I restate Justin's question below with updated text reference.
At 09:32 10/7/00 -0400 and 10:32 10/6/00 -0400, Justin Parke wrote:
In my AP physics class we were recently discussing the drag force and how
it applies to Newton's second law [please no comments on the validity of
Newton's law or inertial reference frames! :) ].
In any case, an example I pulled from Classical Dynamics (3rd ed., Marion
and Thornton) had a resistive force proportional to mv. The Drag force
given by Halliday and Resnick, however, does not depend on the mass of the
object in question at all. My question is: is the resistive force in the
Marion & Thornton problem an accurate picture of reality or simply made up
to simplify the math? It doesn't seem reasonable to me that the resistive
force would depend on the mass...otherwise no one would think that heavy
objects fall faster!
Justin Parke
Oakland Mills High School
The drag proportional to velocity term reminds me of the conventional
oil filled dash pot attached to the ball on a spring - an embodiment
of damped oscillatory motion. The mass is more problematical.
Dropping a feather and a steel ball in air shows that the heavy
object drops faster.
Though I don't have the context in which the problem was posed -
I should stress that engineers are faced every day with shaping laws
of motion to suit the purpose at hand.
An example of shaping resistance to depend on mass: we want elevators
to move along at the same rate - heavy or light.
brian whatcott <inet@intellisys.net> Altus OK
Eureka!