Friday has arrived, and right on time for the weekly "A Taste of Physics" column — episode 29.
This week: combustion processes, photons of light, and the engineering marvel hidden inside fireworks.
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The video shows the combustion of titanium hydride — a compound of titanium and hydrogen.
Its bright sparks and slow burning process have made it a key ingredient in the fireworks industry.
How do fireworks work?
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A candle and a ballistic missile are both examples of combustion.
The main difference between them is the rate at which energy is converted into light and heat. A candle burns slowly; a ballistic missile burns rapidly and explodes.
Designing fireworks involves the launch and directional stability of the shell, the shape it forms upon explosion, the colors it emits, and its precise timing.
The launch is carried out by a standard explosive charge and a short tail fin to maintain directional stability in the air.
The shape is determined by dividing the firework into compartments of different geometries, so that each compartment explodes in a predefined pattern and direction.
Timing is controlled by various delay mechanisms.
The simplest are insulating partitions between compartments and delay fuses of the required length.
In more expensive fireworks, one can find electrical circuits and electronic chips that allow the explosion to be timed and even synchronized with music or other fireworks.
The colors of a firework depend on its chemical composition.
Metal salts are typically used, because they begin to burn at a suitable temperature — neither exploding too quickly nor burning too slowly.
An added advantage is that these materials convert combustion energy primarily into light, rather than heat and shockwave.
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The different colors these materials emit depend on the orbital paths of their electrons.
When an atom absorbs energy, its surrounding electrons jump to an orbit farther from the nucleus. The electrons then return to their original orbit, and in doing so release photons of light.
The greater the distance between the orbits, the more energy is released and the more the light shifts toward the blue end of the spectrum. When the distance is smaller, the energy is lower and the light shifts toward red.
Shabbat Shalom 😊
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