• Background
• Instructions
• Illustration
• Quiz

## Background

You may remember from physics class that all motion is relative. In the case of the airline passenger, everything around her is moving at the same speed. The comfortable chair, the champagne glass, the overhead television projector, the magazines, and the passenger are all moving together at the exact same speed. We may feel the rumbling of the engines and the rumbling in our stomachs when the plane encounters turbulence. But we feel this motion rather than seeing it. Unless you look out the window, you will not perceive motion visually under these circumstances. From physics that which we use to determine what is moving is called our frame of reference. The aiplane, when you look inside the airplane, is your frame of reference.

In this activity, the role of relative motion will be illustred by looking at a wheel. See if you really perceive the actual motion of the outside of a wheel at is physically is.

## Instructions

### Full Screen Mode

To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.

### Illustration Tab

On the Illustration tab, you can start, stop and alter the motion of squares to experience optic flow.

### Settings

Below is a list of the ways that you can alter the illustration. The settings include the following:

Move: Start and stop the motion of the wheel.
Speed of Wheel: change how fast the wheel moves.
Size of Wheel: Change the size of the wheel.
Show Dot: select to show a red dot on the outside of the wheel (default: show).
Show Wheel: select to show the wheel (default: show).
Track Dot: select to create a bread crumb trail to show the last several positions of the dot to illustrate its actual movement.

### Reset

Pressing this button restores the settings to their default values.