[0450] Under A Killer Balloon: Episode 1, Page 8
└ posted on Monday, 28 January 2013, by Novil
Update on 7 February 2013: I updated Sandra’s dialog in the first panel since the original description of the puzzle was probably not precise enough. It’s been a long time since I had physics in school…
- Sandy South: Two similar looking metal rods lie on a table. One of them is magnetic, the other one is not. I have no tools and mustn’t take the bars off the table. How can I find out which one is magnetic?
- Sandy South: As strange as it may sound, if I don’t solve this tricky puzzle soon, I may never find out who stole Cloud’s action figure.
- Qoo: Shouldn’t we have a second look at the scene of the crime?
- Sandy South: Excuse me, but I can’t do physics homework and solve crimes at the same time!
![[0450] Under A Killer Balloon: Episode 1, Page 8](/comics/2013-01-28-0450-under-a-killer-balloon-episode-1-page-8.png "[0450] Under A Killer Balloon: Episode 1, Page 8")
Too many of these solutions assume that what is being stated is that one of the rods is a magnet, and the other is the same metal but not magnetized.
That is not what the question states. It says that one is magnetic and the other is not. While we can assume the one that is magnetic is actually a magnet, we cannot assume that the one that is not can become one, or is effected by one.
We must assume that the one that is magnetic is actually a magnet, because otherwise the problem becomes virtually insolvable.
@ shadow walker:
a quarter is not affected by a magnet.
Jonadab wrote:
I plead guilty to both being over the age of 50 AND amusingly misinterpreting the statement! 🙂
Physics-fail on my part – I assumed the question was one of which demonstrated paramagnetic forces, not “find out which one is a magnet.” In other words, I thought it was: two rods are on a table – one will react in a paramagnetic or ferromagnetic field, the other will not, such as a steel rod and an aluminum rod versus two rods are on a table – one of which is a magnet…
I liked the answer though that someone else had of raising the temperature of the table above the Curie point for the metals. “Hah! Neither of them are magnets now!” Although that would require tools…
@ JDad:
Not shocking at all. The only people who get shocked over what childern can learn and when are people who are afraid of the subject and had a teacher who was afraid of the subject. I introduce the basics of programming to kids as young as 7.
If you strip much of the ‘re-create formulas and laws’ work that is the bulk of most high school and intro college level physics and instead focus on use and applications of formulas it’s no worse then seeing a 7th grader do algebra or even geometry. It’s just math…. oh don’t faint. Shesh, people are too traumatized by K-5 math-phobic math instructors.
Don’t ask 7th grades to derive Newton’s gravitational formula, just have them use it. Give them a teacher who loves the subject, isn’t afraid of it, and who actually understand where C and B students will struggle with the material. You can explain the deeper theory later in high school when you go into covering how it’s not quite accurate and how modern physics has improved on it.
Seriouslly people in the US need to start pulling up their big boy pants when it comes to science education and childern. It’s like people are stuck in the 1950s…. Oh wait… that’s where most school funding is stuck…. or maybe its 1900s level, I not sure, cut backs on the history budget and all that.
@ …:
How do you dress, if you have no other clothes?
@ LuckyStar7:
Every action has an equal and opposite reaction.
@ Frank:
She has to solve the problem… without wearing anything… that has metal on it.
And if her blood tests positive for iron, she will be disqualified faster than you can say Tour de France Armstrong.
So, you roll one towards the other . . . the one that snaps onto the other is magnetic! Or get some nails, throw those on the table and watch which bar the nails move to.
The “Under a Killing balloon” gag is starting to get a little too long, if you ask me. And i’m an owner and big fan of “Under a Killing Moon”…
@ JDad:
It’s not that uncommon… I did physics/biology/chemistry and geography at the same age…
(assuming we’re both thinking of the first year of high school, here)
@ Kazekage:
No, it’d just involve having very strong muscles and a hilarious regard for your own safety.
Besides, you could rub the rods against each other.
