Of course this is wrong. But shooting the cannon north south is quite
different - the effect is tiny ...
J.W.
Am 03.03.20 um 16:23 schrieb H LV:
At the time of Galileo it was argued the Earth could not be spinning
because this motion would result in an observable effect on the
trajectory falling bodies. For example if the Earth were turning
eastward at hundreds of miles per hour then a cannon ball dropped from
a tower would not fall vertically but would hit the ground west of the
tower. In otherwords the ball would not be able to keep up with the
motion of the Earth. To counter this argument Galileo formulated a
thought involving a ship in his Dialogue Concerning the Two Chief
World Systems :
<<Shut yourself up with some friend in the main cabin below decks on
some large ship, and have with you there some flies, butterflies, and
other small flying animals. Have a large bowl of water with some fish
in it; hang up a bottle that empties drop by drop into a wide vessel
beneath it. With the ship standing still, observe carefully how the
little animals fly with equal speed to all sides of the cabin. The
fish swim indifferently in all directions; the drops fall into the
vessel beneath; and, in throwing something to your friend, you need
throw it no more strongly in one direction than another, the distances
being equal; jumping with your feet together, you pass equal spaces in
every direction. When you have observed all these things carefully
(though doubtless when the ship is standing still everything must
happen in this way), have the ship proceed with any speed you like, so
long as the motion is uniform and not fluctuating this way and that.
You will discover not the least change in all the effects named, nor
could you tell from any of them whether the ship was moving or
standing still. In jumping, you will pass on the floor the same spaces
as before, nor will you make larger jumps toward the stern than toward
the prow even though the ship is moving quite rapidly, despite the
fact that during the time that you are in the air the floor under you
will be going in a direction opposite to your jump. In throwing
something to your companion, you will need no more force to get it to
him whether he is in the direction of the bow or the stern, with
yourself situated opposite. The droplets will fall as before into the
vessel beneath without dropping toward the stern, although while the
drops are in the air the ship runs many spans. The fish in their water
will swim toward the front of their bowl with no more effort than
toward the back, and will go with equal ease to bait placed anywhere
around the edges of the bowl. Finally the butterflies and flies will
continue their flights indifferently toward every side, nor will it
ever happen that they are concentrated toward the stern, as if tired
out from keeping up with the course of the ship, from which they will
have been separated during long intervals by keeping themselves in the
air. And if smoke is made by burning some incense, it will be seen
going up in the form of a little cloud, remaining still and moving no
more toward one side than the other. The cause of all these
correspondences of effects is the fact that the ship's motion is
common to all the things contained in it, and to the air also. That is
why I said you should be below decks; for if this took place above in
the open air, which would not follow the course of the ship, more or
less noticeable differences would be seen in some of the effects noted.>>
This is a good argument that a spinning Earth won't result in falling
bodies being left behind but should it also be enshrined as a
fundamentally true principle of motion?
Harry
On Mon, Mar 2, 2020 at 10:24 PM H LV <[email protected]
<mailto:[email protected]>> wrote:
On Mon, Mar 2, 2020 at 9:59 AM Vibrator ! <[email protected]
<mailto:[email protected]>> wrote:
The answer is N3 - and the same reason crashing a car into a
concrete wall is twice as severe as a head-on collision of
equal relative velocity, since it's the vehicles' speeds
relative to the ground that enumerates and underwrites the
value of 'velocity' in the KE equation, not their speed
relative to one another.
In terms of an anticipated collision doesn`t matter if the car is
considered stationary or if the wall along with the Earth - on
which the wall is built - is considered moving. How the car is
affected by the collision will depend on the structural
characteristics of both the car and the wall and how well the wall
is connected to the ground.
The issue I am raising is that Galilean relativity is underwritten
by a conception of motion as something which involves the
anticipation of a collision. The development of motion concepts
like inertia and momentum were inspired by this philosophical view
of motion so whenever they are employed they will always affirm
relativity.
Harry
In short, KE is relative, because motion is relative.. but
what is that motion relative to? The zero-momentum frame;
that is, the FoR from which the net change in momentum in each
direction is equal and opposite.
The bottom line is that when you accelerate towards or away
from the tree, you cause an equal opposite
counter-acceleration of the tree-plus-planet,the net mass of
which divided by your momentum change gives the infinitesimal
but non-trivial counter acceleration of the tree + planet...
hence an external observer sees that the net system momentum
is constant, and correctly calculates that your motion has
virtually all of the kinetic energy of this particular
inertial interaction.
The property of matter enforcing N3 (and thus, N1) is mass
constancy - 1 kg is always 1 kg, regardless of when, or at
what speed, it is measured. More specifically, it is the
time-invariance of inertia, since this is what we're really
dealing with in all the equations of motion and mechanical energy.
Doesn't necessarily apply to time-asymmetric gravitational
interactions tho (ie. the kiiking principle), wherein momentum
can be gained or lost to the inbound vs outboud gravity * time
delta..
Harry
On Wed, Feb 26, 2020 at 7:21 PM H LV <[email protected]
<mailto:[email protected]>> wrote:
In Galilean relativity if I walk eastward towards a tree
with uniform velocity this is equivalent to saying the
tree is moving westward towards me with the same uniform
velocity. As a fundamental proposition of modern physics
this is eminently useful but it is also absurd. It is
useful if what is deemed important about the motion of
bodies is the possibility of past or future collisions (In
the absence of such obvious possibilities the notion of a
force was devised to explain changes in uniform velocity).
It is absurd because it is detached from what we actually
know about the world on a personal level. The tree is at
rest because it is rooted in the Earth and I am moving
towards it. I cannot get the tree and the Earth to move
towards me by simply declaring I am at rest. There has to
be a property of matter that expresses this non-relative
quality of "rootedness" which has been ignored by physics
since the 1600's.
Harry
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