Problem 59 - Advanced Engineering Mathematics

Question

In Problems \(59-62\), convert the point given in spherical coordinates to (a) rectangular coordinates and (b) cylindrical coordinates. $$ \left(\frac{2}{3}, \frac{\pi}{2}, \frac{\pi}{6}\right) $$

Step-by-Step Solution

Answer

Rectangular coordinates: (0, 1/3, √3/3); Cylindrical coordinates: (1/3, π/2, √3/3).

Step 1: Understand Spherical Coordinates

A point in spherical coordinates is represented as \(( ho, \theta, \phi)\), where \(\rho\) is the radius, \(\theta\) is the angle in the xy-plane from the positive x-axis, and \(\phi\) is the angle from the positive z-axis.

Step 2: Convert to Rectangular Coordinates

To convert spherical coordinates \((\rho, \theta, \phi) = \left(\frac{2}{3}, \frac{\pi}{2}, \frac{\pi}{6}\right)\) to rectangular coordinates \((x, y, z)\), we use the formulas:\[x = \rho \sin(\phi) \cos(\theta)\]\[y = \rho \sin(\phi) \sin(\theta)\]\[z = \rho \cos(\phi)\]Plugging in the values, we compute:\[x = \frac{2}{3} \sin\left(\frac{\pi}{6}\right) \cos\left(\frac{\pi}{2}\right) = \frac{2}{3} \times \frac{1}{2} \times 0 = 0\]\[y = \frac{2}{3} \sin\left(\frac{\pi}{6}\right) \sin\left(\frac{\pi}{2}\right) = \frac{2}{3} \times \frac{1}{2} \times 1 = \frac{1}{3}\]\[z = \frac{2}{3} \cos\left(\frac{\pi}{6}\right) = \frac{2}{3} \times \frac{\sqrt{3}}{2} = \frac{2\sqrt{3}}{6} = \frac{\sqrt{3}}{3}\]Thus, the rectangular coordinates are \((0, \frac{1}{3}, \frac{\sqrt{3}}{3})\).

Step 3: Convert to Cylindrical Coordinates

To convert spherical coordinates \((\rho, \theta, \phi) = \left(\frac{2}{3}, \frac{\pi}{2}, \frac{\pi}{6}\right)\) to cylindrical coordinates \((r, \theta, z)\), we use the formulas:\[r = \rho \sin(\phi)\]\[\theta = \theta\]\[z = \rho \cos(\phi)\]Plugging in the values, we compute:\[r = \frac{2}{3} \sin\left(\frac{\pi}{6}\right) = \frac{2}{3} \times \frac{1}{2} = \frac{1}{3}\]\[\theta = \frac{\pi}{2}\]\[z = \frac{\sqrt{3}}{3}\]Thus, the cylindrical coordinates are \((\frac{1}{3}, \frac{\pi}{2}, \frac{\sqrt{3}}{3})\).

Key Concepts

Rectangular Coordinates

Rectangular coordinates, also known as Cartesian coordinates, are used to pinpoint a location in a three-dimensional space using three values:

• \(x\) - the horizontal distance from the origin.
• \(y\) - the vertical distance from the origin.
• \(z\) - the depth from the origin along the third axis.

These coordinates are incredibly useful for visualization and are the go-to system for graphing equations in math and science. The axes involved are mutually perpendicular, creating a 3D grid of cubes. This system is particularly handy when dealing with problems involving direction and distance.
The conversion from spherical to rectangular coordinates is conducted using certain trigonometric formulas:

• \(x = \rho \sin(\phi) \cos(\theta)\)
• \(y = \rho \sin(\phi) \sin(\theta)\)
• \(z = \rho \cos(\phi)\)

These equations involve multiplying the spherical radius \(\rho\) by the sine and cosine of the spherical angles \(\phi\) and \(\theta\). Utilizing these relationships, we can pinpoint the exact location of a point in a 3D rectangular space.

Cylindrical Coordinates

Cylindrical coordinates are another way to describe a location in three dimensions. This system modifies the polar coordinate system to include a height component. Cylindrical coordinates consist of three parts:

• \(r\) - the radial distance from the origin in the xy-plane.
• \(\theta\) - the angular position in the xy-plane, measured from the positive x-axis.
• \(z\) - the height above or below the xy-plane.

In cylindrical coordinates, movement occurs more naturally in a radial direction, and this can simplify calculations where circular symmetry is present. For instance, pipes, towers, and spiral staircases are conveniently described using this system.
Converting from spherical to cylindrical coordinates requires less effort since the \(\theta\) remains the same:

• \(r = \rho \sin(\phi)\)
• \(\theta = \theta\)
• \(z = \rho \cos(\phi)\)

This way, both cylindrical and spherical systems share the angular component, making such transformations smoother than might be expected.

Coordinate Transformation

Coordinate transformation is the process of converting coordinates from one system to another. This transformation helps in solving complex problems by switching to a coordinate system where the computation might be simpler.
Each coordinate system—rectangular, cylindrical, and spherical—serves a unique purpose and provides insights into different aspects of geometry and physics. For instance:

• Rectangular coordinates are optimal for linear measurements and straightforward distance calculations.
• Cylindrical coordinates perfectly fit objects with radial symmetry.
• Spherical coordinates excel with objects that have true spherical symmetry, such as planets or stars.

To perform a coordinate transformation, it is important to understand the relationship between the systems. This involves using formulas like the ones provided above or looking at visual aids showing how points correlate across these coordinate grids. Mastery of these transformations can greatly aid in understanding multi-dimensional spaces and their applications in real-world scenarios such as engineering, aerospace, and mathematical modeling.