Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.

Using momentum in 2-D collisions, and the center of mass

In two dimensions, the total vector momentum is still conserved. That means that each component of momentum remains the same before and after the encounter.

  • Hockey puck slides into brick
  • Hockey puck slides into brick (again)


    The center of mass: discrete case

    When several objects collide or a single object explodes, the individual pieces may fly all over the place. However, if one considers all the pieces as a whole, via the total mass and motion of the center of mass, then Newton's Laws are simple and easy to solve again.


    The center of mass: extended case

    What about extended objects? Some of the nice rules you've learned so far in the class, such as

    
    
        " ... in projectile motion, the x-velocity remains 
          constant while the y-velocity changes linearly with
          time.  The trajectory of an object thus traces
          a parabolic curve ...."
    
    

    don't seem to work if you pick any arbitrary part of an extended body. For example, if I toss a baseball bat up into the air, a movie might show this:

    But how can we find the center of mass of an extended object?

    Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.