This is a demonstration of a mechanical linkage invented by James Watt. In Watt's linkage there are two long but equal length rods connected by a short rod. The midpoint of the short rod is constrained to move in an approximation of a straight line (but actually a figure eight). My version allows arbitrary lengths for the three rods. See http://en.wikipedia.org/wiki/Watt's_linkage for more information.
Instructions: Click and drag the point B to see how the linkage moves. Click the Trace checkbox to show the path followed by the midpoint of the orange rod. Drag the slider bars to change the lengths of the rods. The points A and C can also be moved. What shapes can you create?
Instructions: Click and drag the point B to see how the linkage moves. Click the Trace checkbox to show the path followed by the midpoint of the orange rod. Drag the slider bars to change the lengths of the rods. The points A and C can also be moved. What shapes can you create?
Another implementation of Watt's linkage in GeoGebra is here:
http://web.mat.bham.ac.uk/C.J.Sangwin/howroundcom/straightline/Watt1.html
Download this worksheet: