Re: origin of inertia
From: bz (bz+sp_at_ch100-5.chem.lsu.edu)
Date: 03/28/05
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Date: Mon, 28 Mar 2005 03:54:09 +0000 (UTC)
"JM Albuquerque" <jm.aREM.OVE@sapo.pt> wrote in
news:3ap1rgF6bbci5U1@individual.net:
>
> "bz" <bz+sp@ch100-5.chem.lsu.edu> escreveu na mensagem
> news:Xns96267F072C817WQAHBGMXSZHVspammote@130.39.198.139...
>> "JM Albuquerque" <jm.aREM.OVE@sapo.pt> wrote in news:3ao3j7F6c0u01U1
>> @individual.net:
>>
>> >
>> > "bz" <bz+sp@ch100-5.chem.lsu.edu> escreveu na mensagem
>> > news:Xns9625E11F8F420WQAHBGMXSZHVspammote@130.39.198.139...
>> >> "JM Albuquerque" <jm.aREM.OVE@sapo.pt> wrote in
>> >> news:3amf7iF6coaueU1@individual.net:
>> >>
>> >> >
>> ...
>> >> >> > What do you see accelerating ?
>> >> >>
>>
>> You are confusing force with acceleration. Work is force times
>> distance.
>
> This is a free motion device.
> All the motions are free in a gyro.
> Free like a rock in space.
> To apply force over a free body you need to apply
> acceleration.
> F = ma
A gyro that is free to turn in all directions does not precess if it is
properly constructed and balanced.
>
> Without a force you cannot talk about any work.
Agreed. Force. Not acceleration, force.
>> >> >> I see g attempting to accelerate all the particles in the top.
>> >> >
>> >> > Right.
>> >> > Attempting, but not doing it.
>> >>
>> >> The force is there.
>> >
>> > It is the same situation as above.
>> > The force is there but no work is being done in the vertical
>> > direction (the direction that gravity acts).
>>
>> Zero work is done because W = F d and there is no d.
>
> You have said that precession carries a torque on it.
> I do see "d" (distance) in the precession motion.
> What I don't see is the force.
gravity exerts a force. You know, F = G(m1 m2)/r^2
>
In that the case of my above statement, I was talking about me sitting on
a bed. In that case, no work was done because there was no distance moved.
Gravity exerts a force on me but no work is done because there is no
movement.
>
>> >> > And, because of symmetry, all those centripetal forces
>> >> > cancel out producing zero force on the center of mass.
>> >>
>> >> They would cancel if it were not for gravity.
>> >
>> > I don't understand what you mean.
>> > Can you explain please ?
>>
>> Gravity acts in a non symetrical way on each of the particle. If it
>> were symetrical, the gyro would have no weight.
>
> We were talking about centripetal forces, not gravity.
I said 'they would cancel if it were not for gravity'. I was talking about
gravity. Gravity prevents the centripedal forces from cancelling IF the
gyro is precessing it implies that either the gyro is not fully gimbled or
it is not balanced.
...
>> >>
>> >> wrong. The center of mass of the gyroscope moves from one point to
>> >> another. Force times distance is work.
>> >> Work is done.
>> >
>> > I cannot agree whit that.
>> > The center of mass of the gyroscope moves from one point to
>> > another, but there is no force associated with that motion.
>>
>> There is the force of gravity. Conservation of angular momentum changes
> the
>> direction, just like a pully would do.
>>
>> >
>> > You want to backup the acceleration of gravity, which exists
>> > in the vertical direction, as being translated to the horizontal
>> > plane where the motion occurs. What physical support do
>> > you have to claim that ?
I demonstrated that it can be done with a rope to a pully in the ceiling
in another article.
>>
>> The gyro precesses. Work = force times distance.
>
> What force.
the force of gravity.
> The gyro is free to rotate, so that the only way to apply
> force is by means of inertia = acceleration.
> It is like a free rock in space.
> To apply force over a free body you need to apply
> acceleration.
>
Applying a force results in an acceleration.
> You don't have acceleration in the precession motion.
I never claimed an acceleration. YOU claimed that an acceleration was
needed. I claimed a force. The force of gravity. Force causes the precession.
F x d is work.
>> The center of gravity of the gyro moves a distance. Gravity is the
>> force that moved it that distance. Work is done.
> You are wrong.
on the contrary.
>
> The gyroscopic effect is ruled by the formula below:
> wp = mg r / L
>
> being:
> L - the disk main angular momentum = I w
> mg r - torque due to gravity.
