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Popping a balloon (physics geeks please read)
Tox
I kill threadsthey/themRegistered User regular
I kill threadsthey/themRegistered User regular
Sounds simple right? Wrong.
My Intro to Engineering class is working on a rube goldberg device. The device has to, as it's end result, pop a balloon. Said balloon must be filled with "air" and have dimensions no greater than 9 inches wide, 8 inches high, and a circumference less than or equal to 30 inches. No flames, no chemical reactions and, here's the kicker, no sharp objects. We're allowed to use one 9v battery, and one 1.5V DC motor, and the whole device cannot exceed a three foot cube "footprint." This included the post-popped balloon.
Although the professor seems somewhat confident that we'll be able to use something like a thumbtack, he's admitted he's not the final authority, and doesn't recommend we do so, so here's what we've got instead.
The final step of the device will be a pendulum. The pendulum will be on a ledge (probably higher than 90 degrees), and the previous step will knock the pendulum (lightly) over the edge, setting it into motion. The pendulum will swing down and knock a cardboard tube (from a paper towel roll) out from under a brick. The brick is supported by two such tubes, only one of which needs to be knocked away, and will be fastened to the balloon.
The way we're hoping to pop the balloon is to have the brick pull the balloon through a hole. The hole will be cut into a piece of plywood (or similar material) and will be lined with sandpaper. Our theory is that the weight of the brick pulling on the balloon will force the balloon through the hole, and the sandpaper will tear the rubber, thus popping the balloon.
Problem is, I haven't studied a drop of physics in about ten years, so...Questions:
1) What equation(s) can we use to determine how heavy a weight, and from what starting and striking angles, the pendulum needs in order to knock out the paper tube (this could easily be determined through trial and error, but an equation is preferable, to predetermine viability before proceeding to experimenting).
Solved! We're going to use trial and error, as majority believes that'll be the easiest approach, and we've got that kind of time.
2) How much "pulling" force is needed to actually pull the balloon down into the whole (again, equations welcome)[/s]
Solved! Again, trial and error. It probably won't take more than two bricks. If it does, we'll re-evaluate and redesign as needed.
3) Will this even work. Specifically, will a course enough sandpaper be functionally able to rip the balloon if enough force is applied? Can enough force be reasonably applied through gravity and a weight?
4) Is there a way to determine the optimal hole size (compared to a 30cm balloon circumfrence) that will make this idea function as intended.
My Intro to Engineering class is working on a rube goldberg device. The device has to, as it's end result, pop a balloon. Said balloon must be filled with "air" and have dimensions no greater than 9 inches wide, 8 inches high, and a circumference less than or equal to 30 inches. No flames, no chemical reactions and, here's the kicker, no sharp objects. We're allowed to use one 9v battery, and one 1.5V DC motor, and the whole device cannot exceed a three foot cube "footprint." This included the post-popped balloon.
Although the professor seems somewhat confident that we'll be able to use something like a thumbtack, he's admitted he's not the final authority, and doesn't recommend we do so, so here's what we've got instead.
The final step of the device will be a pendulum. The pendulum will be on a ledge (probably higher than 90 degrees), and the previous step will knock the pendulum (lightly) over the edge, setting it into motion. The pendulum will swing down and knock a cardboard tube (from a paper towel roll) out from under a brick. The brick is supported by two such tubes, only one of which needs to be knocked away, and will be fastened to the balloon.
The way we're hoping to pop the balloon is to have the brick pull the balloon through a hole. The hole will be cut into a piece of plywood (or similar material) and will be lined with sandpaper. Our theory is that the weight of the brick pulling on the balloon will force the balloon through the hole, and the sandpaper will tear the rubber, thus popping the balloon.
Problem is, I haven't studied a drop of physics in about ten years, so...Questions:
1) What equation(s) can we use to determine how heavy a weight, and from what starting and striking angles, the pendulum needs in order to knock out the paper tube (this could easily be determined through trial and error, but an equation is preferable, to predetermine viability before proceeding to experimenting).
Solved! We're going to use trial and error, as majority believes that'll be the easiest approach, and we've got that kind of time.
2) How much "pulling" force is needed to actually pull the balloon down into the whole (again, equations welcome)[/s]
Solved! Again, trial and error. It probably won't take more than two bricks. If it does, we'll re-evaluate and redesign as needed.
3) Will this even work. Specifically, will a course enough sandpaper be functionally able to rip the balloon if enough force is applied? Can enough force be reasonably applied through gravity and a weight?
4) Is there a way to determine the optimal hole size (compared to a 30cm balloon circumfrence) that will make this idea function as intended.
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If the hole size is too small the balloon will simply absorb the blow from falling and sit atop the hole. You want the whole to be only a slight bit smaller then the balloon so that it rips on the sand paper as it falls through. Do a couple practice drops.
Edit: you want to buy a small balloon and over inflate it to the point that it is almost going to pop on its own regardless how you pop it this will make it easier.
and shouldn't this be posted in help/advice?
I was thinking the whole would probably be between 2/3 and 3/4 the balloon size. We're basically trying to maximize friction. Will a regular brick be heavy enough?
If your balloon is over inflated enough and/or you drop it from a sufficient height a single brick will be heavy enough. There are a lot of parameters, you need to decide which are easier to maximize (hight of drop/weight of brick/...) and do some trial and error to see what works, since its faster and more reliable (in my experience) then equations when it comes to balloons.
Yeah, I'm thinking double digits. I believe the most course grit is 40.
