# Circumventing Newton's third law through Euler Inertial Forces

## Recommended Posts

5 hours ago, John2020 said:

Just assume for a moment it is possible without releasing the energy over a photon. The nucleus and the electron absorb this energy by converting to radial momentum.

Energy and momentum are different things. One cannot convert one to the other.

Quote

I mentioned above we have a rope that is non rigid radially that means the tangential velocity may also change. Thus, at that moment as Ghideon also noted, the Centrifugal will be larger than the centripetal resulting in small mass displacement radially.

OK, you want r to increase. How does a non-rigid rope push the mass?

Quote

Thus, at that moment as Ghideon also noted, the Centrifugal will be larger than the centripetal resulting in small mass displacement radially.

Not in the frame of the observer, as you had described.

Only in the rotating frame is there a centrifugal force. But it’s not a real force, which is confirmed by the fact that a non-rigid body doesn’t push.

• Replies 556
• Created

#### Posted Images

15 hours ago, John2020 said:

Let others answer this if they like

Good idea. In case I made an error there will be an opportunity to learn, and I prefer feedback from those members that possess the required skills to explain the mainstream perspective. Most likely you have failed to realise some of the constraints you have added along the way. You said "imagine the rope cannot curl (being rigid) but is non-rigid radially". That is not a string but more like a tube in a tube with a spring inside (AKA a dynamometer) and as described it will be held and swinged like a solid rod and not a string. Maybe we need to redo the example from the beginning and you state all assumptions initially instead of adding them later, that will make it easier to check for errors and for others to follow.

@John2020 Note that you asked about experience rather than a mathematic model. Your use of "imagine" and "just assume" may lead to different interpretations, physically invalid, setup and errors. Also note that errors in the analyse says nothing about the correctness of Newton;

15 hours ago, John2020 said:

In the meantime when you have a motor suspended by a thread and start it and let us say starts and stop aftet 1/4 of rotor complete cycle what would the motor do?

Insufficient information is provided. Maybe you could add the details or post your claim so we can correct it?

2 hours ago, swansont said:

Not in the frame of the observer, as you had described.

Only in the rotating frame is there a centrifugal force. But it’s not a real force, which is confirmed by the fact that a non-rigid body doesn’t push.

We are probably discussing different versions of the question; @John2020 changed frame of reference somewhere halfway through the analysis I performed. My answer* is for the when the observer is rotating around the same axis as the string with the ball.

*) Which still means I could be wrong, of course, for instance in the step where the events was moved from earth into space.

Edited by Ghideon
clarification
##### Share on other sites

1 hour ago, Ghideon said:

We are probably discussing different versions of the question; @John2020 changed frame of reference somewhere halfway through the analysis I performed. My answer* is for the when the observer is rotating around the same axis as the string with the ball.

The points stand, though. In the rotating frame the centrifugal force is always present, and doesn’t just show up when you change the radius. And it’s not a real force, because you can’t push a rope.

##### Share on other sites

2 hours ago, swansont said:

The points stand, though. In the rotating frame the centrifugal force is always present, and doesn’t just show up when you change the radius.

I agree, and I told @John2020 that*. And asked why there was no centrifugal force was mentioned in step 1 and 3 their analysis.

2 hours ago, swansont said:

And it’s not a real force, because you can’t push a rope.

Also true, for regular (real) ropes. I tried to analyse the imagined string introduced by John2020. Since it is stiff like a a rod except for lengthwise one can increase the speed by increasing angular velocity, the push is not radial.

Conclusion 1: We do not have a well defined situation to analyse and probably never will have in this case.
Conclusion 2: If we started all over and introduce proper definitions I think we would have an agreement regarding mainstream physics.
Conclusion 3: I should not try to analyse OPs examples without asking for lots of more detail in the beginning. Lesson learned.

Edited by Ghideon
##### Share on other sites

13 minutes ago, Ghideon said:

Also true, for regular (real) ropes. I tried to analyse the imagined string introduced by John2020. Since it is stiff like a a rod except for lengthwise one can increase the speed by increasing angular velocity, the push is not radial.

I am preparing a drawing to explain all these and we will make the analysis for three cases: rigid rope, semi-rigid and non-rigid rope.

##### Share on other sites

On 10/18/2020 at 10:48 AM, John2020 said:

Then it has to be utilized in a rotating frame. Creation of an Euler force.

