Re: A Hitchiker's Guide to FORCE.

In sci.physics.relativity, HW@....(Henri Wilson)
<HW@>
wrote
on Mon, 01 Jan 2007 21:40:22 GMT
<1avip25v7b07qkpa1emq7s8qnkmu9btbua@xxxxxxx>:
On Mon, 1 Jan 2007 12:18:29 -0800, The Ghost In The Machine
<ewill@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

In sci.physics.relativity, HW@....(Henri Wilson)
<HW@>
wrote
on Mon, 01 Jan 2007 19:02:20 GMT
<lemip2tjoq07fudfodbc745pqs90ani1n9@xxxxxxx>:
On Mon, 1 Jan 2007 07:53:28 -0800, The Ghost In The Machine
<ewill@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

In sci.physics.relativity, HW@....(Henri Wilson)
<HW@>
wrote
on Mon, 01 Jan 2007 11:35:39 GMT


The rod holds it..

.. and compresses while doing so. That's your other force.


If there were no pull the spring will actually
be at its "natural" length prior to detachment, and
detachment will in that case do absolute nothing.

Ghost the rod is removed. The spring is not detached from the masses.

I am referring to the spring ends being detached from the rod.


If one pushes on a heavy mass that is on an ice floe
or other frictionless surface (assuming one is wearing
cleats or spikes), the mass resists because of its inertia.

That's the crux of it...and the mass 'pushes back' on the instigating
mechanism...How and WHY?

Because you're pushing on it, of course. Newton's Third Law.
It also accelerates.

A LAW isn't a physical process..

True. It is a model thereof.


The spring has the same problem, since it has mass as well.

In this case the mass of the spring is irrelevant Ghost.

Well, unless you have masses on the order of 9.46 * 10^15 kg on each
end, I should say not, if one assumes a one-lightyear-length spring.

irrelevant...

Say what you will, but the spring has mass and in this case the spring
looks to be quite, well, massive.


Is there a force involved? Yes ... yours and the mass's
force on you, as required by Newton's Third. Nothing more,
really.

But where does that force come from?
In true relativistic terms, WHAT IS PUSHING WHAT?

Both are pushing on each other.

If a ball is thrown at a wall, does the ball add momentum to the wall or the
wall move towards the ball and add momentum to IT?


Depends on one's point of view. The ball is thrown,
imparting a slight torque-impulse or momentum-impulse to
the Earth, transmitted through the thrower's feet. (If the
thrower is on an ice floe he might slide backwards.)
Most analyses ignore this point, for hopefully obvious
reasons; after all, the Earth is a ball of its own of mass
5.976 * 10^24 kg -- far larger than most thrown balls.

The ball hits the wall, imparting a reverse torque-impulse
or momentum-impulse to the Earth roughly double the
size of the original impulse (because the ball now heads
back towards the thrower, roughly speaking). The ball
compresses, then expands; the wall also compresses and
expands (for most walls, however, the compression is far
less than that of the ball).

If the ball is properly thrown and the catcher ready,
the catcher can then catch the ball, imparting another
torque-impulse or momentum-impulse to the Earth.
Apart from a little heat to the air, ball, wall, and/or
the thrower's arm, everything more or less balances out.

Some obvious modifications, of course, are as follows.

[1] The ball might be made out of delicate glass, which, if
thrown hard enough, will shatter as it hits the wall
instead of deforming.

[2] The wall might hang from a (larger) wall using a thread
or rope. In this case, the ball will impart momentum
to the wall, causing it to swing.

[3] The ball might *penetrate* the wall if the wall were
made out of, say, thin tissue paper. If the wall is
actually window glass it might either penetrate it
(leaving a ball-sized hole), or shatter the entire
wall.

[4] The catcher might miss the catch and have to go chasing
after the bouncing ball. :-) In this case, the
ball might be doing rather complicated things, like
converting its impulse to rotation and/or experiencing
friction, both against the air and the ground.

Ghost, I am learning a lot about you through your messages.
I can even imagine the house you live in.....completely filled with unnecessary
objects, just like your messages.
....maybe a tractor wheel in your bedroom...or a polar bear trap in the
kitchen. Does it include an obstacle course to make life difficult?


You must be the sort who keeps things so *** and span people can't see
their feet because the floor gleams with the floodlights. :-P

(And then they slip :-P.)

Now shall we get back to the problem at hand? Near as I recall, it's
something along the following lines:

A massless spring 1 light-year long, with very large
weights on each end, is connected to a sufficiently
rigid rod also 1 light-year long. At time zero the
spring+weight ends are detached from the rod (which
more or less is pushed out of the way), and the spring
starts to exert force on the weights. Since the spring
obviously doesn't snap back to its "natural length"
immediately, what force is keeping the spring extended?

--
#191, ewill3@xxxxxxxxxxxxx
Useless C++ Programming Idea #12398234:
void f(char *p) {char *q = strdup(p); strcpy(p,q);}

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