Re: Cause and Effect

[brian whatcott <inet@INTELLISYS.NET>]

At 11:39 10/22/00 -0700, Robert wrote:
> ///

> I do not believe the laws or measurements tell us that forces
> > cause accelerations.  Physics doesn't seem to care if forces cause
> > accelerations or visa-versa.

> ///
> Newton told you forces cause accelerations.
> ///
> Leigh


Here is what Newton wrote in Principia:

AXIOMS, OR LAWS OF MOTION
....

Law II
The change of motion is proportional to the motive force impressed; and is
made in the direction of the right line in which that force is impressed.

IF any force generates a motion, a double force will generate double the
motion, a triple force triple the motion, whether that force be impressed
altogether and at once, or gradually and successively. And this motion
(being always directed the same way with the generating force), if the
body moved before is added to or subtracted from the former motion,
according as they directly conspire with or are directly contrary to
 each other; or obliquely joined, when they are oblique, so as to produce
 a new motion compounded from the determination of both.

Law III
......

(Motte's Translation, Cajori's revision)


Law II is transcribed above in total.
Newton's "Motion" is often taken as 'momentum', hence the first sentence
conveys: change of momentum is proportional to force impressed.
d(mv)/dt = F
This is very like the current rendering:
m.dv/dt = F

However the second sentence could then be rendered as
 m.v = F
or
m.v = Int(F).dt

...as far as I can see.
     I don't suppose this was Leigh's intention.

 Newton's word translated as "body" could possibly be rendered as 'mass'.

Sincerely

Brian




brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!