Re: Relativists Conclusively Prove They Are a Bunch of Morons


"Daryl McCullough" <stevendaryl3016@xxxxxxxxx> wrote in message
news:em8qar08t8@xxxxxxxxxxxxxxxxxx
Pax says...

"Daryl McCullough" <stevendaryl3016@xxxxxxxxx> wrote

Okay, consider a ball connected to a string that is connected to a
vertical rotating pole whose center is fixed in the ground. The forces
at
work are (ignoring gravity):

1. The string exerts an inward force on the ball. (centripetal force)
2. The ball exerts an outward force on the string. (reaction to
centripetal)

That's centrifugal

Yes, it is sometimes called "centrifugal force", but it's
not the force in contention. When some physicists say that
the centrifugal force is fictitious, they are *not* talking
about force 2, they are talking about force 5 below.

the real force which is a result of inertia, determined
by momentum, which imparts inertial energy. It's not a reaction to
centripetal

Yes, it certainly is. The string pulls on the ball, and the ball
pulls back on the string. Equal and opposite forces.

If you *don't* mean the reaction to the centripetal force,
then you don't mean my force 2.

the circular path of the ball is a reaction to centripetal, the
fact the ball is flying out in the air, as opposed to dangling from the
string, is the result of centrifugal force. Centripetal force can't throw
that ball out in mid-air to the end of the stretched-out string, only
centrifugal force can do that.

You're talking about force 5 below. You're talking about a force
on the *ball*. But my force 2 is a force on the *string*. That's
the whole point of my list, to get straight which forces we are
talking about.

3. The string exerts an outward force on the pole.

Why?

If you pull on a string, the string pulls back on you.
That's Newton's equal and opposite forces at work.

4. The pole exerts an inward force on the string.

These 4 forces are all real, and they exist in every reference frame,
inertial or not. However, in the rotating reference frame of the pole,
it
is sometimes common to introduce a fictitious fifth force:

5. The ball experiences an outward force due to rotation (centrifugal
force)

That is not a fictitious force.

It is, in the sense that it is a force that vanishes when you
describe motion in an inertial Cartesian coordinate system.
Real forces are independent of coordinates, in the sense that
if they are nonzero in one coordinate system, then they are
nonzero in *every* coordinate system.

The outward force on the ball (Force 5) exactly balances the inward
force
on the ball (force 1).

Not always, depends on the strength of the string.

Right. In the case in which the ball is at rest in the noninertial
coordinate system, forces 5 and 1 are in balance.

Of the 5 forces mentioned,

Force 1 (inward force on the ball) and force 2 (outward force on the
string) are *always* equal and opposite.
Force 3 (outward force on the pole) and force 4 (inward force on the
string) are *always* equal and opposite.
Force 1 and Force 5 ("centrifugal force") are only equal and opposite
if the ball is at "rest" in the rotating coordinate system.

Note that although force 5 is equal to force 2 in magnitude and
direction,
they are *not* the same force, because force 5 is a force on the *ball*,
while force 2 is a force on the *string*. To see that force 2 and force
5
are not the same, consider the case in which the string is *elastic*;
that
is, the string is allowed to stretch. In that case, Force 5 will be
*greater* than force 2.

I disagree 2 and 5 are the same force.

No, they're not. Force 2 is the force on the *string*, while
force 5 is a force on the *ball*. They are not the same force,
and they are not equal in magnitude (except in the case in which
the ball is at rest in the rotating coordinate system).

If the string were elastic, the weight of the ball combined with
the weight of the string would allow the ball to move farther
outward, all due to the exact same force, inertia.

Once again, keep straight what are the forces on each object.
The forces on the *ball* in the rotating system consists of:
Force 5: The centrifugal force pulling outward on the ball.
Force 1: The centripetal force pulling inward on the ball.
These two forces, as you have pointed out, do not have to
be equal. If Force 5 is greater than Force 1, the ball will
move outward. If Force 1 is greater than Force 5, the ball
will move inward.

The forces on the string consists of:
Force 2: The outward force of the ball on the string.
Force 4: The inward force of the pole on the string.

Force 2 is *always* equal in magnitude to Force 1.
Force 5 is sometimes unequal in magnitude to force 1.
Therefore, Force 5 is sometimes unequal in magnitude
to force 2.

Take the ball off the string.

Daryl McCullough
Ithaca, NY

Be well - Pax


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