Baby, you're a firework!

Happy new year guys! For today's post, I thought I would dedicate it to fireworks! Luckily, I was able to see some last night but I know many of us did not get to watch fireworks this year, so why not read and learn more about them instead? Haha anyway, before I begin I just want to wish you all an amazing year ahead. I know 2020 was not what we all had in mind a year ago from today but it has only made us stronger and more prepared for what's to come. Enough with the sappy stuff, let's get learning! Lol, count the number of times I say "let's" in each blog post 😆. (Don't actually count it though because you'll probably be sitting here for hours.)

What are fireworks?

Simply put, fireworks are small explosives or "rockets". They are made to perform controlled explosions to display colours and light for entertainment purposes. There are many types of fireworks but we will focus on aerial fireworks which are the ones that are fired into the sky.

Figure 1: Annotated diagram of an aerial shell.

The aerial shell in Figure 1 is the source of the explosive chemicals that give rise to different properties of fireworks. Both the gunpowder and stars depicted in the image are explosives. The bursting charge of the aerial shell contains a fuse with is lit up and thus triggers the bursting charge to explode, spreading the flame or spark to the rest of the aerial shell. The stars are what we actually observe when watching fireworks. They source the colour and patterns. When the stars react with heat, the oxidizing agent and fuel that are inside them, undergo chemical reactions that result in the formation of heat and gas.

How do fireworks work?

Okay, I know what you're thinking. That sounds awfully fast, how do the aerial shells manage not to explode midway? We're only just getting started! A firework explosion has two steps: the aerial shell is shot up and then it explodes in the sky.

The aerial shell is first put into a mortar which is essentially just a tube. If you've ever tried to do fireworks, you probably know that fireworks are usually buried in sand or dirt. Below the aerial shell, there is a bit of gunpowder attached to a fuse. When the flame or spark reaches the gunpowder, it explodes creating an ample amount of heat and gas which in turn creates an increase in pressure that will allow the shell to be propelled into the sky.

In a matter of seconds, the shell will be higher, and the time-delay fuse inside the aerial shell will set-off, leading to the explosion of the bursting charge. The production of heat and gas by the gunpowder and stars inside the shell will cause the shell to open and thus, the light of the fireworks to burst into the sky. The way that the stars are arranged in the aerial shell will determine the patterns that we observe.

The Chemistry

If you recall Charles' Law, the increase in the temperature of enclosed gases is proportional to the increase in volume, given constant pressure. As I mentioned before, a lot of the reactions taking place produce a ton of heat and gas. Resultantly, the increased temperatures, cause the gases in these firework explosions to expand. This expansion of the gases actually leads to the loud sounds we hear when watching fireworks. You may have noticed that often we can see the fireworks before we can hear them. It turns out that the gases expand faster than the speed of sound, explaining why the "boom"s are heard at a slight delay.

The different colours of fireworks you see are made possible by the metal-containing colourants in the stars of the aerial shells. If any of you are science kids, you may have done experiments in the lab where you burn different metals and as a result, you observe different colours. This is the same idea. The electrons in the metal atoms absorb heat energy which allows them to become excited and thus jump to a high energy level. However, they then go back down to a lower energy level, the previously absorbed heat energy is released as light energy.

Figure 2: Picture depicting which metal compounds give rise to which colours.

The Physics

Like everything else, fireworks obey the law of conservation of energy which outlines that energy is neither created nor destroyed but just converted between its forms. Thus, the chemical energy of the fireworks stored in the aerial shells and mortar is converted into the light, heat, sound and kinetic energies that we observe.

The upward shooting nature of fireworks also follows Newton's third law of motion, stating that every action force has an equal and opposite reaction force. The heat and gas emitted by the burning of the gunpowder move backwards toward the ground, allowing the "rocket" to fire in the opposite direction (toward the sky).

Safety

As cool as they are, I think it's safe to say that they are super dangerous as well. No pun intended... unless you laughed. Various guidelines must be followed in regards to the proper use of fireworks. If you are of legal age to buy and do fireworks, please be careful and make sure you are following all of the rules to ensure everyone's safety.

That's it for me today. Have a great rest of the day and year everyone!

Citations

Antonis, K. D. (2010). Fireworks! Retrieved January 01, 2021, from American Chemical Society
Conners, D., & Anderson, P. S. (2020, July 4). How do fireworks get their colors? Retrieved January 01, 2021, from https://earthsky.org/human-world/how-do-fireworks-get-their-vibrant-colors
Woodford, C. (2020, April 13). How fireworks work: Firework science. Retrieved January 01, 2021, from https://www.explainthatstuff.com/howfireworkswork.html

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