Physics puzzle
Poll
 | 20 votes (58.82%) | ||
| | 5 votes (14.7%) | ||
| | 1 vote (2.94%) | ||
| | 8 votes (23.52%) |
34 members have voted
January 6th, 2012 at 1:48:54 PM
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Imagine a helium filled balloon floating inside a car.
If the car starts to accelerate, where will the balloon move with respect to the car?
If the car starts to accelerate, where will the balloon move with respect to the car?
"When two people always agree one of them is unnecessary"
January 6th, 2012 at 1:59:48 PM
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wow, different answers. Since I might feel foolish, I won't say yet how I voted [g]
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January 6th, 2012 at 2:08:34 PM
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I voted for forward, but I'll explain why after more results come in.
"For with much wisdom comes much sorrow." -- Ecclesiastes 1:18 (NIV)
January 6th, 2012 at 2:11:38 PM
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It has to be backward. I have a perfectly good explanation why. Maybe I'm even right. Or maybe not.
January 6th, 2012 at 2:11:41 PM
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If the car accelerates, the air inside the car will be pushed back through inertia, just as you would be pushed back into your seat. My guess is that as the helium balloon is lighter than the air surrounding it, if the air is pushed back, the balloon will be pushed forward. If the car swerves left, the balloon would also move left as the air through centrifugal force is pushed to the right.Quote: weaselmanImagine a helium filled balloon floating inside a car.
If the car starts to accelerate, where will the balloon move with respect to the car?
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January 6th, 2012 at 2:22:31 PM
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I'm drinking a cup of tea as I read this, and there's a small leaf floating in my cup. When I pick up the cup and accelerate it in a straight line, the leaf doesn't move at all (aside from the shaking due to my unsteady hand).
I think the balloon doesn't move either.
Edit: I assume the car accelerates due to an outside force, and that nothing else inside the car changes (e.g. the position of a driver).
I think the balloon doesn't move either.
Edit: I assume the car accelerates due to an outside force, and that nothing else inside the car changes (e.g. the position of a driver).
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January 6th, 2012 at 2:28:27 PM
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I voted, but will not reveal why I voted as I had.
I've seen this question before, albeit it was the car makes a right turn, which way does the balloon move...
I've seen this question before, albeit it was the car makes a right turn, which way does the balloon move...
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January 6th, 2012 at 2:35:10 PM
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I added to the red line at the top of the poll.
Many people, especially ignorant people, want to punish you for speaking the truth. - Mahatma Ghandi
January 6th, 2012 at 2:45:23 PM
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The helium makes the difference.
A falling knife has no handle.
January 6th, 2012 at 2:45:58 PM
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Quote: weaselmanImagine a helium filled balloon floating inside a car.
If the car starts to accelerate, where will the balloon move with respect to the car?
Ha! I was just thinking something similar. Being that it's winter here, I've noticed that whenever I brake or turn sharp, I can feel a wave of hot air wash over me. And since I've been thinking of that lately...
It would move forward. Cold air on the floor runs backwards, displacing the hot air already back there. The hot air would move forward, and since hot air is up high, and the ballonn's up high, it'd get carried along with it.
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January 6th, 2012 at 2:56:51 PM
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My first intuition is that it would move backward, like everything else inside the car. Then I thought that maybe it wouldn't move because the mass of air in the car wouldn't move. Then I realized that the mass of air in the car will move (like everything else in the car) and there will be a higher density of air in the back of the car. This lead me to my final answer: the balloon moves forward, toward the lower density of air.
Still, I'd like to see it to believe it.
Still, I'd like to see it to believe it.
I heart Crystal Math.
January 6th, 2012 at 3:01:18 PM
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Because the balloon is lighter than air, and you are
heavier than air, the balloon moves in the opposite
direction you do. I know because I used to deliver
balloons for a business we had 30 years ago.
heavier than air, the balloon moves in the opposite
direction you do. I know because I used to deliver
balloons for a business we had 30 years ago.
"It's not called gambling if the math is on your side."
