clip!
UPDATE 2: Our attempts with a large, hemispherical mixing bowl and black posterboard lead me to doubt the likelihood of this explanation. The dog bowl in the story is a frustrum of a right circular cone, so lensing effects don't seem plausible. One might retreat to a position that the rim of the bowl acted as a mirror. But reflections from a water-glass boundary? The intensity simply isn't there.
In my Mythbusting opinion, the "dog bowl as magnifying glass" explanation holds no water.
6 comments:
Sad but awesome.
Reminds me of Golding's description of how Piggy's glasses were used to start a fire in The Lord of the Flies. Piggy was nearsighted (as I recall) and thus would need a DIVERGING lens. Maybe he meant to say they started a virtual fire?
If the water bowl in question was hemispherical, then I believe the rays from the sun would diverge upon leaving the water-bowl interface.
I think that if a bowl was the cause of that fire, it was due to somebody doing a bowl near the dog's water dish.
I've ben able to use a hemispherical mixing bowl to "smoke" some black posterboard and dry leaves. Actual ignition was not observed.
The dog bowl doesn't seem to me to have any particular "optical qualities."
If I cut some glass into a disc, that doesn't make it a lens. The water-filled dog bowl is little more than a disc of refracting material.
But I eagerly await a nice confirmation video.
I know the person whose house was burned and last week we watched as the fire dept recreated the fire. the bowl was hemispherical.
http://seattletimes.nwsource.com/html/localnews/2009253757_firebowl23m.html
@Anon, I'm limited by my access to evidence. But
1. The dog bowl shown in the news piece was flat.
2. The wire rack shown in the piece has a flat "bed" on it. It appears it would support the bowl shown in the piece securely, but a hemispherical bowl would seem to tilt and shift.
A video of the fire department's recreation of the fire would be a valuable teaching tool. I promise to make a new post devoted to it should I ever get access to it. Please send a link.
The configuration shown in Keenan's reenactment would not work as a dog's water bowl. That bowl would be in pieces on the deck after three laps.
Don't get me wrong: I'm rooting for the object optics lesson--I'm a physics teacher! But I did have difficulty reproducing it with bright sunlight and black posterboard.
Dean, the Seattle Times article cited by Anon shows the fire department using a curved bowl to test their hypothesis. The TV new report says "a dog dish like this." I suspect the TV crew grabbed the nearest glass bowl and used it as an example. I put my faith in the firefighters using a bowl that matched the bowl found at the scene. I vote that it's possible.
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