@ tahrey:
Uh, hilarious DISregard I mean
@ Darth Killer:
Dude, it’s known as a storyline. If you don’t like it, go read Garfield. And stay the heck away from Gaia (and about 50% of all other webcomics).
demarion wrote:
Wouldn’t the nails count as “tools”? Or are we only considering things like hammers etc?
Also, rolling them towards each other… the effect would be the same on both rods. Even if you held each one still in turn.
m is for wolf wrote:
Hmm, I don’t think that was stated. You could be wearing something with a zipper or metal clasp on it as a completely normal part of a school uniform or other tweenage outfit.
In fact, your average school table has metal legs, and a rod that’s stood on end, resting on the leg of a table that’s been turned on its side could still be said to be “on” the table. You can try and judge, therefore, which one is magnetic by seeing which takes more force when initially lifting one end off the leg (towards a 45-degree position with one corner still touching), and which takes less force moving from the 45 degree to standing up position. Maybe even which one sticks to the leg better if you try and roll them around it… (making sure one end is always pressed firmly against said leg)
Wait, what? They detected plenty enough iron in my blood last time I donated a pint…
Whether your average magnet would be anywhere near strong enough to cause red blood cells to migrate towards / stick to it whilst leaving most of the rest of the plasma behind is less certain. Also, how do you propose breaking the skin?
@ Dorje Sylas:
This, plenty of this. Just because your local educational system is horribly dumbed-down and focussed on producing burger flippers, football stars/cheerleaders and copious cannon fodder doesn’t mean it’s the same situation everywhere 🙂
I just looked up diamagnetism and damn near broke my brain.
ANYWAY… We now know the answer (or at least I do after discovering the “older comments” button), but to carry on the discussion of possible, outside the box alternatives…
Crestlinger wrote:
Sambo wrote:
Depends on how strongly magnetised it is, and the coefficient of friction between the table and the rod. It could go either way, as the independent constants are rather variable in 7th grade level physics. Either the teacher will have you assume that there is effectively no friction, so the non magnetised one will spin basically forever whilst the magnetic one is gradually slowed, or that the magnetic effect is much weaker than the frictional one and therefore you won’t be able to measure the difference.
Greenwood Goat wrote:
Well that’s the actual answer. Pretty clever, too… I don’t think we ever covered this in my OWN Physics education (and I took that thru to 12th/13th grade, plus some postgrad stuff).
We are however assuming that the non-magnetic metal rod is one that actually demonstrates some kind of meaningful magnetic attraction, and isn’t e.g. Aluminium. (I’m pretty sure there should be some magnetic metals that look similar, in rod form, to a rod of Al with a thin layer of AlO on its surface?) … And we’re not dealing with e.g. Chromium and a rod of plastic / aluminium with a cosmetic but magnetically insignificant chrome-plate layer on the outside.
All school physics, and a lot of realworld theoretical physics, deals in gross simplifications of the actual situation. We’re only concerned here with magnetism that can be detected without complex tools. The magnetic field strength of the “non-magnetic” rod won’t come anywhere close to that of the “magnetic” rod without a lot of work trying to transfer the magnetism. Simply touching one to the other won’t do it; at least, not in any meaningful or lasting way.
A parked car sitting on the surface of the earth is actually moving at 1000mph (or more likely somewhere around 40,000 to 42,000mph all things considered), but if we were to look at it in the reference frame of it moving vs the easily observable universe, we’d say it was stationary. The wheels aren’t going around…
Antonio R wrote:
Hmm, I was wondering when someone might come up with an Eddy Current type solution… nice thinking. It does however require another one of those frictionless tables, unless we’re dealing with a fairly strong magnetic effect.
Overall it’s a similar idea to the “official” solution but without the bars actually touching.