January 6th, 2012 at 4:18:53 PM
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OK, now I'll explain my theory. Lighter and heavier than air are only valid in relation to gravety. Since the balloon has some mass it will behave the same as anything else with mass and move back. And yes it will continue to try to move up but the top of the car will prevent it. If it was a convertable the balloon would float up and the car accelleration would not matter. Why should the top of the car matter?
January 6th, 2012 at 5:10:22 PM
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Quote: weaselmanImagine a helium filled balloon floating inside a car.
If the car starts to accelerate, where will the balloon move with respect to the car?
Are the windows open? Is the balloon resting against the ceiling (as loose helium ballons are apt to do in a car at rest) or, is it partially filled so that it is suspended in the free air?
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January 6th, 2012 at 5:48:47 PM
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Quote: weaselmanImagine a helium filled balloon floating inside a car.
If the car starts to accelerate, where will the balloon move with respect to the car?
Neither of the above. A definitive answer can not be determined based on the data provided alone.
So, based on this data: It can move forward, backwards, first forward and then backwards, first backwards and then forward, and in all cases sideways.
The air column in the back of the car is being compressed by the rear window, and resulting air motion in turn transfers force to the balloon. This is done aerodynamically (drag) and hydrostatically (lift).
Hydrostatic force, as has been stated, is directed forward relative to the car, provided the windows are closed. If the rear windows are open, suction can depressurize the rear of the car and direct it backwards. Since the hydrostatic force is very small (milligrams, given the small pressure difference), analyzing hydrostatic behavior alone is not useful. Analyzing it would be in the spirit of puzzle traditions of only using elementary school physics, but 'elementary school physics ruleset' != 'physics', so that would not be a physical answer.
Aerodynamic force in a sealed car will be directed forward relative to the road, but backwards relative to the car. Aerodynamic force will push the balloon in the same direction as the air around it. If the car leaks air, as most cars do, external air will be entering it through the front and escaping through the back, carrying the balloon with it. Quantitatively, the aerodynamic force is on the order of [0.01...0.05] kg/(m/s) depending on balloon size, which is multiple grams, allowing hydrostatic force to be ignored entirely.
The exact outcome depends on the car's internal geometry, on whether any windows are open and which, on acceleration rate, and, generally, on air currents inside the car.
If a one-word answer is required to what behavior is most likely, it's outward (towards the sides/windows). Out of answers on the poll, "sideways" is closest.
And it doesn't even affect the outcome at all whether the balloon is filled with helium or ambient air.
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January 6th, 2012 at 6:03:01 PM
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Gravity is acceleration. The basis of Einstein's Special Theory of Relativity rests on the postulate that light travels at the speed of light in all frames of reference and that gravity is the same as acceleration. Therefore, if you are in an enclosed box in a rocket ship in outer space that is accelerating at 10 meters per second per second, you would not be able to tell the difference if you were inside a similar box on the Earth's surface. There is no experiment that you can do within the confines of that box that will tell you if you are on a rocket ship of merely on the ground.Quote: downtownerOK, now I'll explain my theory. Lighter and heavier than air are only valid in relation to gravety...
That was a long way to go to let you know that "Lighter and heavier than air are only valid in relation to gravety" is incorrect.
Someday, joor goin' to see the name of Googie Gomez in lights and joor goin' to say to joorself, "Was that her?" and then joor goin' to answer to joorself, "That was her!" But you know somethin' mister? I was always her yuss nobody knows it! - Googie Gomez
January 6th, 2012 at 6:24:53 PM
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Quote: s2dbakerGravity is acceleration. The basis of Einstein's Special Theory of Relativity rests on the postulate that light travels at the speed of light in all frames of reference and that gravity is the same as acceleration.
This is (almost) spot on. "Almost" because (1) Special Relativity specifically excludes gravity (it is the General Relativity you should be referencing), and (2) gravity is equivalent to inertia rather than acceleration (gravity is a force, acceleration isn't).
But the idea is exactly right - accelerating car is (locally) indistinguishable of a stationary one in a gravitational filed directed towards its back. The helium balloon will float forward because of buoyancy.
