MAM2000 (Dimension/Demos)

# Rotating 3-Space

 You will need to enable Java in order to use this demonstration.

Please be patient while the applet is loaded (60K)...

## Interaction Controls

Dragging the mouse will rotate three-space around an axis within the plane of the screen.

Dragging with the middle mouse button, or while the `Option` or `Alt` key is held down, rotates space about an axis perpendicular to the screen.

The readout at the bottom represents the rotation matrix for the coordinate axes (see below). Because the 3D to 2D projection is orthographic rather than in perspective, it is sometimes hard to tell what is in front and what is behind (far away things do not get smaller). Look at the colors at the overcrossings to get your orientation back if you get confused.

When you are done with the demonstration, click on the up button at the top of this page, or use your browser's back button to go back to the previous page.

This demonstration is one of a series: you can view the 2D version, or move on to the 4D version next.

## What this Demonstrates:

Dragging the mouse will cause the axes in two-space to rotate. The first column of the array at the bottom of the picture keeps track of the three new coordinates of the unit vector that points along the x axis. Similarly the second and third columns represent the new positions of the unit vectors along the y and z axes.

You can add the squares of the components in each column to see that the length of either coordinate vector remains the same, i.e. equal to one, throughout the rotation.

Also, for those familiar with the dot product, it is possible to check that the columns of this array, or matrix as it is known, are perpendicular throughout. Any matrix whose columns form mutually perpendicular vectors is called an orthogonal matrix.

Once we know the positions of the three axes, we can apply the same rotation to any figure at all. In this case, we rotate a cube along with the axes. This is the basis of the rotations that show up in computer animation, and in other applications in 3D computer graphics.

 Math Awareness Month 2000 Last modified: Jun 10, 2000 10:40:28 AM Comments to: `thomas_banchoff@brown.edu` Hosted by: The Math Forum