Introduction to Geometric Proportionality
This App features a series of games about geometric proportionality. The figure below shows a circle with an arc and the same curves unwrapped into lines. The points are located proportionally along their respective parents (the full line segment and the circle). Points B and G (in green) are located proportionally at t, while points C and F are at -t.
The lengths of the line segment and arc connecting these points are displayed below; notice that they are identical. Drag the slider and press the "Animate" button to see what happens when the value of t changes.