Teenage Physics

Teenage Physics

or... The Fascination With Sudden Combustion

None of the names have been changed in order to protect the guilty... or the innocent, either, for that matter.

One fine spring weekend afternoon, my best High School friend and I achieved amateur-hour potato-cannon nirvana. It was about two years... or was it three?... after my first and only "hunting trophy" was taken with a bristled weapon...

? huh? "bristled weapon" you say? What the heck is... Ok, I suppose I need to digress and explain that episode first, before we get into the potato cannon part.

You see, I was an only child, and a rather lazy only child at that (but at least I'm honest about it). So, late one Saturday morning in the not-quite-yet fall, September of 1976 or '77 if I recall correctly (shortly before the leaves really began to fall in earnest, at least it was), my dad, seeing me not busy enough with sufficiently important things in his judgement, ordered me to grab the push-broom and sweep the driveway. Of course, I eagerly jumped up and shouted "Oh Boy!? You mean I get to do some work!!??" Well... no. I'm sure we all know THAT was a great big lie. Nope... I resisted the command from my Lord of the Manor House. I whined... I complained... I even threw in a healthy serving of dithering... but in the end, I very reluctantly acquiesced to the withering glare from my sire... slooowwly got my jacket on (alas, no reprieve from this opressively arduous sentence was awarded by Mom, despite my giving her ample opportunity to speak up)... and so I eventually went downstairs to the basement and out through the garage and grabbed the big wide-headed push-broom (there being no sane reason to take the narrower push broom and have to do even more work than necessary, after all), and sauntered slowly out of the garage door and despondently began the arduous Labor of Hercules of sweeping the gravel, leaves, and other normal detritus and debris deposited by the swirling winds in our driveway down and out to the street.

I had to ever so slowly and reluctantly work the big, wide broom head around Dad's car and Mom's even bigger chevy sedan... a massive supercarrier of a vehicle if ever there was one! (In later years, when I was tasked to drive her car for whatever reason, I did so nervously, wishing for some additional crew members to be stationed as lookouts at the 4 corners of her ginormous-seeming 1974 Chevy Caprice Classic to assist me in having enough clearance to drive this great big beastly boat of a vehicle safely enough. I joked to myself about needing to "turn it into the wind" to receive landing fighters and strike aircraft atop its vast expanse of hood and trunk).

Since I was using the wider and more unwieldly BIG broom around the smaller driveway border confines of her enormous car, it was actually MORE work... *sigh* so what was a lazy pre-teen to do, but take multiple, progressively longer breaks... further delaying the completion of the fatherly-appointed Herculean Task of the day.

Due to my well-practiced and extremely-highly-ranked competitive sloth-y-ness skills, I was both brilliant and exceedingly successful at delaying the completion of the job at hand... all the way to the point that while it LOOKED like I'd swept the driveway (mostly), I hadn't completely finished it - really. It grew late enough that the approaching dinner hour and fading daylight - soon followed by dusk, that I not-so-carefully set the broom aside (erm.. I actually meant "cleverly, skillfully, and with much guile-of-the-skillful hunter precisely placed it") by propping it against the (hardly ever used) left-side garage door in front of my mom's car, in a somewhat semi-concealed spot that was partially shielded from the swirling driveway winds by both being propped up against the garage door and by mom's nearby Very Large People-(/"Aircraft-") Carrier car. So, I sauntered - self-congratulatingly at my eventually successful slothfulness (yeah yeah, I know... not good) - inside for dinner the inadvertent, er, uhm, "carefully arranged"... hunting trap having now been skillfully set.

After dinner, the by-now-forgotten broom... stayed right where it was, despite any efforts by the nocturnal breezes to disturb its rest. After dinner, TV time came and went, bedtime arrived, and soon, morning was upon us. As I scurried off to school, I saw the broom, but was about to run late, so ignored it. Dad may or may not have seen it (if he did, which is in retrospect rather likely, he must have decided to lambaste me for it later that evening and he too left it where it was) as he hurried off to work several minutes after me too. Later, in the early afternoon when mom had to head off to her 2nd shift job at Western Electric, she absolutely had to have seen it and literally would have needed to step around it to get into her aircraft carri... uhm, car. But she too left my broom(/"clever hunting trap") undisturbed.

