Re: Cause and Effect

[John Denker <jsd@MONMOUTH.COM>]

At 12:39 PM 10/23/00 +0530, D.V.N.Sarma wrote:

> As far as Newton's laws are concerned the situation is
>
> No force --------------> No acceleration
> There is force---------> There is acceleration
>
> This is a characteristic of  a casual relationship.

But one can equally well write

        No acceleration---------> No force
        There is acceleration---> There is force

which is characteristic of a causal relationship in the other direction.

The laws of motion do not favor one direction of causation over the other.


> The concept of force mainly arises from the subjective experience
> of pushes and pulls.
>
> The awareness of acceleration is not subjective.

Force is measurable.
Acceleration is measurable.
I don't consider one more subjective than the other.
Until this moment it never occurred to me that anyone would consider one
more subjective than the other.
There is nothing in the laws of physics that bestows preferred status on
one or the other.

This approach leads to innumerable other questions:
        Is energy more subjective than force?
        Is momentum more subjective than temperature?
        Is luminous intensity more subjective than distance?
I think all such questions are irrelevant.  If it's measurable, it's
measurable, and that's all there is to it.

> Therefore since we have to proceed from known to the unknown,
> force causes acceleration is only thing that is understandable and
> not vice versa.

We can know force without acceleration, by observing the extension of a
calibrated spring.  This is the usual starting point for a pedagogical
operational definition of force.  There is nothing subjective about it.

Is it common to tell students that force must be understood in terms of
acceleration?  I wasn't taught that way, and until this moment it never
occurred to me that anyone might teach that.

Also note that the direction mentioned above (from allegedly more known
acceleration to allegedly less known force) suggests that acceleration
comes before force, i.e. that acceleration causes force, which is
diametrically
opposite to the point that was being advocated.