Billy Rogers






The effects of sound upon the course of mankind, and indeed nearly all species, is phenomenal. Without sound, one would not be able to facilitate the ability to hear, and thusly would not be able to notice the presence of noise, due to the absence of sound. However, I first feel that it is necessary to define several of the terms that I will be using within my research paper, so as to create a clearer understanding of the concept that I am addressing. Sound is easily defined as "created when something vibrates setting up small fluctuations in air pressure" (Alcock). Other important terms in my paper are, according to Random House Webster's College Dictionary, Pyrolysis: The subjection of organic compounds to very high temperatures. Oscillate: To vary between maximum and minimum values, as of a cycle or mathematical function. Frequency: The number of periods or regularly occurring events of any given kind in a unit of time, usually one second. Amplitude: The absolute value of the maximum displacement from a zero value during one period of an oscillation. And Acoustics: The branch of physics that deals with sound and sound waves. 


The purpose of this investigation is to discover the qualitative relationship between amplitude and frequency (herein referred to as acoustics), and their effects upon a single flame, if any.


"Sound appears to be a topic distinct from motion and heat. However, we now understand sound to be an ordered motion of the molecules of the medium through which the sound propagates. The study of sound provides the opportunity to understand wave motion" (Sprott). I believe this to be very true, and backs me and gives me greater reason in my endeavor, as it is obvious from this that not only will I be analyzing the flame in and of itself and the effect that acoustics could potentially have upon it, but I will be able to monitor the sound and its vibrations, its frequency and its amplitude, all together while only the flame itself is the visual representation of all this. Furthermore, previous studies have already acknowledged the fact that acoustics do indeed have an effect upon flame, as proven in a study by Tae-Seong Roh, where he states, "Acoustic flow oscillations cause local changes in mixing and combustion processes in the gas phase… Subsequent variation of heat transfer to the condensed phase alters the surface pyrolysis and burning characteristics" (Roh). Essentially he is stating that acoustics will have an effect upon the characteristics of the flame, as is obvious when he mentions the change in the burning characteristics due to the change in the gas phase caused by acoustics. And finally, according to a study very similar in nature but with the aim of discovering the effects of sound on emissions from fire, Pinder discovered that "in the flow field oscillations, the flame structure was locally affected by the frequency of oscillation" (Pinder). Although this fails to directly give me an answer for what I am investigating, it does address the fact that the physical structure of the flame is indeed effected by the variations in acoustics, therefore proving to me that my time spent researching will be worthwhile. 


I believe that as the amplitude and frequency of the sound effecting the flame are altered, the flame will show the effects upon it. Furthermore, I believe that as the amplitude and frequency are increased or decreased, activity within the flame will either increase or decrease, respectively, showing a direct relationship between the amplitude and frequency and the flame. 


Roh, Tae-Seong. "Effects of Acoustic Oscillations on Flame Dynamics of Homogenous Propellants in Rocket Motors". American Institute of Aeronautics and Astronautics, Inc. 1995.

Alcock, Gillian. "Simple Acoustic Theory". 1998.

Nichols, Wendalyn. "Random House Webster's College Dictionary". Random House Reference and Information Publishing Group. 1999.

Sprott, Julien. "Physics Demonstrations". 1996.

Pinder, T. "Experimental and Computational Investigation of Dynamic Control Strategies for Non-premixed Flames". University of Michigan. 



1) Plumbing pipe 
2) Thin, hollow glass tubes
3) Drill and drill bits
4) Small speaker
5) Gas tube adapter, gas tube, gas source
6) Matches
7) Function generator
8) Sunglasses (safety may be first, but style is so much better)


To begin, I constructed the device that I will refer to as the flamethrower. I made it out of a plumbing pipe, hollow with holes at each end. At one end I put a cap on it, and at the other end I taped the speaker onto it. On one side of the tube, I drilled three holes, in a line, each pretty close to the other, and all of varying sizes. Into these holes I inserted 10 cm pieces of the hollow glass tubes, each of a slightly different size, and superheated in order to seal the hole and become stable once they were inserted. On a side 90 degrees from the side where I placed the three holes, I placed the gas adapter, using a similar method of drilling a hole and placing the adapter in it; however, I used tape instead of superheating the gas adapter because I was wary of warping the structure of the adapter. Following that, I taped every object not originally part of the plumbing pipe to the frame of the pipe in order to stabilize everything, using electrical tape. 

As for the experiment itself, it is really quite simple. I merely attached the hose that provides the gas for the flamethrower to the gas adapter, and the other end of the hose was attached to the gas supply. At the flick of a switch gas was pouring into the flamethrower and out of the three small tubes attached at the top. Then all that was needed was to light a match and hold it above the gas exiting the three tubes, and voila! Fire. Then to apply sound to the flamethrower, all that was left to do was attach the black and red wires on the function generator to the black and red (in that order) wires attached to the speaker that was taped onto one end. Then press the PWR button on the function generator, it's the red one. Then you just play around with all the dials and stuff until stuff starts happening to the flames coming out of the three tubes. 





