Area element in polar coordinates (hard question)

In summary, the differential area element in polar coordinates can be derived using trigonometric identities by considering a small "square" at the end of a vector given by r = (r, θ). The area element is found to be dA = r.dθ.dr, where dθ and dr represent the changes in θ and r, respectively. Alternatively, one can use partial derivatives of x and y in terms of θ and r to find the area element.
  • #1
markapplegate
2
0

Homework Statement



using only trigonometric identities, derive the differential area element in polar coordinates? any help with this problem or at least a start?


Homework Equations



i found this so far
dA=(dr)(rd θ)

The Attempt at a Solution


i have tried to figure this one out but i really have no clue how to start the problem, i tried taking derivatives but got no where , I am not sure how to use a trigonometric identitie in this problem?
 
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  • #2
geomtrically:

say you have a vector given by r = (r, θ)

think of a small "square" at the end of the vector,
one side length is given by moving in the r dierction by dr
the other side is swept by changing θ by dθ, the length is a circular arc so will be r.dθ

so the "square" area elemnt is givne by
dA = r.dθ.dr

algebraically:

you know for cartesian coordinates dA = dx.dy
write x & y in terms of θ & r, then take the partial derivatives to find dx(r,θ)
 
  • #3
thank you, i haven't learned partial derivatives yet, but i will try to figure that out and I am guessing i will be able to use some trig id. after i take the partial derivative.
 

What is an area element in polar coordinates?

The area element in polar coordinates is a mathematical concept used to calculate the area of a small region in a polar coordinate system. It is represented by the symbol dA and is equal to the product of the radial distance and the angular distance.

How is the area element calculated in polar coordinates?

The area element in polar coordinates is calculated by first determining the infinitesimal changes in the radial and angular coordinates, represented by dr and dθ respectively. The area element is then equal to dr * r * dθ, where r is the radial distance and dθ is the angular distance.

Why is the area element in polar coordinates considered a hard question?

The area element in polar coordinates is considered a hard question because it requires a good understanding of polar coordinates and their conversion to rectangular coordinates. It also involves the use of calculus and trigonometry, which can be challenging for some people.

How is the area element used in practical applications?

The area element in polar coordinates is used in various fields of science and engineering, such as physics, astronomy, and fluid mechanics. It is used to calculate the area of irregular shapes, as well as to determine the volume and surface area of objects with curved surfaces.

Can the area element be calculated in other coordinate systems?

Yes, the concept of an area element can be extended to other coordinate systems, such as cylindrical and spherical coordinates. However, the calculation of the area element may be more complex in these systems as they involve more variables and conversion between coordinate systems may be necessary.

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