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rigid body kinematics

Extinct Kangaroos Couldn't Hop

Another couple of interesting articles to share. Using some "mechanics" principles, researchers have reasoned that 100,000 years ago, kangaroos were too heavy to hop.

A while ago, a different group of researchers published the results of computer modelling (using genetic algorithms) that showed dinosaurs might have hopped and skipped as forms of locomotion! (But only if particularly happy?)

These articles might be good to share with undergraduate engineers for discussion in tutorials. There are issues to discuss with assumptions in both cases. 

What is axis of pure rotation?

   The concept of axis of of pure rotation  ( or instantatious center of rotation)  is a bit confusing. The text books in engineering mechanics( Irvin shames , Beer & Johnston etc) tells that the locus of points in a body, which is (are) having zero veloity.   This fits  well in case of a 2D motion. As a limiting case of this we are assuming the center of rotation is at inifinity for a rigid body moving in a straight line

Instantaneous centre of rotation

Classic undergraduate textboooks on rigid body kinematics (e.g. Hibbeler, Beer & Johnston, etc) point to a quite simple way to locate the instantaneous centre of rotation (ICR) for plane motion of rigid bodies. It came to my mind the idea of using the centre of the osculating circle to any particle belonging to the rigid body as a means to identify the ICR for a 3D motion. Further, I'm thinking about exploring if whether an ICR of zero acceleration can also be located this way. Does anybody know if there's been an attemtp at this idea?

Thanks for your help with this one

Instantaneous centre of rotation

Hi everybody! I'm glad to join iMechanica, just hope to contribute something of interest...and share our penchant for this fascinating subject with all of you

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