Calculating Surface and Volume Integrals on a Sphere: A Problem-Based Approach

In summary, the conversation discussed finding the surface integral of a vector r over a surface of a sphere with a radius and center at the origin. It was also mentioned to find the volume integral of the Gradient•R and compare the results. The speaker suggested integrating r with unit normal vector and using R = r r^r for simplicity. It was also noted that the first part of the problem does not require an integral.
  • #1
Noone1982
83
0
"Find the surface integral of r over a surface of a sphere of radius and center at the origin. Also find the volume integral of Gradient•R and compare your results"


Do I just integrate r to get (1/2)r^2 and plug some limits in since the r-hats equal one?
 
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  • #2
Noone1982 said:
"Find the surface integral of r over a surface of a sphere of radius and center at the origin. Also find the volume integral of Gradient•R and compare your results"


Do I just integrate r to get (1/2)r^2 and plug some limits in since the r-hats equal one?

Well, it must give you what the vector r is right?

[tex]\iint\limits_{S}\mathbf{F}dS[/tex]

where S is the surface area of the sphere and F=r.
 
  • #3
In xyz, r would equal R = x x^ + y y^ + z z^ but I'm just using R = r r^r to be simpler.
 
  • #4
Be sure to distinguish the VECTOR r from the variable r. The vector r is the vector from the origin to the point on the sphere (of radius R?). You will actually be integrating that with the unit normal vector. Since the unit normal vector to the surface of the sphere and r are in the same direction, that is just the length of r. Hmmm, for the first part of this problem you don't actually have to do an integral at all!
 

What is a surface integral?

A surface integral is a mathematical concept used in calculus to calculate the amount of a function over a given surface. It is similar to a regular integral, but instead of integrating over a one-dimensional curve, it integrates over a two-dimensional surface.

How do you set up a surface integral?

To set up a surface integral, you first need to define the surface in terms of a parametric equation or as a graph of a function. Then, you can use a double integral to integrate the function over the surface.

What are the applications of surface integrals?

Surface integrals have various applications in physics, engineering, and other fields. They are used to calculate the flux of a vector field through a surface, the surface area of a curved object, and the work done by a force on a surface.

What is the difference between a surface integral and a line integral?

The main difference between a surface integral and a line integral is the dimensionality of the object being integrated over. A line integral integrates over a one-dimensional curve, while a surface integral integrates over a two-dimensional surface.

How do you evaluate a surface integral?

Evaluating a surface integral involves finding the limits of integration for both the inner and outer integral and then solving the integral using techniques such as u-substitution or integration by parts. It is important to carefully set up the integral and use the correct limits for an accurate evaluation.

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