Simple facts behind the fireworks~

  7월 28일 부터 8월 4일까지 포항국제불빛축제(Pohang International Fireworks Exhibition)가 있다고 하죠~
  그런데.. Do you know what makes fireworks WORK?
 
  한번 생각해 보신 적 있는지요-
  다 아는 이야기일지도 모르지만, 혹시나 궁금한 사람들을 위해 몇가지 소개합니다~^^
 

 짙은 밤하늘을 배경으로 화려한 불꽃들을 장식하는 순간의 스펙타클 쇼를 위해--
 Pyrotechnician들은 미리 구상한 계획에 필요한 계산을 합니다

 물리학이라고 하기는 너무 거창하고-, 여러 가지 크기의 불꽃을 어느 위치에서 연출할 것인지를 결정하는데 적용되는 간단한 원리를 소개하겠습니다.

 추진 화약(금속이온, 산화제, 환원제 등의 혼합물)을 정해진 지름과 높이가 있는 Shell(원통)에 넣고, 일정한 각도로 조준하여 불을 붙이게 됩니다.

 이 때,
 "사용되는 원통(shell)크기와 화약의 양에 따라 초기속도(initial velocity)를 조정하는데,
  화약이 든 원통은 중력의 영향을 받으면서 수직 상승하고,
  조준한 각도가 있으므로 수평 이동을 동시에 하게 되므로,
  최종적으로 불꽃이 터지는 위치는 점화시켜 출발하는 순간의 수직상승속도(초기속도)와 출발 후 하  늘에 채류하는 시간을 알 때, 피타고라스정리, 삼각함수의 간단한 공식으로 구합니다"

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 Shell의 지름이 다른 종류 여러 개(2inch ~ 12inch)를 같은 각도(75 degree)로 쏘았을 때를 예를 보면.. 한눈에 들어오네요^^

 
 물론, 불꽃의 위치 뿐 아니라 모양과 터지는 시간 등도 고려를 하게 되는데, Shell 내에 화약(Black powder/Gun powder)와 함께 Time-delay fuse가 있어 최종 불꽃이 터지는 시간을 조정한다고 합니다.
 
[#M_International Visitors Click -|Close.|Reference source > http://library.thinkquest.org/15384/physics/index.htm
 
 Most people don't realize the vast world of physics that takes place during every fireworks show. The science of pyrotechnics involves many physics applications that must be considered to produce entertaining displays. Pyrotechnicicans must take into account the relationships between vectors, velocities, projectiles and their trajectories, the explosion forces behind burst patterns, etc.

The relationships between the initial velocities and the distances traveled by the shells can be understood and manipulated by using the following formulas and mathematical methods:

Y=VyT+0.5GT^2

Y=vertical height, Vy=initial vertical velocity, T=hang time, G=acceleration due to gravity

X=VxT

X=horizontal distance, Vx=initial horizontal velocity, T=hang time

The Pythagorean Theorem - a^2 + b^2 = c^2

a or b = vertical or horizontal velocity, c=resultant initial velocity

The Trigonometric Functions - sine, cosine, and tangent

In a right triangle sine=opposite side/hypotenuse, cosine=adjacent side/hypotenuse, tangent=opposite side/adjacent side

2"- 12" Shell Trajectories Fired at 75 Degrees

The first two formulas you see are primarily used to chart trajectories like in the graph on the left that shows the flight paths of 2" through 12" shells fired at 75 degrees. These graphs are very useful tools that allow pyrotechnicians to visualize how high and how far their shells will travel during a show. This information can be used to aid the process of choreographing the show to music, and determining if some shells will exceed the safe zone for that particular site. The Pythagorean Theorem is used to find a certain initial velocity value if the other two are known. This is helpful in determining information needed for the other formulas. The Trigonometric Functions are also used to find initial velocity values, but are used to find vertical heights, horizontal distances, and firing angles as well. Pyrotechnicians use these mathematical methods along with charts, graphs, and computer programs derived from them to plan their impressive displays.

 Pyrotechnicians must also consider shell burst sizes when planning shows. They must know how big certain bursts are when compared to others so that the choreographing of the show is in sync and so they don't exceed their safe zone requirements. As with initial mortar velocities, the bigger the shell size the larger the effect. It follows the same principle in that larger shells contain greater amounts of chemicals that when ignited produce greater explosion forces than do smaller shells. This results in varied burst sizes. Shell burst sizes are usually about 45 feet in diameter for every inch in shell size, depending on how tightly the shell is packed. As you can see in the diagram on the right, the differences in burst sizes can be extremely huge. It is just one more thing that pyrotechnicians must take into account to produce entertaining and attractive fireworks shows.

 Pyrotechnicians must master many different types of science in order to create attractive displays.

Reference source > http://library.thinkquest.org/15384/physics/index.htm

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