1. What is the distance of your journey? Express your answer as a function of c, where c = the circumference of the earth.
2. How many revolutions around the earth do you make?
Quote: WizardYou start at any point on the equator and head northwest until you reach the North Pole.
1. What is the distance of your journey? Express your answer as a function of c, where c = the circumference of the earth.
2. How many revolutions around the earth do you make?
I'm not sure I understand the parameters.
Quote: AyecarumbaI'm not sure I understand the parameters.
If you start on the equator and head off at an angle of 45 degrees, you will complete a circle but never reach the North Pole.
If you always travel NW, you angle relative to the latitude will change.
2. You make zero revolutions around the earth, (or maybe that should be 1/4 - from the equator to the pole), but you make several (many?) revolutions around the pole.
Quote: WizardYou start at any point on the equator and head northwest until you reach the North Pole.
1. What is the distance of your journey? Express your answer as a function of c, where c = the circumference of the earth.
2. How many revolutions around the earth do you make?
I'm guessing part 2 is easy.
There will be an infinite number of revolutions around the North pole. I am not sure if they can really be considered "around the Earth", the path will look more like a spiral, converging towards the pole.
As for the total distance, I get c*sqrt(2)/4, I think.
After incorrectly stating the wrong answer to my last math puzzle, I'm not going to say definitively that my answer is right. That said, I think that weaselman has the correct answer to part 1, and ChesterDog to part 2. If you click the spoiler buttons you will get zero credit, unless to verify your own correct answer.
I would guess that the number of revolutions around the pole would also involve infinity.
There is one ant on each corner of a square table of side length 1 meter. Each ant walks at rate of one meter per minute. Each ant directly crawls towards the ant on his left.
2a. How long does each ant crawl before meeting in the middle of the table?
2b. How many spirals around the center does each ant make?
To avoid confusion, please refer to the original questions as 1a and 1b.
Quote: WizardTo those who say you would never reach the North Pole, due to an infinite number of spirals, let me ask this problem #2.
There is one ant on each side of a square table of side length 1 meter. Each ant walks at rate of one meter per minute. Each ant directly crawls towards the ant on his left.
2a. How long does each ant crawl before meeting in the middle of the table?
2b. How many spirals around the center does each ant make?
To avoid confusion, please refer to the original questions as 1a and 1b.
Here is my response:
So, they don't necessarily first meet in the middle.
Quote: WizardLet me clarify that a "revolution around the earth" is the same as a revolution around the north pole. At least for purposes of this problem.
After incorrectly stating the wrong answer to my last math puzzle, I'm not going to say definitively that my answer is right. That said, I think that weaselman has the correct answer to part 1, and ChesterDog to part 2. If you click the spoiler buttons you will get zero credit, unless to verify your own correct answer.
Is the "Pole" a point, or a line?
Quote: WizardTo those who say you would never reach the North Pole, due to an infinite number of spirals, let me ask this problem #2.
Assuming that all of the ants are identical, they all must follow identical spiral paths. So, the only point at which they could possibly converge would have to be the center of the table. However, each ant is continually moving away from the table's center, chasing another ant (to the left) which is traveling away from it.
Each ant represents a point in a constantly shrinking (and constantly rotating) square, that is always centered around the table's center point, regardless of how infinitesimal the square gets.
So, the ants never reach each other and they never reach the center point on the table.
At least, that's how I see it.
To those who say the ants will never reach the middle, consider the function of the distance between adjacent ants by time.
Quote: WizardRegarding problem 2, let me clarify that in the initial state there is one ant on each corner. To those who say the ants will never reach the middle, consider the function of the distance between adjacent ants by time.
Are the ants infinitely small -- like a point?
If you're facing directly north, that's north. If you face one degree westward from north, is that northwest? Does that affect anything?
Quote: tuppAre the ants infinitely small -- like a point?
Yes.
Quote: NareedHow west is northwest?
Assume you have a compass and always head exactly northwest. Meaning the line halfway between north and west.
