Hi,
the object should (only) be turned by colliding with another object falling from top. The position remains. Only the angle should be changed.
Thanks for your help.
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Create another object (let's call it "Base"), and make it immovable. Create a revolute joint between your object and the Base. Your object should rotate around this joint.
Check out this demo:
howtoconstructdemos.com/seesaw-in-a-platformer-game