Download the 11 sprites and 17 scripts of "4bar1" and open it in Scratch
Project Notes
This project allows the user to explore four bar linkages. The link (r2) defined by points A and B is the driving link, or "crank". The link (r4) defined by points C and D is the "rocker"
Launch the program by clicking the green flag. Then you can drag the points to different places on the screen and click START to animate the linkage.
NOTE: In order for the crank to rotate fully, a linkage must obey Grashof's law. This states that the sum of the shortest and longest link lengths must not be greater than the sum of the remaining two links. This is checked for automatically, and if the law is violated a warning will be displayed. You can still try to run the linkage, but it will probably not look or function correctly. That's OK ... just click STOP and adjust the points again until you have a linkage that meets the law.
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What is four bar linkage???
It's a common mechanism used in machinery. http://en.wikipedia.org/wiki/Four-bar_linkage
Cool!