Quote: NareedIf you're facing directly north, that's north. If you face one degree westward from north, is that northwest? Does that affect anything?
If one is continually traveling away from a point, one can never reach that point.
Quote: tuppIf one is continually traveling away from a point, one can never reach that point.
Sort of like how an infinite string of nines in "0.999999999..." will never reach "1"?
Quote: NareedHow west is northwest?
If you're facing directly north, that's north. If you face one degree westward from north, is that northwest? Does that affect anything?
Northwest (N45W) is exactly 315 degrees clockwise from the North. The direction one degree westward from North is properly referred to as "359 degrees", "minus one degree", or N1W.
Why they measure it clockwise and in degrees, while about any other angle is counterclockwise and in radians, is one of life's little mysteries.
I would imagine, that the distance is a convergence problem. The actual distance should converge to a finite distance. At least that's what I think of conceptually.
My biggest problem is, if you're looking at a person walking, or ants walking on a table, they take up physical space, and the physical constraints prevent them to continue walking, since eventually they would need to make infinitesimally small movements. I realize that's not really the point, but it still bothers me.
Quote:Are the ants infinitely small -- like a point?
Quote:Yes.
I would guess that the spiral path that the points take would always be the same, regardless of their speed.
The points can never overtake each other nor can they reach the table's center. So, to me, it seems that speed and distance (paradoxically) would not affect this outcome.
Quote: tuppIf one is continually traveling away from a point, one can never reach that point.
I would argue that the ants are traveling in a spiral drawing closer to the center.
Let's draw a longitude from the North Pole to our starting point on the Equator. Each time our path crosses that longitude let's say we have travelled one "revolution". Our revolutions will be infinite. However, each revolution will be a shorter distance. I can't find my Calc book, so I'm not sure of the proper way to state this, so I'll use limits.
NOTE: The next part has a lot of guess work.
Let's say for the first revolution we have travelled 1/3 of C. Our next revolution we travel will be 1/3 of 2/3 of C. The next revolution will be 1/3 of the remaining C we have not travelled, and so on. So, if we define a fuction F(x), where x is the number of revolutions, our lim as x approaches infinity would = C. Not exactly sure what the fuction would look like. I feel like what I want is floating up in my head somewhere, but I can't quite access it. F(x) = x/3?? That doesn't seem right. But does anyone see my point.
I'm probably way off, but that's how I see it. It's been about six years since I've taken Calculus and that's what type of problem I think this is.
I wish you had told me that before I wasted 3 hours trying to train these dumb ants.
I really thought this would be more difficult, but it came clear to me this morning.
At this point, I knew that the hypotenuse is the leg*sqrt(2), but you can use a little trig as well, by calculating the sin of the angle. sin(45) = (c/4)/distance travelled, so distance travelled = (c/4)/sin(45). sin(45)=sqrt(2)/2, and you can take it from there.
Quote: CrystalMathTo the North Pole question:
I really thought this would be more difficult, but it came clear to me this morning.
But I am still having a hard time convincing myself that your approach is valid - what is your reason to believe that planar trigonometry can be applied to the sphere in this case?
I was thinking about using a conformal map, like mercator projection, on which the path (loxodrome) would indeed look like a hypotenuse of a right triangle ... but that actually makes it worse, because the distances aren't preserved in general. So, why are they in this case? Coincidence?
Quote: weaselmanI found the answer by straightforward integrating first, and then realized that it is the same as it would be if one traveled on a plane, and found that fact pretty fascinating :)
But I am still having a hard time convincing myself that your approach is valid - what is your reason to believe that planar trigonometry can be applied to the sphere in this case?
I was thinking about using a conformal map, like mercator projection, on which the path (loxodrome) would indeed look like a hypotenuse of a right triangle ... but that actually makes it worse, because the distances aren't preserved in general. So, why are they in this case? Coincidence?
2b: Infinite spirals around the center of the table.
Quote: WizardYou start at any point on the equator and head northwest until you reach the North Pole.
1. What is the distance of your journey? Express your answer as a function of c, where c = the circumference of the earth.
