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# Kinematic equations (Was: Crib Sheets)

Rick Tarara <rtarara@saintmarys.edu> wrote:
[...] I HATE books that produce a separate set of kinematics
equations for projectile motion (with y's for the vertical motion and
substituting 'g' for the acceleration). This just reinforces student's
belief that physics is just a bunch of equations to be
memorized--specific equations for each problem. I force students to work
such problems with ONLY the 4 standard kinematics equations--WHICH I
constantly stress are all derived FROM the DEFINITION of acceleration!

I've something like this, but I used just *two* kinematic equations:

x = x0 + v0*t + 0.5*a*t^2
v = v0 + a*t

One constructs a standardized diagram that looks something like this:

start (a = ?) ---> finish
X---------------------------------------X
(t0 = 0) t = ?
x0 = ? x = ?
v0 = ? v = ?

Then one fills in whatever initial quantities are given, and solves the x
and t equations as necessary to get the unknowns. This means re-deriving
the other two "basic kinematic equations" every time one needs them. Of
course, most students prefer to memorize the equations instead.

--
Jon Bell <jtbell@presby.edu> Presbyterian College
Dept. of Physics and Computer Science Clinton, South Carolina USA