P90: Nice analysis ... I am not really sure how to respond to that, other than to suggest that you buy a balloon, put it in a car, and floor the gas :) The factors you mentioned are all real, but not very significant in this case. It'll float forward.
"When two people always agree one of them is unnecessary"
January 6th, 2012 at 6:28:43 PM
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weaselman's talking about gravity again...
Cue the Doc! ;)
Cue the Doc! ;)
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January 6th, 2012 at 6:30:36 PM
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Quote: Faceweaselman's talking about gravity again...
Cue the Doc! ;)
s2dbaker was the one who started it :)
I am sure, there is a non-relativistic explanation too (I mean, it's unlikely this fact has not been known/explained before Einstein). CrystalMath actually came quite close to providing one.
I just think that the relativistic one happens to be the most elegant and simple ...
"When two people always agree one of them is unnecessary"
January 6th, 2012 at 6:36:34 PM
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D'oh! /homerQuote: weaselman..Special Relativity specifically excludes gravity (it is the General Relativity you should be referencing)..
Someday, joor goin' to see the name of Googie Gomez in lights and joor goin' to say to joorself, "Was that her?" and then joor goin' to answer to joorself, "That was her!" But you know somethin' mister? I was always her yuss nobody knows it! - Googie Gomez
January 6th, 2012 at 6:40:58 PM
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If you guys are so smart how come no one can tell me why my solution to the NYT math problem worked?
https://wizardofvegas.com/forum/off-topic/off-topic/7707-math-puzzle-from-nytimes/3/#post113682
https://wizardofvegas.com/forum/off-topic/off-topic/7707-math-puzzle-from-nytimes/3/#post113682
January 6th, 2012 at 6:51:18 PM
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Who said we were smart?Quote: downtownerIf you guys are so smart..
Someday, joor goin' to see the name of Googie Gomez in lights and joor goin' to say to joorself, "Was that her?" and then joor goin' to answer to joorself, "That was her!" But you know somethin' mister? I was always her yuss nobody knows it! - Googie Gomez
January 6th, 2012 at 6:57:56 PM
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The balloon will always move in the direction required to obscure the driver's view of the road.
January 6th, 2012 at 7:20:33 PM
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Quote: weaselmanP90: Nice analysis ... I am not really sure how to respond to that, other than to suggest that you buy a balloon, put it in a car, and floor the gas :) The factors you mentioned are all real, but not very significant in this case. It'll float forward.
I think that's the only way to resolve it, specifically to test it honestly rather than with the intention to get at the "right" answer.
Have to disagree with the statement that the factors are not very significant.
Take an "elementary" balloon, with volume of 1 dm^3 and frontal area of 1 dm^2. Reynolds number will be 1-2 for these speeds. That is a force of 5-10 grams at 1m/s wind velocity. Balloon's lift is 1.2 grams, of which part is the shell, leaving 0.4-0.6 grams for acceleration of 1g. A car accelerating at (27m/s)/4s produces 0.68g. And that's if you aren't leaking air, otherwise the pressure will equalize. So a force of ~0.3 grams can be expected, meaning a draft of only 0.25m/s is stronger than the hydrostatic force. Larger balloons have more hydrostatic force relative to hydrodynamic, but it's only linear.
Seeing how it's a well-known puzzle, I looked online for videos. Most cheated by tying the balloon to something on the floor (which isn't part of the puzzle). Those who didn't tie it to the floor, got it flying all over the place. The answer when you tie the balloon down is, strictly speaking, "stay put", as it returns to the original position.
Try opening some of the windows, or tying the balloon to the floor, but taking the top down, and I'm sure you'll see a difference even with slow driving.
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January 6th, 2012 at 7:38:23 PM
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The first time I delivered a bunch of balloons in the van,
as soon as I took off they were all up front with me and
I couldn't see out the windshield. I learned to keep a
steel bar in the back and wrapped the strings around it.
as soon as I took off they were all up front with me and
I couldn't see out the windshield. I learned to keep a
steel bar in the back and wrapped the strings around it.
