Re: [Phys-l] inertial +- gravitational mass

[Ludwik Kowalski <kowalskil@mail.montclair.edu>]

On Nov 20, 2006, at 1:06 PM, John Denker wrote:

> . . .   It is not news, because as Popper and others have
> pointed out, it  is never possible for science to establish
>  the "truth" of such propositions.
>        We don't /know/ F=ma.         [2]
>        We don't /know/ F=GmM/r^2     [3]
> We can disprove such propositions, but never prove them.
> The highest praise we can give such a proposition is to say it
>  is "good enough for all practical purposes, so far as we know". . . .

Yes, precision and accuracy set limits on validations of ALL scientific 
propositions. Science is not mathematics. What is wrong with the 
following validation of the F=m*a? We have a nearly frictionless object 
on a smooth and rigid horizontal surface. Using a pulley and a string a 
net horizontal force can be applied to the object along the x axis. The 
cart, whose mass is known, accelerates along the x axis and the 
acceleration is measured. The net force is also measured by a very 
light spring (force-meter) between the object and the string. We 
measure F, m and a. Then we discover that F "happens to be" very close 
to m*a. Is it a coincidence? No it is not; we repeat the experiment 
with different F and different m. And we always find the a=F/m. Popper 
would probably agree that this validation is not deficient. That is how 
I used to introduce the F=m*a to students.

Ludwik Kowalski
Let the perfect not be the enemy of the good.