So now, you'd think that the next person to see it would have been me returning home first from school that afternoon. Well... apparently not. An adult male pheasant was apparently the next living being to have a close encounter with the casually propped-up broom... err, I mean, "cleverly devised and highly lethal booby trap". I'm purely guessing here - that after mom's car was no longer in position to partially protect/shield the broom from the influences of the swirling passing breezes that the geometry of our driveway was prone to generate, those swirling breezes must have been more successful at generating movement in the now relatively unshielded broom. Perhaps even to the point where it vibrated or even perhaps clicked against the wooden garage door as the breezes jostled it in place. Whatever the case, the pheasant was attracted to approach this unusual object and/or noise for some reason. Nobody can say exactly what happened next. All that can be said with any certainty is that when I came walking up the driveway to get into the house in the afternoon, I was greeted by the sight of the broom having fallen over to the ground, and a few inches away from the farther end of the broomstick now laying on the ground was the male pheasant... quite dead, and with an indication in the distubed plumage atop its head, of having been struck by said clever and carefully planned booby trap... er, broom. I slowly approached the scene of my "kill", not sure of what I was seeing at first, carefully eyed the bird, looked at the broom, and actually said to myself, "Wow... I'm Good!" laughing at the result.

Yes. That's right, I'd apparently managed the exceedingly unlikely (and highly difficult, I assure you) task to hunt down and kill a pheasant... with our wide push broom's handle... while not even being there for the dénouement! (I take a bow to the undoubtedly enthusiastic congratulatory applause you're now granting me in appreciation for my... uh... creativity and avian hunting acumen.)

Anyway, some while later, when dad was due to return from work, I went back outside and was standing in the driveway, and stopped him from fully pulling into his accustomed parking area so he too could appreciate the amazing results of my hunt... er, ok, "the turn of events" and see the undisturbed scene of the crime... er, I mean the clever way I'd arranged for my successful "hunt".

Dad, who was doubtlessly prepared to admonish me for both leaving the full sweeping job undone and leaving the broom outside overnight was instead rendered speechless when looking upon the scene. He carefully observed the scene, and his eyes were drawn to the positioning of the objects as he took in the avian victim's corpus avis and the instrumentality of my hunting prowess' (ok, the broom's) resting place. Then, after absorbing everything, he went over to examine the pheasant, saw the disturbed plumage atop its head, and started laughing.

A moment later he picked up the bird by its feet, and declared cryptically "I know EXACTLY what I'm going to do with this!".

About a six weeks or so later, he amusedly presented us with my hunting trophy. He'd had the male pheasant stuffed and mounted on a partial section of a branch so it could stand freely, and that bird in the glory of its full fall plumage began its new career of collecting dust atop one of our bookcases as a silent testament to my "hunting prowess". He was so amused by the whole thing he never did yell at me (much) for not finishing the job of sweeping out the driveway... at least until the following weekend when he both made me redo the job, and also supervised me more closely to assure proper completion of the task.

In the next few months, Dad did make sure to invite the extended family over to our place so he could "show off my hunting trophy" (they all laughed at the story).

... Anyway, yeah, that was the story of the "bristled weapon" hunting trophy (a totally 100% True Story, too!).

So, yeah, back to what I was starting to relate... in the late spring of... it had to be '79? Right. Anyhow, my then best high school friend Ross (remember, my not changing the names to protect the guilty here, right?) and I'd been talking about a recent fad around the sophomore class-age teenage male community writ large..."potato cannons" and their many variations. He'd been doing a little "reading up" on the subject (so he said), and referred back to our recent-past's joint hobby of hunting up old beer cans lying around various places to add to our separate (and quite impressive, really) "beer can collections". (Yeah, we actually did that back then.) We'd had many the highly technical discussion over the minutiae about beer cans, their construction materials and construction styles (which changed in many ways over the years, it's really fascinating... but let us not digress here once again), having observed the flimsy newer-generation aluminum cans' alarming proclivity to attract dents and creases (thereby greatly reducing their value in a collection)

-vs- the prior state of the art steel beer cans... which were much less likely to accumulate similar damages - if one didn't count the rust, anyway.

