Question

Define a parametric surface.

Short answer

A parametric surface in a three-dimensional space is given by \(\vec{r}(u, v) = x(u, v)i + y(u, v)j + z(u, v) k\), where \(x, y,\) and \(z\) are functions of parameters \(u\) and \(v\), and \(i,j,k\) are unit vectors along the x-axis,y-axis, and z-axis respectively. For example, a sphere of radius r can be parameterized as \(\vec{r}(u, v) = r \sin(v) \cos(u)i + r \sin(v) \sin(u)j + r \cos(v)k\).

Step-by-step solution

Understand a Parametric Surface

A parametric surface is defined by a parametric equation with two parameters usually denoted as \(u\) and \(v\). In a three-dimensional space, a parameterized surface can be represented as \(\vec{r}(u, v) = x(u, v)i + y(u, v)j + z(u, v) k\), where \(x, y,\) and \(z\) are functions of parameters \(u\) and \(v\), \(i,j,k\) are unit vectors along the x-axis,y-axis, and z-axis respectively.

Example of a Parametric Surface

As an example, we will define a parametric equation for a sphere of radius r. For a sphere, we can parametrize it using spherical coordinates. So, \(\vec{r}(u, v) = r \sin(v) \cos(u)i + r \sin(v) \sin(u)j + r \cos(v)k\), where \(u\) is the azimuthal angle and varies in the interval \( [0,2\pi]\), \(v\) or \( \theta\) is the polar angle or zenith angle and varies in the interval \([0,\pi]\).

Visualizing the Parametric Surface

In this step, plot the graph for the sphere using the equation from the previous step. This way, you can visualize the defined parametric surface. Remember that it is always a good idea to use a computer software for plotting three-dimensional graphs.

Key concepts

Parametric Equation

Parametric equations are a way to express a mathematical relationship using parameters. Imagine you’re going on a treasure hunt and your map uses the distances traveled north and east from your starting point. Similarly, in mathematics, we can define a curve or surface by specifying how each point moves based on two or more parameters.

In the context of our treasure map, if each step's direction depends on how many steps you've already taken (our parameters), your path would be represented by a parametric equation. Applied to a surface in three-dimensional space, a parametric equation uses two parameters, typically denoted as \(u\) and \(v\), to define the position vector \(\vec{r}(u, v)\) of every point on the surface. This position vector includes functions \(x(u, v)\), \(y(u, v)\), and \(z(u, v)\) which indicate how far along each of the three axes—\(i\), \(j\), and \(k\)—the point is located.

Three-Dimensional Space

Three-dimensional space is like the world around us, having length, width, and height. It's where all physical objects reside, and mathematicians represent it using three axes—usually named the x-axis, y-axis, and z-axis. Each point in this space can be identified by its coordinates along these axes.

In math, when we want to show the location of a point or shape this space, we use a three-coordinate system. The beauty of math allows us to explore this space not just by using simple (x, y, z) coordinates but also through parameters, as in a parametric equation, or even spherical and cylindrical coordinate systems. By learning how to describe locations and shapes in three-dimensional space, students enhance their ability to visualize and solve problems involving complex objects or phenomena.

Spherical Coordinates

Spherical coordinates are a way of representing points in three-dimensional space with angles and distance, similar to how you might describe the location of a star in the night sky. Instead of stating how far left-right and up-down (like in the rectangular coordinates), spherical coordinates express a point's position with a distance from the origin (radius), an angle on the horizontal plane (azimuthal angle \(u\)), and an angle from the vertical axis (polar angle \(v\)).

These coordinates are incredibly useful for objects that are naturally spherical or radial, like planets or sound waves emanating from a point. In the parametric equation of a sphere's surface, \(u\) sweeps around 360 degrees (the azimuthal angle), and \(v\) goes from north to south pole, covering 180 degrees (the polar angle). With this system, you can easily describe the entire surface of a sphere, much like how you'd give directions using landmarks in your neighborhood.