2. How many revolutions around the earth do you make?
I might say that this problem only becomes extremely abstract after a half a turn of the earth. So as an addendum problem what if you go through 1/2 revolution (i.e 180 degree of longitude) following a rhumb line with a constant 45 degree of bearing. What is the distance traveled as a function of c? As a percent of the answer to the original question (i.e. reaching the north pole)? What degree of latitude will you have reached?
The spiraling is a function of any degree of bearing (not just 45 degrees). The 45 on this picture is not the degree of bearing of the rhumb line, but the angle of orientation of the globe for the purposes of visualization.
Quote: CrystalMath
If you consider an infinitesimal step, the curvature of the planet has zero impact. If your step is length ds, and your angle is 45 degrees, then you will get sqrt(2)/2*ds closer to the pole with that step.
For infinitesimal step, yes.
But how do you get from infinitesimal to finite without integration - that's the question.
Quote: weaselmanQuote: CrystalMath
If you consider an infinitesimal step, the curvature of the planet has zero impact. If your step is length ds, and your angle is 45 degrees, then you will get sqrt(2)/2*ds closer to the pole with that step.
For infinitesimal step, yes.
But how do you get from infinitesimal to finite without integration - that's the question.
Could you post your work? My first thought was that it would require integration, but frankly, I didn't know where to start since I haven't used Calculus in 15 years.
Quote: CrystalMath
Could you post your work? My first thought was that it would require integration, but frankly, I didn't know where to start since I haven't used Calculus in 15 years.[/spoiler]
It's pretty straightforward really ...
ds = sqrt(dx^2 + dy^2)
dy = R*d(phi)
dx = dy * tan(a) = dy
where phi is latitude, and a is the azimuth (45 degrees). So:
ds = R*sqrt(2*d(phi)^2) = R*d(phi)*sqrt(2)
Integrate that from 0 to pi/2 to get pi*R*sqrt(2)/2
Quote: weaselmanQuote: CrystalMath
Could you post your work? My first thought was that it would require integration, but frankly, I didn't know where to start since I haven't used Calculus in 15 years.[/spoiler]
It's pretty straightforward really ...
ds = sqrt(dx^2 + dy^2)
dy = R*d(phi)
dx = dy * tan(a) = dy
where phi is latitude, and a is the azimuth (45 degrees). So:
ds = R*sqrt(2*d(phi)^2) = R*d(phi)*sqrt(2)
Integrate that from 0 to pi/2 to get pi*R*sqrt(2)/2
Cool. Makes perfect sense now. Crazy simple integration, I didn't need a calc book for that one. Thanks.
At the risk of waking a sleeping dog, I think that if you can grasp how infinite loops can be made in a finite amount of time you can grasp why .999... = 1.
Quote: WizardThis was an interesting problem. The way I saw it was that while the path was on a sphere at any given moment you can ignore that effect, as if the earth were flat, as CrystalMath explained. That would simply increase the distance by sqrt(2). So my answer is c*sqrt(2)/4 and infinite loops.
At the risk of waking a sleeping dog, I think that if you can grasp how infinite loops can be made in a finite amount of time you can grasp why .999... = 1.
It is a bit difficult, still. I didn't think much of it until the ant problem. The ants will travel
Time for a new problem.
Quote: Wizard... I find it hard to get my mind around the fact that infinite loops can be made in a finite amount of time, but they can. When it comes to infinity, there are lots of such paradoxes.
I suggest that you think of them as an infinite number of loops, almost all of which have almost zero length each. The total length is such that it may be traversed in a modest amount of time. You just might get quite dizzy in the process.
Quote: DocI suggest that you think of them as an infinite number of loops, almost all of which have almost zero length each. The total length is such that it may be traversed in a modest amount of time. You just might get quite dizzy in the process.
I do think of it that way.
Sorry if this has already been said but here was my simple logic.Quote: Wizard...my answer is c*sqrt(2)/4 and infinite loops...
Stop It!!Quote: AyecarumbaSort of like how an infinite string of nines in "0.999999999..." will never reach "1"?