Animations for Understanding Relativity

This tool allows you to compare the coordinate systems of two frames as you control their relative velocity. If it's too big when you load it, use your browser to zoom out until you see the slider. On very old browsers, the slider is not supported and you will see a text box instead; enter the velocity you wish the red frame to display. (But the slider is a lot more fun so try a modern browser!) Click on the image to start.