Ross speculated to me that making such a potato cannon from the steel cans would make for a MUCH better and, of greater importance, much more powerful, potato cannon. I naturally inquired of him how we could construct such a device. He elaborated effusively, and I listened, much impressed with his theories and his acumen with the subject of constructing artillery in general. Y'see it involved perforating the walls between the tops and bottoms of the cans in a specific pattern designed to not impede the explosive force of the charge, and making sure the duct tape holding the cannon sections together would... uhm, yeah... It's probably for the best to not reveal too many trade secrets here, least this story be included in the annals of such compendiums as the Anarchists Cookbook or tomes of similar disrepute.

Anyhow, after several such conversations, Ross wanted to know when I wanted to try building one. I had to think about that for a few moments. We'd have to time it so that we'd be able to do it unobserved by any Parental Units, or they'd doubtlessly put a hasty stop to our experimenting with the fine art of crafting "dangerous artillery".

Several weeks later, the stars aligned, one Saturday. Mom was going out for several hours to get a new perm. Dad had some errands to run to get some parts for something-or-other he was doing or fixing, so he'd be gone too. To top off the fortuitous circumstances, I'd recently acquired, with root vegitable ballistics in mind, 2 empty steel tennis ball cans! I called Ross within my parent's hearing to ask him if he wanted to come over that late morning "to play" (wink, wink).

Ross, meanwhile, had managed to acquire some ballistic liquid fuel for our experimentation - a half-full rectangular quart can of Naphthalene (those of you readers who may be professional chemists may find that substance... alarming, and you'd be right, too as it carries about four times the energy release potential - in kJ/mol - of Acetylene, the gas they use for welding steel).

Around the time Dad was heading out, Ross came over. As Dad left, our ballistic experiments began with constructing the cannon. Ross was greatly pleased with the Tennis ball cans. We used both of them with a buffer pair of steel beer cans between them so we had five can tops and bottoms to strategically - and significantly - perforate (with an old triangularly-shaped beer-can punch opener - and other implements of precision destruction)... and enough duct tape to securely bind them into a nearly 2-1/2 foot long cannon. We added an ignition bore hole drilled into the bottom can's side about an inch or so above the can bottom, and Ross broke out his can of Naphthalene... and I supplied a few tennis balls (instead of irregularly-shaped potatoes - due to their more regular spherical shape, they should fly farther with less aerodynamic drag, y'see - plus, they fit into the open bore of the top-most tennis ball can with less margin for blow-by around the edges of the explosively expanding combustion products in the cannon. Or so we reasoned... (Ok, "wildly-assed guessed" - happy!?)

Finally, after about an hour of preparatory drilling, punching, inspecting, adjusting, taping, and re-adjusting... we were ready for our grand pyrotechnical and ballistic experiments to begin... once we... figured out the fueling and launching plans, that is. (Such procedures needed to be determine once the final geometries of the aligned parts was available for complete evaluation, y'see.)

Eventually, we took our finely crafted ballistic engineering creation giddily out to the now-empty expanse of our driveway, and Ross carefully poured out a measure of the Napthalene into the lid of the can, and then poured that reasonably small amount of the fuel into the base can of our cannon. I dropped in the tennis ball ammo like one would a mortar round, and we placed it vertically on the bottom can's flat bottom, and Ross lit it off with a cheap bic lighter he'd brought with him (I also had some wooden matches to use if needed).

And...*foof*!

It went off... the tennis ball did indeed launch out the barrel, but rather poorly, and with not so much energy... in fact it seemed to have sort of caught the lip of the top tennis ball can and get deflected off at a bit of an angle, also knocking over our cannon. The ball flew only a few yards over onto our front lawn, quite disappointingly.

Ross and I looked at each other, and basically said: "Harrumph. That was disappointing." nearly simultaneously.

We briefly evaluated the situation and considered what the remedy for this relatively poor performance might be. I ventured that we probably needed a bit more fuel, perhaps dropped down into the bore of the top can so it could trickle down the length of the construct, giving a greater surface area for the combustion. Ross considered this, mentally compared his prior reading against the larger volume of our bottom-stage tennis ball can against the more typically-used beer cans, and agreed, but also looked again at the mouth of our cannon's bore and speculated that the lip left from the tennis ball can's lid also played a role. While I agreed, we didn't really have the equipment (or the remaining parental-observation-free time) to remove that burr of the can lid rim. This frustrated us a bit, but we soon decided to soldier on despite the upper can lip problem.