"It's not called gambling if the math is on your side."
January 6th, 2012 at 9:18:42 PM
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Quote: s2dbakerWho said we were smart?
Somebody was refering to Einstein's relativity in an everyday experience without even approaching the speed of light. I'm only disapointed no one brought up how quantum mechanics impacts the balloon's trajectory. Doesn't chaos theory apply at all. I'll bet if we look at the movivation of the balloon and the car we can come to a Nash equilbrium somehow.
January 6th, 2012 at 9:35:21 PM
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The ballon would move any way you want it to. You were told to imagine a balloon. So the balloon only exists in your mind and will therefore move anywhere you want it to.
I know this isn't what the questioner was going for. I just wanted to reveal an unseen flaw in the question. To tell the truth I cheated and googled the answer.
I know this isn't what the questioner was going for. I just wanted to reveal an unseen flaw in the question. To tell the truth I cheated and googled the answer.
January 6th, 2012 at 9:54:37 PM
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Quote: TheNightflyThis should settle it...
Tied up. Not in the conditions.
The puzzle doesn't specify they are tied up, doesn't specify smooth driving, doesn't specify the windows can't be opened.
I mean, there is no doubt that if you isolate the hydrostatic force, it acts per the puzzle giver's intended "right" answer, but such a puzzle that divorces practical conditions in favor of a textbook answer is not in good taste.
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January 7th, 2012 at 6:35:41 AM
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Quote: P90
Tied up. Not in the conditions.
The puzzle doesn't specify they are tied up, doesn't specify smooth driving, doesn't specify the windows can't be opened.
I mean, there is no doubt that if you isolate the hydrostatic force, it acts per the puzzle giver's intended "right" answer, but such a puzzle that divorces practical conditions in favor of a textbook answer is not in good taste.
Consider this puzzle. "A scale is located on the floor of an elevator, that is being pulled up with a constant acceleration of 1 meter per second per second. What will the display show if you put two 32 kilogram weights on it?"
Certainly, you would find it in bad taste too, because it does not specify the time of day and moon phase to properly account for moon and sun gravitation (the latter also requires calendar date), nor the longitude, which is necessary to compute the centrifugal force due to Earth rotation, nor the volume or density of the weights to account for the air buoyancy. There is also no mention of how far from the surface the elevator is located, or on which planet (if it is on a planet at all, and not in deep space or underground). The spring constant of the line, pulling the elevator up, and the current level of its deformation are omitted too. Also, how are the weights put on it? Are they both level on the scale or do you put one on top of the other? What shape are they? Would they just fall off from the scale? Is the elevator filled with water by any chance? Or, perhaps, liquid lead?
Hell, it does not even specify which display it is talking about, could be a thermometer on the wall! Besides, when it says "pulled up", how can you be sure it does not really mean "pushed down"? Is the floor actually fixed to the elevator? Maybe, the elevator is being pulled up, but the floor remains stationary, or is free falling? Also "up" is so ambiguous. The direction you consider "up" could really be "down" for someone in China.
"When two people always agree one of them is unnecessary"
January 7th, 2012 at 6:52:00 AM
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Quote: weaselmanCertainly, you would find it in bad taste too, because it does not specify the time of day and moon phase to properly account for moon and sun gravitation (the latter also requires calendar date), nor the longitude, which is necessary to compute the centrifugal force due to Earth rotation, [..]
So I found a solution for the helium balloon in a car problem, but it only works for spherical cars in a vacuum :P
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January 7th, 2012 at 6:52:42 AM
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Quote: weaselmanCertainly, you would find it in bad taste too, because it does not specify the time of day and moon phase to properly account for moon and sun gravitation (the latter also requires calendar date)
Not the same.
It's not a matter of precision, but that you need particular conditions for this school experiment to show the point it's intended to teach, rather than fly all over the car.
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January 7th, 2012 at 6:54:14 AM
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Quote: P90Not the same.
It's not a matter of precision, but that you need particular conditions for this school experiment to show the point it's intended to teach, rather than fly all over the car.
