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

We don't teach 'conservation of velocity' but our algebra
(arithmetic) based course DOES treat collisions with the separation
speed = approach speed (or reduced by a 'coefficient of restitution'
for partially elastic cases.).

We do it because the algorithm is simple and powerful. Once they
master relative velocities, it's pretty much clear sailing. We don't
get to KE conservation 'til much later in the semester and it gives
'em a thrill to be able to solve these problems well before the trig
course gets the two humongous equations to 'plug into' to get the
same results.

At 9:24 AM -0600 11/8/99, 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.)

Find out what HS the kid is from and we can all tip our hats to a
creative teacher.

-. .-. .-. .-. .-. .-. .-. .-. .-. .-
\ / \ / \ N / \ C / \ S / \ S / \ M / \ / \ /
`-' `-' `-' `-' `-' `-' `-' `-' `-'
Chuck Britton Education is what is left when
britton@odie.ncssm.edu you have forgotten everything
North Carolina School of Science & Math you learned in school.
(919) 286-3366 x224 Albert Einstein, 1936