Thursday, July 05, 2007

How High are the Iowa City Fireworks?

If you saw the firework in Iowa City you know I had some time on my hands. It seems the city planners decides to stretch out the show bit by resting 5 to 10 minutes after each volley. I guess someone kept dropping the match. So using a few physics, astronomy and math I came up with some cool numbers. The two key numbers were based on two facts. The speed of sound in warm air is about 1145 feet per sec. Using my digital watch the time between the "flash" of the firework and the "bang" of the explosion was about 1.25 seconds. The second piece of information is your fist held at arm length subtends about 10 degrees. That mean the fireworks were about 40 degrees off the horizon.

After doing the math here are the result. The height for the fireworks was about 880 feet. this goes nicely with a NOVA special I saw on fireworks. The average diameter of the display was 480 feet. Another number that fits nicely with know data. The muzzle velocity of the shell is at least 162 mph. Most Firework shells are round and fired like a mortar round, so there is air resistance. This number is probably low.

Wanna check my work?

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