Re: Knowing what you know not about what should be known

[Bob LaMontagne <rlamont@POSTOFFICE.PROVIDENCE.EDU>]

*********** REPLY SEPARATOR  ***********

On 6/20/2004 at 6:11 PM Jeremy Batterson wrote:

I hate to step into this potential hornet's nest (too close
to our past experiences with David Rutherford), but it
turns out that I have tried to come up with a simple answer
to this myself when teaching our conceptual physics type
core course.

My explanation for including both masses has relied on an
argument based on Newton's 3rd law. If the gravitational
forces on the two objects are to be equal and opposite, and
if the mass of one of the objects is to appear in the
formula, then the mass of the other must appear also - and
as a product so the forces will double if either of the
masses doubles.

Is my simple argument naive or misguided? I've always been
uneasy with my approach to this and would appreciate any
criticism offered by the group.

Bob at PC

> We say the the force is the product of masses
>
> divided by the square of the distance between them,
>
> and it is readily understandable why we say the
>
> square of distance, since this is simply the falling
>
> off according to the inverse square. But, why do
>
> we say PRODUCT of masses? What is the physical
>
> cause of that?  If you know about that, I will be very
grateful for your
> reply. Seriously, I have NEVER gotten a real explanation
of this.
> Best wishes,
>
> Jeremy Batterson
>
>
>
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