Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Elastic collision rule



I cover it because it is an easy to remember rule and it is in their
textbook (Serway and Faughn), however I am uneasy with it because I
don't encourage mass formula memorization and it sounds a lot like
"conservation of velocity" (i.e. the very reason it is so easy to
remember encourages faulty physical thinking). I derive it by solving
the conservation of kinetic energy equation simultaneously with the
conservation of momentum equation.

Lemmerhirt, Fred wrote:

On an exam last Friday, one of my students solved a one-dimensional elastic
collision problem by setting the sum of initial and final velocities of one
particle equal to the sum of the initial and final velocities of the other
particle (and using this in addition to conservation of momentum). I have
not seen this approach before, and am wondering if it is a commonly taught
method. It is, of course, just a rearrangement of the more familiar (to me,
at least) rule that the relative rate of separation of the particles equals
their relative rate of approach. Do any of you teach collisions using this
student's method, or have you seen it presented in a textbook? (I'm
especially wondering if it might be a method that is common in high school
classes.)
______________________________________________________
Fred Lemmerhirt
flemmerhirt@mail.wcc.cc.il.us
http://chat.wcc.cc.il.us/~flemmerh/physics.html
Waubonsee Community College Sugar Grove, Illinois

--

()-()-()-()-()-()-()-()-()-()-()-()-()-()-()-()

Doug Craigen
Latest Project - the Physics E-source
http://www.dctech.com/physics/