Calculus of Variation - Shortest path on the surface of a sphere

In summary, the shortest path on the surface of a sphere is a great circle, which is the intersection of a plane through the center of the sphere with its surface. This shorter arc of the great circle is the shortest possible distance between two points on the sphere. The solution is presented as an equation of a plane because it is first derived in terms of angular coordinates on the surface of the sphere, and then translated into an equation of a plane through the center.
  • #1
cxcxcx0505
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Refer to "2.jpg", it said that the shortest path on the surface of a sphere is Ay-Bx=z , which is a plane passing through the center of the sphere. I cannot really understand about this. Does it mean that the shortest path is a ring that connects two points with its center at the center of the sphere?
 

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  • #2
It actually says the geodesic is the intersection of a plane through the center with the spherical surface. This is a great circle, as it says.
 
  • #3
Am I right to say that the intersection of a plane through the center of a sphere is a ring(circle), and the short arc of this ring(circle) which pass through the two points is the shortest path?
 
  • #4
cxcxcx0505 said:
Am I right to say that the intersection of a plane through the center of a sphere is a ring(circle), and the short arc of this ring(circle) which pass through the two points is the shortest path?

The intersection of a plane through the center of a sphere with its surface, embedded in a higher dimensional space (as the reference you cite presents it), is a ring - a great circle. So yes, you are essentially right. Also, you are correct that the shorter arc is the shortest possible distance.
 
  • #5
Thanks PAllen.
 
  • #6
I have another question, why the solution comes out is an equation of a plane and not an equation of a ring(circle)?
 
  • #7
cxcxcx0505 said:
I have another question, why the solution comes out is an equation of a plane and not an equation of a ring(circle)?

They first get the great circle solution purely in terms of two angular coordinates on the sphere's surface. Then they derive that it is the intersection of plane through the center with the sphere.
 
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  • #8
Okie, I get it, many thanks for explaining.
 

Related to Calculus of Variation - Shortest path on the surface of a sphere

What is the calculus of variation?

The calculus of variation is a mathematical theory that deals with finding the optimal curves or surfaces that minimize certain quantities, such as distance or area. It is used to solve many optimization problems in various fields, including physics, engineering, and economics.

What is the shortest path on the surface of a sphere?

The shortest path on the surface of a sphere is known as a geodesic. This is the path that follows the curvature of the sphere and has the shortest distance between two points. It is similar to a straight line on a flat plane, but takes into account the curvature of the sphere.

How is the shortest path on the surface of a sphere calculated using calculus of variation?

To find the shortest path on the surface of a sphere using calculus of variation, we use a functional known as the arc length or path length functional. This functional measures the length of a curve on the surface of the sphere between two fixed points. By minimizing this functional using the calculus of variation, we can find the geodesic or shortest path between the two points on the sphere.

What are the applications of the shortest path on the surface of a sphere?

The shortest path on the surface of a sphere has many practical applications, such as navigation on the Earth's surface, designing flight paths for airplanes, and determining the shortest distance between two points on a globe. It is also used in fields such as computer graphics, where it is used to create 3D models of spherical objects.

What are the limitations of using calculus of variation to find the shortest path on the surface of a sphere?

While calculus of variation is a powerful tool for finding the shortest path on the surface of a sphere, it does have some limitations. It assumes that the surface is smooth and continuous, which may not always be the case in real-life situations. It also relies on certain boundary conditions, such as fixed starting and ending points, which may not always be present in practical applications.

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