> wp - the precession angular speed.
>
> Did you realize that the precession angular speed depends
> on the main angular momentum.
>
> If you have the disk spinning at very high speed the
> precession angular speed will be very small for the
> same mass.
>
> If you have the disk spinning at low speed the
> precession angular speed will be very fast for the
> same mass.
>
> Did you realize there is minimum speed and below
> that speed the gyroscope won't work anymore ?
>
of course, when you have zero Angular momentum, the gyro is not a gyro
anymore.
> How that relates to your force / torque misunderstanding ?
It doesn't.
>
> Assume the same torque due to gravity (T = mg r).
> If the disk spins at 1000 RPM you have wp = 100 RPM
> If the disk spins at 10000 RPM you have wp = 10 RPM
>
> Is the work done different in both cases ?
yes.
> How can you relate your "work being done" with the
> above facts ?
How do you relate the work done in moving 1 kg in 10 second a distance of
one foot on a friction free table with the work done moving the same mass
the same distance in 100 seconds? The second case takes much less force so
there is much less work done.
>> > The fact is that the horizontal motion of the center of mass
>> > of the gyroscope occurs at constant speed - wp - the
>> > precession angular frequency. To have a force you need
>> > accelerated motion and you don't have that accelerated
You confuse force and acceleration. You think acceleration causes force
whereas force causes acceleration.
My car runs out of gas. I get out and push. The force I apply accelerates the
car. The car's acceleration does NOT cause the force.
>> > motion on the precession plane.
>> > Force = mass x acceleration
>> > Torque = Moment of inertia x dwp/dt
>> > and dwp/dt = 0 (no acceleration)
>> >
>> > No acceleration = No force = No torque.
wrong
>>
>> Mass sitting on table. rope over pully, weight. Gravity exerts force on
>> weight and pulls rope. Mass on table slides. Sliding friction balances
>> G
> and
>> mass moves at constant velocity.
>>
>> Work is done. Remove force of gravity (weight) and movement/work stops.
>>
>> Gyro is similar. Do experiment in zero G. Substitute force pulling on
>> rope for gravity. Remove force, precession stops.
>
> Gyro is not similar.
A gyro precessing under the influence of gravity is. See the rope to pully on
ceiling example again.
>> >> The acceleration of gravity did the work.
>> >
>> > The force of gravity produces no work.
>> > We have already seen this above.
>> > Nor in the vertical plane, nor in the horizontal plane.
>> >
>> > If the force of gravity produces work we will have free
>> > energy and a perpetual machine of first kind.
>>
>> Not free. But falling water produces work. The force of gravity does
>> the work.
>
> Only when it falls
> Nothing falls in the gyro.
The force of gravity is precessing the gyro.
> Nothing accelerates in the gyro and nothing falls.
Look at the definition of work. W=Fd. Why didn't they define it on the basis
of Acceleration rather than force? Do you think there might have been a
reason?
> http://physics.nad.ru/Physics/English/gyro_tmp.htm
>> You are confusing acceleration and force. The FORCE of gravity produces
>> an acceleration in a body that is free to fall.
>
> F = ma
> What is wrong about F = ma ?
nothing is wrong with it.
> What I'm confusing ?
The cause and the effect.
> The mass is there and to have a force over that mass Newton
> says I need an acceleration.
You are seeing force as the RESULT of acceleration.
a=F/m is probably the better way to write the equation. And equally valid as
mass is a scalar while acceleration and force are vectors.
>> The FORCE of gravity will produce a constant velocity fall when the
>> fall is opposed by a force.
>>
>> Example: Sky diver falling at terminal velocity. Work being done by
>> gravity.
>> Force times distance. Diver is not accellerating because the force of
>> air friction is in equilibrium with force of gravity.
>
> You have and opposite force (air resistance) that is proportional
> to the fall speed squared. That's why you get constant speed,
> because the opposite force depends on the speed square and
> so there is a speed where both forces balance.
right.
>
> Where do you see a dissipative force proportional to
> angular speed square in the gyroscope ?
>
I see in both an object changing position due to the influence of gravity.
The rate of change of position is constant in both cases.
I said nothing about speed squared in either case.
>
>> ...
>> >> no, the angular momentum of the system is conserved, not constant.
>> >
>> >
>> > If the initial angular momentum is a constant function (it does
>> > not depend on time) and you claim that angular momentum
>> > is conserved, then it is obvious that the final angular
>> > momentum also must not depend on time (is constant).
>> >
>>
>> I didn't say it didn't depend on time. Angular velocity is d_theta/d_t.