High Frequency, Low Amplitude 
Characteristics of Flame: Shorter, fatter flame, seems almost lethargic


High Frequency, High Amplitude 
Characteristics of Flame: Longer, taller flame, more energetic


Low Frequency: At lower frequencies the flame exhibited behavior akin to that of flickering. It flickered. The higher the frequency, the less the flickering was present in the flame. However, as the frequency diminished, and the time period between approaching sound waves increased, the flame began to flicker. As the frequency continued to drop, the flickering would become slower with longer and longer time periods between the presence of the flame. Eventually, if the frequency dropped low enough, the flame would go out altogether, due to the longer time periods between which it would be lit. 


There is, unfortunately, a very high level of uncertainty present in this experiment. Some of it is a merely a result of a lack of foresight, while others were unavoidable. There is, of course, the traditional human error effect, but that was fairly minimal in a qualitative experiment such as this. Rather, the primary problems stemmed from a lack of understanding of the function generator, the effect of the wind on the flame, and the placement of the holes on the tube. 

First of, the function generator was (still is) a very confusing device. It has a lot of buttons. Some of those buttons even pull out. Which is unfortunate because I know that that does something, but I couldn't figure it out. Similarly, only three knobs controlled the frequency and amplitude, whereas there were three other knobs that somehow affected things, and there were also buttons which changed the shape of the wave exiting the generator (I think) and which changed the amount of megahertz that I was operating in. I kept the three unknown knobs, wave changer, and megahertz changing stuff all constant in order to isolate the effect of the frequency and amplitude on the flame, but I am fairly certain that they had some sort of an effect on the experiment. 

The wind problem is pretty self-explanatory; wind was blowing the flame as I tried to watch it. I mean, I couldn't even breathe when I was looking at the flame. Then somebody would walk by and the flame would go psycho. I gathered what I could however, but the wind greatly influenced the behavior of the flame, and therefore messed with my pictures and results. 

Finally, the placement of the holes on the tube most likely effected the flame as well. Considering that the hole could be picking up the sound wave at a certain point (ie crest or trough) and that it could also be picking up the rebounds of the sound waves, the placement of the holes had to of had an effect on the flame. Fortunately, I don't believe that it had a very large effect, simply because by keeping most everything constant, then I was mainly able to analyze frequency and amplitude, but again, I'm fairly certain that this factor had some sort of an effect on the behavior of the flame. 



I believe that this experiment validated my hypothesis. The flame did, in my opinion, display behavior that reflected the changes in the frequency and the amplitude. As I would decrease the frequency, the flame began to flicker and would eventually go out. As I decreased the amplitude, the flame became shorter and fatter. These two factors prove that there is a direct relationship between sound administered to a fuel supply and the behavior of a flame fueled by that supply. 


To begin, I would make a point of learning about the function generator before embarking on this experiment ever again. Additionally, I would place the flamethrower mark II in a sealed container, preventing the effect of wind upon the behavior of the flame. Finally, I would make a whole new flamethrower, which was alluded to in the previous sentence, with the concept of the whole "mark II" idea. Ideally, this new flamethrower would be perfectly airtight, allowing no gas or sound to escape. Also, it would take into account the effect of the placement of the holes and the placements effect on the experiment. To be frank, I have no idea how this would be done, but it would be nice if this was taken into account and analyzed and a solution to that little problem was found. Other than that, I quite enjoyed walking into period 2A physics I class, and terrorizing them with my food, strange dress, loud noises, smelly gas, and flames. Sometimes I would just let that bad boy burn. I loved it. But anyways, I'm getting off track here… other than the aforementioned things, I am not entirely sure what else I would be able to change. Maybe the size of the holes drilled into the tube also would create an interesting effect on the experiment. But I certainly believe that the largest problem, and thing that would need to be fixed the most, was a general lack of knowledge about the function generator. Also, it would've been nice if we had been able to hook up some subs to that little flame tube and let her rock… anyways, a greater range of flexibility as far as the materials used to experiment would have been nice as well, but I was operating within a budget. It also would have been nice if I had not had surgery during the week that we chose partners and had not ended up doing this as a singular unit, but that is neither here nor there. Nor anywhere. Well actually I'm fairly certain it's somewhere, but I'm not quite sure where. To conclude, there are a plethora of things that could have been done differently, but that is much more easily discovered with the benefit of hindsight. I was jumping headfirst into something that I knew very little about, and at least managed to enjoy myself. That's all folks.



ADDITIONAL SOURCES: - This was Julien Clinton Scott's website, and was useful in assisting me to setup the           flamethrower itself. - This site discusses the nature and interaction of sound and flame. - This website discusses fire safety, and is probably a good idea to review if you ever plan on making a flamethrower and then using it inside the school. - This website is a table of contents for multiple pages on sound, the nature of sound, and a number of other sound related things.