[Phys-L] Re: A problem of motion and derivatives

[Leigh Palmer <palmer@SFU.CA>]

Recall the problem posed earlier in this group, that of braking a
moving automobile smoothly to a stop? Turns out it couldn't be done,
and one reason is that the car is suspended. It is, in essence, two
masses [(car body) and (wheels and axles)] connected by a spring, and
the braking force is only applied to one of the masses. The problem
Al refers to here, and that we see often in false relativistic
paradoxes, is that there is no such thing as a rigid body. It does
bear repeating.

Leigh

On 7-Nov-05 Al Bachman wrote:

> The situation is actually more complex in that there is also no
> such thing
> as a rigid body! This means that an applied force has to propagate
> through
> objects as a compressional wave (speed of sound ?) before a steady
> state
> is obtained. The bottom line is that you can't expect the simple
> behavior
> we describe in elementary problems to withstand scrutiny in the
> limit of
>  t -> 0 .
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