My concern is that "common sense" or, more specifically, laymen guessing, is often contrary to scientific actuality.
Hmm, well...the weight of the brick is probably the easiest to increase. After all, I can stack two bricks on top of each other, and tie them both together, and to the balloon. I'm figuring a piece of string tied to the balloon (perhaps reinforced with superglue) will be the strongest way to secure the balloon.
I wonder if a mechanically driven air pump could be powerful enough... have the brick open a spigot that turns a waterwheel that drives the air pump that creates a low enough air pressure in a sealed container to pop the balloon contained in it.... You could even get it equation precise.
QEDMF xbl: PantsB G+
The sandpaper idea is cute but it might just be easier to have the pendulum knock something over onto the balloon.
We'd considered dropping the brick on it, and slapping it between two pieces of wood. The concern is the "bounciness" of the balloon. In order for the balloon to be easier to pop, the rubber has to be stretched thinner, which means the balloon needs to be bigger, which means it's bouncier. We don't think we'd be allowed to just tape the hell out of it to keep it on place, and even if you do, the tape actually reinforces the rubber, so that becomes a problem. Also, with dropping things on it, how would you trigger that? We all thought it'd be a great idea (two pieces of wood affixed to hinges, that drop and clap together, onto the balloon), but we couldn't figure out how you would trigger that.
For the record, we're allowed to use nails, screws, and other fastening devices to secure the device together, but they can't be exposed. It's a safety concern, the device has to be built so that people won't accidentally cut themselves on anything.
You could also use a CO2 cartridge
took out her barrettes and her hair spilled out like rootbeer
A pin. Think grenade.
took out her barrettes and her hair spilled out like rootbeer
Sounds quite interesting though - forcing the balloon through a too-small hole is a novel approach.
Another unusual method could be something that sucks the air out of a chamber - though that might run afoul of the rules because at some point before it pops, the balloon will be bigger than the regulations.
Equations yo:
Assume that h = 0 at the end point of the pendulum, or in crappy ASCII:
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O __ h = 0
As we know the pendulum is initially at rest, our equation simplifies to
Assuming ϑ represents the angle between the pendulum vertical and its placement at rest, and L is the length of the pendulum,
Putting it all together, considering momentum = mass * velocity:
Determining the momentum needed is a bit more of a pain.
Also ideas we'd considered, potential problems are basically reliability, such as:
1) How do you activate the pump/CO2 cartridge "remotely" ? By remote, of course, I mean, what sort of contraption would be able to trigger the air pump or cartridge?
2) How do you construct a reliably air-tight chamber to do this in? The device will have to be used multiple times, so pre-building it set up, and sealing the outside won't work, because it has to be repeatable.
Once you start the device, no human intervention is allowed.
Rube Goldberg device = you do something, that triggers something, that triggers something else, which in turn makes something else happen, which causes something completely unrelated to what you originally did to pop the balloon.
At least five steps are required for the contest. Must run between 30-120 seconds, at no point can the device (including the balloon, after being popped) exceed 3' x 3' x 3'
Should I add that to the OP?
Also, although we haven't decided fully on the exact method we'll use, I'm leaning heavily toward sandpaper-hole (that sounds horribly wrong), but I'm open to input, though I'd prefer input on how to make this method as reliable as possible.
I fail at reading :P In that case freeze it with an aerosol or turn on a lightbulb next to it.
Wouldn't that qualify as a chemical reaction?
Again, all, let me re-iterate, great suggestions HOWEVER, we want to test the viability of this method FIRST.
So, is there any way to figure out the optimal hole size, relative to the size of the balloon, to break it? This isn't exactly something we can do through trial and error, without taking a ridiculous amount of time and resources to test. Having to cut progressively larger holes into a piece of wood is somewhat preemptively time consuming. Further, if we test sizes from, say, 25% to 75%, and it turns out 67% was optimal, we're somewhat screwed.
The other thing that springs to mind is a two-by-four on a track or hinge with a bucket attached to the end. Create a mechanism for dropping something heavy enough into the bucket and bam, 2nd-class lever action. (water, a bowling ball, anything)
That makes sense. How many successes would you say are required for proof of reliability? In other words, if, say, 30% works once, and we do it again, and it works again, would you say that's reliable? Or should we run it, say, 3-5 times? If it doesn't pop the balloon, we kind of get a really bad score.
This goes for pretty much anything.
I dont' think that's a chemical reaction, that's a pressure difference causing a change in temperature. When the aerosol leaves the can it expands rapidly thus lowering its temperature greatly. Those air canisters to clean keyboards get really cold if you spray them upside down. Also, if you turned on a lightbulb next to it that would eventually work.
you can buy packs balloons at a dollar store. I'd test 10 or 15 at least.
Also you're going to need to secure the brick to the balloon with 30lb test fishing line so the line won't break from the force.
I'd be satisfied after only a few, but that's just me. Balloons aren't going to have significantly different compositions from each other from the same pack. You might want to try a few different brands so you can find one that pops easy.
You do get to supply your own balloon, right? That would be a pretty shitty thing for the prof to do; surprising you on testing day.
Alternatively, just make a machine that will set a fire, and pop the balloon that way.
That might actually take a step out of the issue (if that's desirable). The line itself could deform the balloon sufficiently to deform the balloon if it could be caused to pull the line through the balloon. Those things hurt (but could be termed sharp).
What is being graded here? I can see several lessons behind this... design, reliability, creativity, but the most obvious would be to KISS, especially at the very start of an Intro to Engineering class. Is complexity good?
QEDMF xbl: PantsB G+