Having reached a suitable agreement, Ross went with more fuel... pouring in an incrementally larger one and a half can-lids of the Naphthalene into the cannon, the half-lid went into the bore at the top, and the full lid of fuel into bottom can, and we reset the cannon and I dropped in the reused ammo tennis ball (which seemed no worse for the wear).

He again used his cheap bic lighter and we again touched off the improvised cannon.

*FOOM!* It went off!

Ross, however, reacted to 2 things. His hand hurt a little bit from a back-flash at the bore-hole, and the Biclighter's cheap aluminum top cover was blown off the lighter by the ignition flash, which also flew a short distance away from the ignition point.

This time the tennis ball definitely flew better - and much straighter, rising about 120-150 feet or so (clearly in our sight) above the driveway - and well above the roof line of my folks' 3 floor house (as measured from the garage, basement and driveway under the first floor to the attic crawlspace above the second floor), and safely bouncing down several feet away a few seconds later.

Ross and I were encouraged by this but still somewhat disappointed. Ross thought that with this heavy a thicker-than-beer-can-steel cannon base, it should have gone much farther. I concurred.

We took all those data points into account, and again revised our procedures, concluding that we both needed even more fuel, but also that putting our hands and fingers so close to the ignition point was probably not the best of ideas, either. I went with our long wooden fireplace-style matchsticks instead of his now damaged bic lighter, and I used a needle-nosed pliers to hold onto the base of the match stick once I lit it, keeping my hand a good foot or so farther away from the ignition point. We went with 2 full capfuls of the Naphthalene fuel, but Ross noted that "Oh, all the cans are kind of hot now, too". (This turned out to be highly important and relevant just a few moments later.)

We reset the cannon, reloaded the once-again safely reusable tennis ball ammo, and a few seconds later, I prepared to re-light the ignition. (This short delay, we figured later, proved crucial to what happened next as it gave more time for the Naphthalene fuel to warm up and mostly vaporize due to the many now-hot metal surfaces inside our cannon.)

I lit the match, put it into the pliers, and began extending it towards the ignition hole but well before I got the burning match head near enough to the bottom can's ignition hole...

*******KA- BOOOOMMMM!!!*******

We both went flying a few feet back onto our asses and then prone on the driveway from our previous positions a foot or two away but yet near the cannon. *BWEEEEEEEEEEEEEEEEEEE....* was the only sound in our newly blast-stunned ears...

A few seconds went by as I quickly performed a very distinct inventory of my body...(OK, fingers?... check. Toes... check. Ears? *BWEEEEEE*... note to self: trigger further diagnostics there later... hair?... yup, still there, check. Eyes/Glasses? Intact! vision working and glasses in place... Check. Clothes?... all there check. No blood leaking all over? Check! Initial integrity checks are good!). I began to survey the nearby environment as I dared to pick myself back up to a seated position. The pliers went flying from my hand and landed a few feet away from me, the formerly lit wood match abruptly extinguished by the sudden blast was several inches further away. I then looked over at Ross as he was obviously finishing up his own physical inventory of his body parts... coming to the same "two hands... check, feet still attached... check, clothes not on fire... hair NOT on fire... OK, no visible blood... check, clothes still on where I'd put them... check. OK... all good." conclusion that I had just arrived at for myself. He looked up at me as I was reaching up to my... EEEEEEEEEE!... ears while starting to work my lower jaw to see if that EEEEEEE! helped any with the concussion-induced sudden near-EEEEEEEEEEE!-deafness we were obviously both experiencing. As he looked at me, he began working his jaw similarly trying to further evaluate his own EEEEEEEEEEE... hearing.

We looked at our cannon a breath or two later. Or, perhaps I meant, what was left of our cannon... The bottom tennis ball can was literally shredded open like a blooming flower... blown apart from the inside by the force of the vapor detonation inside it (the petals of that "flower" all traced back to the former location of the burr hole in the wall of the can, we noticed later in post-mortem of the cannon), the rest of our cannon was lying in 2 pieces as both the lower and middle duct tape connections failed to hold it completely together after the force of the blast.