(As a bonus, you could also try and hook up some kind of simple, nonpolarised, battery powered device to one rod then the other (light bulb/rectified LED, motorised pocket fan, etc), using a set of jumper leads, as you spin one then the other, and see which of the four attempts caused it to turn on… As you’ll definitely be generating some kind of electric force/charge/current with this experiment)
Max Goof wrote:
That’s a valid complaint, but seeing as the strip is written and drawn by two people for whom English is a “second language”, and the words are also being said by a tween reading from a lower-level school textbook (which aren’t famous for absolute accuracy…), we can probably let the difference between “magnetic” and “magnetised” slide…
@ Marmota:
In Maryland of the United States, we can start Physics in Grade 11. No other physics is taught until then, but most people have a basic understanding of it by then…
@ Jonadab:
Not guilty. Just familiar with the Queen’s English.
@ Hielario:
Use your head, you blinking idiot. I was obviously speaking only of footwear, not clothes in general.
@ Chino:
Still reacts to the magnet. And boots are footwear, not tools. Screw your loose definition of ‘tool’ for the sake of demonstrating one specific property of magnetism.
Also, I’ve seen magnets stick to steel before (specifically steel tools).
Rub the bars together unidirectionally. Then they’ll both be magnetised.
Or bash them hard enough together, and neither of them will be.
Not the sort of elegant answer the others provided… but I like cheating.
Sambo wrote:
Hmmm…well this is physics, that means the rods are lying on a frictionless table in a vacuum. So if the rods are rotated, eventually one will slow down…the magnetized one.
But then in this scenario that would make this a trick question…because the experimenter would be dead from hypoxia.
L@ Robert:
Love Robert’s comment about the nature of tools and interactions xD. Anyway, just wanted to point out that there’s a mistake in the transcript. It says “magnetic” instead of “magnetized” 😉
Andrew wrote:
I think the image was updated. It is currently modified Feb 6, despite the page being Jan 28th.
Greenwood Goat wrote:
Correct solution, but there is another weird issue to consider. If the magnetic field runs lengthwise down one rod, then the ends of that rod will attract the middle of the other. On the other hand, if the magnetic field is perpendicular to the length of the rod, then I think any part of either rod will attract any part of the other. I would not expect to encounter the second form — unless you got the rods from Larissa, or maybe Ye Thuza.
I think the test with the perpendicular field rods would be (assuming cylindrical rods as depicted) that the magnetic rod being dragged from the center by the nonmagnetic rod will not roll, while the non-magnetic rods would roll. (Gee, I need a frictional surface.)
People need to pay attention before they comment. Woo is called Qoo in this mini-series. No need to keep asking why.
Also, the physics problem clearly stated to similar looking iron rods, so both are magnetic but one is magnetized and one isn’t. Without tools (including zippers and other metal accessories) and without lifting them off the table, I think the other commenter’s method is the correct one.
The magnetic field is strongest at the poles ad weakest in the middle, so putting them in a T formation and seeing which attracts the other the strongest in which position will determine which is the magnet.
Max Goof wrote:
Assuming one is taking the old “touch the end of one to the middle of the other” routine and it turns out they don’t even stick (because one doesn’t have magnetic properties), then necessarily the two are made of different materials and unless both of them had very similar physical properties (besides the magnetism-based ones) then you could simply examine them and move them around on the table a bit to discern which one was magnetic (since there aren’t that many magnetic metals).
I notice that half a dozen or more people are saying “just test them with a piece of metal!”
…Seriously? Do you honestly think you’re being clever? Because if so, that’s just sad. Obviously if you have a piece of metal it’s trivial to check which is the magnet, so clearly you’re not supposed to use anything but the rods themselves. Introducing extra things into the situation just makes you look like a fool, for who else would expect people to be impressed that they know that a magnet attracts metal?
If the answer is supposed to be “Touch one end to the other’s center. If it attracts, the touching end is magnetized.”, well, that is WRONG, because screw you, I magnetized the rod in some radial direction.
And stop mixing up “magnetic” and “magnetized”. I see that is the correction from the original dialogue… it’s still in the searchable text.
Argh, just don’t give children fickle, underdefined exercises that lead to oversimplified answers. Not even in a comic, unless you make fun of it / show the problem. T_T
Ola
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