The other puzzle is not a matter of precision either. It's a matter of assumption. If the floor is not fixed to the elevator, the answer will be very different for example. Or if the elevator is actually located in deep space ... or filled with liquid lead.
You don't need too many "particular" conditions to see that the balloon in an accelerating car will move forward. Like I said before - just go to a store, buy a helium balloon, put it into your car and drive, without paying special attention to any conditions. See where it moves when you start. Or just ask EvenBob :)
"When two people always agree one of them is unnecessary"
January 7th, 2012 at 7:12:19 AM
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Is it OK if I do it with the top down?
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January 7th, 2012 at 7:21:22 AM
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Quote: P90Is it OK if I do it with the top down?
Only if you think, that that's how most cars usually drive, and that that's the most reasonable assumption you can make about this puzzle.
That would be an equivalent of detaching the elevator floor from the walls.
"When two people always agree one of them is unnecessary"
January 7th, 2012 at 7:28:27 AM
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If a car being driven with its top down or its windows open is as rare a sight for you as an elevator with its floor detached... have you by any chance ever contemplated changing your nickname to Wizard of Ross Island?
The question of whether the car is operating as a sealed volume or not is completely relevant to the "puzzle". In both cases the balloon will be moved due to the same principles, but in opposite directions.
I know which option should be picked in a school test, but the puzzle you are solving in such tests is "which option was the test author most likely to mark as correct", not the question as formulated, and we are not in school.
The question of whether the car is operating as a sealed volume or not is completely relevant to the "puzzle". In both cases the balloon will be moved due to the same principles, but in opposite directions.
I know which option should be picked in a school test, but the puzzle you are solving in such tests is "which option was the test author most likely to mark as correct", not the question as formulated, and we are not in school.
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January 7th, 2012 at 7:58:11 AM
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Quote: P90If a car being driven with its top down or its windows open is as rare a sight for you as an elevator with its floor detached...
It's a qualitative thing. Just knowing that the condition is not common is enough to conclude that the assumption is unreasonable. The actual degree of rareness is irelevant. If the puzzle needed you to assume an uncommon condition, it would specify it explicitly. Lacking that, you have to assume otherwise. Being able to make reasonable assumptions about unspecified conditions is a skill as important for real life problems as knowing the formulas.
"When two people always agree one of them is unnecessary"
January 7th, 2012 at 7:58:15 AM
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Quote: P90If a car being driven with its top down or its windows open is as rare a sight for you as an elevator with its floor detached...
It's a qualitative thing. Just knowing that the condition is not common is enough to conclude that the assumption is unreasonable. The actual degree of rareness is irelevant. If the puzzle needed you to assume an uncommon condition, it would specify it explicitly. Lacking that, you have to assume otherwise. Being able to make reasonable assumptions about unspecified conditions is a skill as important for real life problems as knowing the formulas.
"When two people always agree one of them is unnecessary"
January 7th, 2012 at 8:54:19 AM
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Quote: weaselmanJust knowing that the condition is not common is enough to conclude that the assumption is unreasonable. The actual degree of rareness is irelevant.
In that case, would you consider the question "What happens when you have an ace and a 10?" (sic) to be adequately answered by "You win"?
Quote: weaselmanBeing able to make reasonable assumptions about unspecified conditions...
Like I said, I know which box to tick if I see it on an elementary school test.
Such a question is clearly below this forum's level.
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January 7th, 2012 at 10:05:40 AM
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I think the Wizard draws some secret pleasure from trying to get me involved in disagreements -- he sent me a PM this morning asking me to take a look at this thread, apparently right after the arguments started getting petty and a bit outlandish.
The first time I recall discussing this topic with my family was when my two sons were quite young. We had just left an amusement park, and one of them had a helium-filled balloon on a string. As I started to drive, I asked him, "Which way will the balloon go if I have to stop the car?" His reply was a slightly puzzled, "Out the window?" He assumed that I had meant the scenario of my having to stop the car because the balloon was blocking my vision, with the result being that I would make him throw the balloon away. I'm not really quite so evil as my family believes.