We both spent several very long-seeming seconds trying to regain the power of hearing anything beyond the concussion-induced EEEEEE ringing EEEEEE in our EEEEEEEars before trying to speak. A few more seconds went by, and I asked if he could hear me. He said "EEEEE a little, EEEE kinda EEEEE, but not well at all. EEEEEEE" We sat there flexing our jaws to try and restore some of our power to hear and taking in the scene of our destroyed cannon, beginning to think about what needed to happen next.

About 30 seconds or so after the detonation we were still trying to recover from the shock of it, when another shock arrived in the form of another sound - a NEW sound, but somewhat familiar. We'd never experienced one quite like this before though. You know that sound that tennis balls make on the tennis court after a strong serve, that hollow-ish bouncy sound? We both EEEEEE heard EEEEEE a MUCH louder version of that sound as the tennis ball bounced on the driveway a dozen or so feet from us with a much deeper and Louder hollow *Whunnnngggg!* sound announced the return of our projectile from its mostly-vertical flight. We both recognized the sound for what it was and we both swiftly rough-calculated how long the interval was between the detonation and the sound, and our eyes went wide. Then we both fell over laughing. We'd really done it! We'd really LAUNCHED that thing!

We laughed like loons for a good 15 minutes or more, "that had to be up for around 30 seconds or so!" feeding off each others mirth, laughing harder when I recovered the tennis ball after the 4th or 5th bounce or so (they were really high bounces, too - the first two taller than the 3 floors and roof peak's worth of height of my parents' house from the driveway). The tennis ball was DEFINITELY well-singed this time (but it did survive the launch and landing otherwise intact).

As we surveyed the wreckage of our cannon, we both quickly surmised that further experimentation with this mix of materials would be... ill-advised (and difficult to top, cannon-performance-wise). We speculated how high up it flew, having no really good way to measure it at all (it was around 1979 or so). We cleaned up the wreckage of our cannon (I buried the destroyed can down deep in the trash can to prevent parental inquiries), and we called it a very successful day... forgetting about the ongoing EEEEEEEE! blast-induced EEEEEEEE! hearing loss for each of us for the moment. We were too jubilant to care too much about it (and it was slowly getting better as more time passed).

Thus ended our youthful "potato cannon" experiments.

Ross and I (unlike our cannon) both survived and within a day or three could even hear normally again... We laughed some more about that later too.

------------

Recently, decades later now from the cannon's explosive finale, I was reminded of our ballistic experiments, and I asked the MS Copilot AI how high the ball would have flown vertically if it took around 30 seconds to land again. The AI figured that the ball soared upwards by around 3600 feet from our driveway (which sat at around 394 feet above sea level - Thanks, internet!). That put the launched ball into the space designated for the air traffic approach pattern for the mid-sized airport across town. I had to ask if the tennis ball could have shown up on the airport's radar back in those days. The CoPilot AI's answer, was "in theory, yes.... if they had a synthetic aperture radar system" (they doubtlessly didn't, so our tennis ball artillery round doubtlessly passed unnoticed by the airport radar folks - even if they were looking for it). Between the flight time of the tennis ball, and the altitude of planes on that approach pattern at that distance from the airfield, though, it - theoretically, at least - could have been a minor hazard to passing aircraft. (I can envision a pilot hearing the ball hit a wing or the fuselage under-surface and ask "what the heck just hit the plane!?") but the CoPilot AI concluded that the flight altitudes would have been relatively near the apex of its trajectory, so the ball would not have had enough kinetic energy left to present any significant hazard to any hypothetical aircraft it might, in theory, have struck. (*phew*!)

So yeah, it was both dangerous, and cool, and was neat to have done, but yeah... We never passed this story on to our kids, lest they be tempted to mimic our "success". Alas, (or "fortunately,") steel tennis ball cans are generally a thing of the past now too, and perhaps that's actually a Good Thing™ because with the energies of that detonation, there really was a serious risk for injury. We were very VERY lucky not to get seriously hurt.

But Damn... That was fun!