non-differentiable physics

["John S. Denker" <jsd@MONMOUTH.COM>]

On 04/28/2003 04:52 PM, David Bowman wrote:
> Just because a function is continuous
> is no reason to presume it must be differentiable.
... and gave a mathematical example.


For bonus points, can anybody give an example
from _physics_ ... some physical quantity that
can be expressed as a function of some other
physical quantity, yet is not differentiable
at some point.

I've asked versions of this question before,
but heretofore nobody has taken the bait.  So
here's a huuuuge hint:  if you had figured this
out in the 1960s you could have gotten (later)
an all-expense-paid trip to Stockholm.