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Re: Friction

I wrote:
>> Example: A boat. The static friction between the surface of the hull and
>> the surface of the water is zero. At any nonzero velocity, the dynamic
>> friction is greater than zero.

At 09:30 AM 10/18/00 -0500, Doug Craigen wrote:

Example: A block on flat ground with no horizontal forces applied. The
static friction between the surface of the block and the surface of the
plane is zero. At any nonzero velocity, the dynamic friction is greater
than zero.

Is there a problem with this statement?

The problem is that it is non-responsive to the original question, which
asked about the _coefficient_.
-- The block has zero friction in response to zero sideways force; if we
try to calculate the coefficient we get 0/0, which is not very informative.
-- In contrast, the boat has zero static friction even in the presence of
a sideways force; from this we calculate with confidence that the
coefficient is zero, which is what the original question was asking about.