Saturday, July 15, 2006

Insulting Stupid Movie Physics

Insulting Stupid Movie Physics is such a great website.

I particularly enjoyed the article on the classic movie cliché: cigarettes lighting gasoline.

"The explosive or flammable range for gasoline is about 1.4 to 7.6% gasoline vapor in air. Outside of these limits, gasoline cannot be ignited. A large amount of gasoline in an enclosed can usually will not form an ignitable mixture since the vapor concentration will be too high.

We lit a cigarette and tossed it into the pan. The cigarette paper wicked up gasoline and quenched the glowing tip without igniting anything (see Figure 4). We tossed in more lit cigarettes. We tried lighting gasoline soaked paper towels. We used long tongs for reaching far away objects to hold glowing cigarettes over the pan at various heights. More than once we placed several glowing cigarettes in the pan (see Figure 5). Our record was 40 glowing cigarettes at one time. In most cases, we allowed the glowing cigarettes to smolder until they went out.

Various experiments were conducted at different times of the day with different air temperatures and humidity
. A total of 223 cigarettes of 11 different types were eventually used all without ever igniting the gasoline. Yet, at the end of each experimental session the gasoline was successfully lit using a single match attached to a long pole (see figures 6 and 7). The gasoline would typically ignite just before the match touched it. This indicated that there was an ignitable mixture just above the surface of the gasoline. Numerous lit cigarettes were in this region for significant periods of time."

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