>
> Yes, but it is a constant speed.
> d_theta/d_t = 0
>
Theta is changing at the precession rate.
>
>> If you have angular velocity of any component of the system changing
>> with time, then you must take this into account in computing the total
>> angular momentum.
>
> Nothing changes in time (short time):
> http://physics.nad.ru/Physics/English/gyro_tmp.htm
sorry, it wants me to download a plugin. I want to be on a 'safe to mess up'
machine when I do things like that.
>
>
>
>> >> > is
>> >> > constant. Hence, the main angular momentum is
>> >> > constant and conserved.
>> >>
>> >> no. Total angular momentum is conserved. Main angular momentum
>> >> changes.
> It
>> >> is a vector. When the direction changes, it changes.
>> >
>> > The magnitude is conserved, not the direction.
>> > I agree.
>>
>> The direction of the total angular momentum of the system is conserved
>> because angular momentum is a vector and angular momentum is conserved.
>
> The direction of the total angular momentum is rotating
> at precession angular speed.
NO. The direction of the gyro's angular momentum vector is rotating at
precession angular speed.
The gyro angular momentum is NOT the total angular momentum, which is
conserved. Total angular momentum is NOT rotating.
>
>
>
>> ...
>> >> Wrong. The total angular momentum OF THE SYSTEM is conserved. The
> forces
>> >> and torques must be included in the calculations of the total
>> >> angular momentum.
>> >
>> > Well, now you include forces and torques in the angular momentum.
>> > How to you translate a torque into angular momentum ?
>>
>> When the torque attempts to change the angular momentum by changing the
>> direction of the vector I, a resultant force is produced at 90 degrees
> that
>> keeps the total angular momentum constant.
>
> What force is produced at 90 degrees ?
> To apply force over a free body you need to apply
> acceleration.
acceleration is the result of a force, not the cause of it.
> You don't have acceleration, nor any explanation
> for the fact that precession depends on the main
> angular momentum.
> wp = mg r / L
>
you have cause and effect confused.
>
>
>> > Notice that:
>> > Torque = dL/dt
>> > And you claim that L = constant.
>>
>> The sum of the angular momenta must be constant. If you attempt to
>> change
> the
>> angular momentum, your angular momentum must change to keep the sum
>> total constant.
>
> I agree.
> That's why I keep saying that it only works for gravity.
And I showed that gravity is not unique. ANY force applied properly will
cause precession. See my rope-pully on ceiling example.
>
>
>> Under zero G, if you try to turn a screw, you turn.
>>
>> Do the physics lab experiment with the bicycle tire.
>>
>> Go into a bar with bar stools that freely rotate. Sit on one and try
> spinning
>> a large mass with its axis of spin over the axis of rotation of the bar
>> stool. Angular momentum is conserved and you will spin in the other
>> direction.
>>
>> Do the gyro experiment, holding onto one end of the bicycle wheel axis,
>> holding the axis out, parallel to the ground, support it only on one
>> end. Keep that end at a constant hight. When gravity pulls the COG
>> downward,
> you
>> will turn. You precess with the gyro. Gravity is doing work. It moves
>> the center of mass of the system 'you, wheel, bar-stool-top'. The
>> distance
> moved
>> times the force of gravity is the work done.
>
> Right.
> Only when gravity pulls the COG downward I will turn.
> Once down it stops.
> Here I do see the accelerated motion - the fall.
accelerated motion is not vital. The force is the cause.
>
>
>> ...
>> >> wrong. W=Fd, gravity exerts a force and the COG moves a distance.
>> >> The
> fact
>> >> that it moves at right angles to the force is NOT important. The
>> >> force
> and
>> >> the distance are the important thing.
>> >
>> >
>> > So, when I have a mass on the top of an horizontal table
>> > and I move that mass (no friction) horizontal on the table
>> > I'm producing work against gravity ?
>>
>> When you move the mass, whether or not there is friction, you do work.
>>
>> Against gravity? NO, I made no such claim about moving an object on a
>> frictionless plane.
>>
>> Gravity moves the Center of Gravity of the gyro. Gravity does work.
>
> And why is that different from moving an object on a
> frictionless plane, against gravity of course ?
>
It isn't. If I move something on a frictionless plane, I do work.
If I use a weight to pull the object, changing direction of force, gravity
does work.
If the plane has friction and the object moves at a constant velocity,
gravity does work.
-- bz please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. bz+sp@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
- Next message: bz: "Re: Photons shapeshifting to wave prior to measurement"
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