Yep, assuming that people don't try to dissect every sentence of the problem and instead just read it as it is rather obviously intended. I think this problem is clearly intended in the realm of Newtonian physics. Acceleration of the car results in the air inside (due to inertia plus gravity) tending to move toward the floor of the car and toward the rear of the car (in relation to the car's moving position) to the extent they can. The helium-filled balloon and all other objects in the car that have mass would have the same tendencies. However, because the balloon is floating on the air (assuming that it was floating in the air and restrained by a string prior to acceleration), it would be bypassed by the air and would float toward the front and toward the ceiling of the car during the acceleration.
Now if you want to consider variants in which there is no string restraining the balloon, windows or top of the car are open, or the car is traveling at speeds approaching or exceeding that of light, and expect one answer to apply to all cases, then I'm not interested in being involved in this thread. A couple of you can flag this post so it goes away, and my intrusion might be forgotten.
Have fun with it.
The first time I recall discussing this topic with my family was when my two sons were quite young. We had just left an amusement park, and one of them had a helium-filled balloon on a string. As I started to drive, I asked him, "Which way will the balloon go if I have to stop the car?" His reply was a slightly puzzled, "Out the window?" He assumed that I had meant the scenario of my having to stop the car because the balloon was blocking my vision, with the result being that I would make him throw the balloon away. I'm not really quite so evil as my family believes.
Quote: TheNightflyThis should settle it...
Yep, assuming that people don't try to dissect every sentence of the problem and instead just read it as it is rather obviously intended. I think this problem is clearly intended in the realm of Newtonian physics. Acceleration of the car results in the air inside (due to inertia plus gravity) tending to move toward the floor of the car and toward the rear of the car (in relation to the car's moving position) to the extent they can. The helium-filled balloon and all other objects in the car that have mass would have the same tendencies. However, because the balloon is floating on the air (assuming that it was floating in the air and restrained by a string prior to acceleration), it would be bypassed by the air and would float toward the front and toward the ceiling of the car during the acceleration.
Now if you want to consider variants in which there is no string restraining the balloon, windows or top of the car are open, or the car is traveling at speeds approaching or exceeding that of light, and expect one answer to apply to all cases, then I'm not interested in being involved in this thread. A couple of you can flag this post so it goes away, and my intrusion might be forgotten.
Have fun with it.
January 7th, 2012 at 10:29:07 AM
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Well, didn't mean to heat things up.
I just think it's a little condescending to post an elementary school puzzle on a forum with mostly intelligent people, particularly to do so with nothing but an elementary school answer in mind. Same as how if you ask what is 2+2 on 2+2 forums, you probably aren't doing it to hear "4".
I just think it's a little condescending to post an elementary school puzzle on a forum with mostly intelligent people, particularly to do so with nothing but an elementary school answer in mind. Same as how if you ask what is 2+2 on 2+2 forums, you probably aren't doing it to hear "4".
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January 7th, 2012 at 10:40:46 AM
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My explanation is simple. When the car accelerates everything in it not affixed will be pushed towards the back of the car, because a body at rest wants to stay at rest. However, there is only so much space in the back of the car. Air is heavier than helium, so it will push the balloon out of the way, towards the front.
As the father of three, we have balloons in the car once in a while and I've observed this. Of course I bore my kids with an explanation of why every time.
As the father of three, we have balloons in the car once in a while and I've observed this. Of course I bore my kids with an explanation of why every time.
"For with much wisdom comes much sorrow." -- Ecclesiastes 1:18 (NIV)
January 7th, 2012 at 11:07:22 AM
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Quote: P90Well, didn't mean to heat things up.
I just think it's a little condescending to post an elementary school puzzle on a forum with mostly intelligent people, particularly to do so with nothing but an elementary school answer in mind. Same as how if you ask what is 2+2 on 2+2 forums, you probably aren't doing it to hear "4".
