Stokes' theorem and unit vector

In summary: That's what I said in my previous post.No! You can't use Stokes theorem on a scalar. Use it on the vector F=(1,0,0)=1*i+0*j+0*k. That's what I said in my previous post.In summary, the conversation discusses the use of Stokes' theorem to prove that the integral of a unit tangent vector over a closed curve is equal to zero. The conversation includes a discussion of notation and the application of Stokes' theorem to different vector fields. It is determined that using the vector field F=(1,0,0) is the best approach for solving the problem.
  • #1
Sami Lakka
11
0

Homework Statement


Use Stokes' theorem to show that

[tex]\oint\ \hat{t}*ds = 0[/tex]

Integration is done closed curve C and [tex]\hat{t}[/tex] is a unit tangent vector to the curve C

Homework Equations


Stokes' theorem

[tex]\oint F* \hat{t}*ds = \int\int \hat{n}*curl(F)*ds[/tex]

The Attempt at a Solution



Ok, this is really teasing me because I know that is probably simple. Could someone help please?
 
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  • #2
Your notation is pretty sloppy. If t=(tx,ty,tz) the result of your first integral is the vector whose first coordinate is the integral of tx*ds, second is integral ty*ds, and third integral tz*ds. You want to show all of those are zero. Apply Stokes to the constant vector field F=(1,0,0). What does that tell you? What other vector fields would be good to use?
 
  • #3
Dick said:
Your notation is pretty sloppy. If t=(tx,ty,tz) the result of your first integral is the vector whose first coordinate is the integral of tx*ds, second is integral ty*ds, and third integral tz*ds. You want to show all of those are zero. Apply Stokes to the constant vector field F=(1,0,0). What does that tell you? What other vector fields would be good to use?

Yes, sorry about the notation, it is direct copy from the book that I'm studying. t is a unit vector with components (dx/ds, dy/ds, dz/ds) so after the multiplication the integral is taken from vector (dx, dy, dz)
 
  • #4
Sami Lakka said:
Yes, sorry about the notation, it is direct copy from the book that I'm studying. t is a unit vector with components (dx/ds, dy/ds, dz/ds) so after the multiplication the integral is taken from vector (dx, dy, dz)

Ok, now I think I got it. I should use Stokes' theorem with F=1 (scalar). What bothered me was that I was all the time looking at the cross product in curl which is not defined for scalars. Of course the cross product is only a notation, not actual vector cross product.
 
  • #5
Sami Lakka said:
Ok, now I think I got it. I should use Stokes' theorem with F=1 (scalar). What bothered me was that I was all the time looking at the cross product in curl which is not defined for scalars. Of course the cross product is only a notation, not actual vector cross product.

No! You can't use Stokes theorem on a scalar. Use it on the vector F=(1,0,0)=1*i+0*j+0*k.
 

FAQ: Stokes' theorem and unit vector

What is Stokes' theorem?

Stokes' theorem is a mathematical theorem that relates the surface integral of a vector field over a closed surface to the line integral of the same vector field around the boundary of the surface. It is also known as the generalized Stokes' theorem or the Kelvin-Stokes theorem.

What is a unit vector?

A unit vector is a vector with a magnitude of 1, often used to indicate a direction in space. It is typically represented by a lowercase letter with a caret (^) symbol above it, such as ̂v.

How is Stokes' theorem related to unit vectors?

In Stokes' theorem, the surface and line integrals involve the dot product of the vector field with the unit normal vector to the surface or the unit tangent vector to the curve. This allows for the calculation of the flux or circulation of the vector field in a specific direction.

What is the significance of Stokes' theorem in science?

Stokes' theorem is a fundamental tool in vector calculus and is used in many areas of science and engineering, including fluid mechanics, electromagnetism, and differential geometry. It allows for the simplification of complicated surface and line integrals and helps in solving problems related to flux and circulation of vector fields.

Can Stokes' theorem be applied in both two and three dimensions?

Yes, Stokes' theorem can be applied in both two and three dimensions. In two dimensions, it is known as the Green's theorem, and in three dimensions, it is known as the Kelvin-Stokes theorem. However, the underlying principles and equations remain the same in both cases.

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