>>it is important to distinguish:
>> Equation
>> Causation
>> Definition
>> Calculation
Connie Tyree wrote:
Can you provide some counterexamples?
Causation:
a) I direct my assistant to connect a spring to the object
and elongate the spring a certain amount. Some choose to
interpret this as "causing" a force to be applied. Since
I don't know the mass, I don't know the acceleration
until afterward.
b) I direct my assistant to place the object in a centrifuge
and spin it at a certain rate. Some choose to intepret this
as "causing" an acceleration to be applied. Since I don't
know the mass, I don't know the force until afteward.
Definition:
a) The SI unit of force is _define_ in terms of the SI units
of mass, distance, and time. (The mass unit, at the moment,
is based on an artifact stored in Paris.)
b) The PSSC physics text introduced force by defining it in
terms of an artifact, namely a certain rubber O-ring with
a certain amount of elongation.
Calculation:
a) Mass on a spring: I can calulate the acceleration given
the known mass and known force. (The force is known in terms
of the spring constant and elongation.)
b) Centrifuge: I can calculate the force given the known
mass and known acceleration.
b') Gravitational field.
Equation:
All of the above are examples where F equals ma. There are no
counterexamples.
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If that doesn't answer the question, please ask a more specific
question.