It's overly simplistic to call this an elementary school problem. We must make assumptions and answer questions based on those assumptions. If, however, this forum was composed of physicists, then we would have to clarify every aspect of the problem. For instance, I assumed that the acceleration was positive and that the acceleration was linear and not rotational. It was quite easy to determine the intent of the question, and for most of us, the answer is counter intuitive, which makes it a good problem to reason through.
I heart Crystal Math.
January 7th, 2012 at 11:10:23 AM
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I think we got some serious mileage out of the airplane/treadmill question, didn't we? That one always seems to confound some pretty smart people.
A falling knife has no handle.
January 7th, 2012 at 11:29:24 AM
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I remember in physics class, after watching 2001 A Space Odyssey, discussing the weight felt by the guy running around the space craft ring. Depending on the direction and speed he might weigh a lot or very little. Then there were the Liliputions and Brobdignags from Gulliver's Travels and bone strength and eating to produce body heat. Things get complicated when you leave the perfectly spherical vaccum and enter the real world.
January 7th, 2012 at 12:20:20 PM
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Quote: P90
I just think it's a little condescending to post an elementary school puzzle on a forum with mostly intelligeparticularly to do so with nothing but an elementary school answer in mind. Same as how if you ask what is 2+2 on 2+2 forums, you probably aren't doing it to hear "4".
I don't know what part of it you found ccondescending, it was not my intent. I like this puzzle, because it is an elegant, and somewhat non trivial illustration of the equivalence priciple. Most people I have discussed it with so far (including on this forum) sem to have found it at least amusing.
I am sorry if it turned out to be too simple for your level of fundamental understanding of elementary physics, I guess, I have some growing to do before I can match it.
Not sorry for posting the puzzle though - still think, it was a good riddle for those of us, not quite advanced in these matters as you are.
"When two people always agree one of them is unnecessary"
January 7th, 2012 at 5:41:01 PM
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All I know is if Monty knows where the car is, then you should switch doors.
January 7th, 2012 at 8:34:51 PM
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Quote: downtownerI remember in physics class, after watching 2001 A Space Odyssey, discussing the weight felt by the guy running around the space craft ring. Depending on the direction and speed he might weigh a lot or very little.
I hate to change the topic, but what is the answer? I assume the ring rotated at a speed to exactly simulate earth gravity. My guess is that the runner would feel the same way running in either direction, for the same reason in an airplane it requires the same effort to walk toward the front of the cabin as away from it. Then again, physics is not my area of expertise.
"For with much wisdom comes much sorrow." -- Ecclesiastes 1:18 (NIV)
January 7th, 2012 at 8:37:18 PM
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Quote: CrystalMathIf, however, this forum was composed of physicists, then we would have to clarify every aspect of the problem.
Well, it has its good share of mathematicians, which is close enough.
Quote: weaselmanNot sorry for posting the puzzle though
Never said you should be. I'm just saying - when people post school questions in a non-school forum, they usually expect a more thorough look at them than in the classroom, like figuring out situations where the answer can be different. So it's surprising to me that you only expect unequivocal "box A" and reject any look at variations in conditions as irrelevant.
For one, particularly surprising that you would.
Put it this way: Suppose you were using this setup in a system where the outcome matters. Let's say the balloon is to serve as a hydrogen leak detector, with string deflection triggering emergency tank evacuation. Why do it this way is not up to you. Would you still be satisfied with the same "box A" answer?
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January 7th, 2012 at 8:57:34 PM
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Quote: WizardI hate to change the topic, but what is the answer? I assume the ring rotated at a speed to exactly simulate earth gravity. My guess is that the runner would feel the same way running in either direction, for the same reason in an airplane it requires the same effort to walk toward the front of the cabin as away from it. Then again, physics is not my area of expertise.
It's not my area, either, but all SF readers learn this :)
The answer is he would feel "heavier" if he ran in the direction of rotation, and "lighter" if he ran in the opposite direction. That's because int eh first case he'd be adding to the speed, just as if the ring ran faster. Contrariwise, he diminishes speed if he runs opposite to the rotation, and the effect would be the same as if the ring ran slower.
How much he feels either effect depends on how fast he can run.
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