If it doesn't work when seen from an inertial frame of reference then it doesn't work at all.

On 10/18/2020 at 10:56 AM, John2020 said:

In an accelerating spinning chair will appear centrfugal and Euler forces. They should be possible to be  utilized.

The only force that can be utilized is the one that is actually accelerating you. Fictitious force only arise and are present in non-inertial frames of reference because mathematically we attempt to treat an accelerating frame of reference as if it actually is at rest so we have to make up other forces to give rise to the phenomenon we observe while remaining at rest in that non-inertial frame of reference. Those forces which do not disappear after we switch frames of reference from say non-inertial to inertial (centripetal force for example) are the only real forces that you can do anything with.

##### Share on other sites

11 minutes ago, John2020 said:

I am preparing a drawing to explain all these and we will make the analysis for three cases: rigid rope, semi-rigid and non-rigid rope.

For what purpose? If this is a genuine mainstream physics question it may be better in a separate thread since it is not speculative. If it is an attempt to find support for you "interpretation" of Newton it will not work. It may of course still be interesting to find what the misunderstanding is based on, in case learning is still an option.

##### Share on other sites

On 10/18/2020 at 7:23 AM, John2020 said:

Because I addressed the rotational energies coming from the torque (nut) and counter torque (upon the screw), where both have opposing direction of rotation (conservation of angular momentum), thus they cancel each other.

At some point the whole thing is at rest then at a later time it's moving at a constant linear and angular velocity with respect to its center of mass. Thusly, there wasn't actually any conservation of angular momentum or energy because work was done (in this case both linear as well as rotational work). Energy was not in fact conserved if this bolt went from not moving to moving.

26 minutes ago, John2020 said:

I am preparing a drawing to explain all these and we will make the analysis for three cases: rigid rope, semi-rigid and non-rigid rope.

If you are truly to do this correctly you CANNOT be ignorant to what frame of reference you are in whether inertial or in the rotating frame of reference. Further, fully analyze it from the inertial frame of reference then move into the non-inertial one with mathematics to back up your conclusions.

##### Share on other sites

1 hour ago, The victorious truther said:

If it doesn't work when seen from an inertial frame of reference then it doesn't work at all.

I have done several mistakes describing the situation with the Fig.1-Upper. I should have mentioned while the bolt turns with constant angular velocity the frame of the construction rotates in the opposite direction by simultaneously displacing the mass m_T to the right. Under such conditions, the analysis makes sense to be done as seen from the rotating frame of the construction.

1 hour ago, The victorious truther said:

The only force that can be utilized is the one that is actually accelerating you. Fictitious force only arise and are present in non-inertial frames of reference because mathematically we attempt to treat an accelerating frame of reference as if it actually is at rest so we have to make up other forces to give rise to the phenomenon we observe while remaining at rest in that non-inertial frame of reference. Those forces which do not disappear after we switch frames of reference from say non-inertial to inertial (centripetal force for example) are the only real forces that you can do anything with.

Being in the rotating frame of the construction, I was expecting the acceleration of the screw (increasing angular velocity) to induce (over the translation screw) an Euler like force (more accurately an artificially conducted by the translation screw mechanism) that will accelerate the mass m_T to the right. Consequently, since this force wouldn't be created by a real force (like pushing by contact, again according to my expectation), the acceleration of mass m_T would result in the redeployment of the CoM without being able to transfer mass in the opposite direction due to the construction topology, thus the system would accelerate as a whole. This was the initial idea behind the construction in Fig.1-Upper.

Regarding inertial and non-inertial frame of reference, I have to admit is very confusing for me, as also irrelevant (a rotating object will induce those fictitious forces that has to induce and a non-rotating one, will have just plain Newtonian acceleration (if any)).

1 hour ago, The victorious truther said:

Energy was not in fact conserved if this bolt went from not moving to moving.

If the construction could work then, the change in the rotational energy (accelerating screw) would be converted to a change in the kinetic energy of the mass m_T and eventually to the whole system. This transition would force the construction frame to stop rotating (resulting in a non-conservation of angular momentum due to the conversion of rotational to kinetic energy). Again this is my view, which is probably wrong as all the above.

Rotating mass m in outer space.
M: mass of the rotor
m: mass that may move radially
ω: angular velocity
yellow rod: rigid rod

Fcp: centripetal force
Fra: reaction force
Ffr: friction force
Fcf: inertial centrifugal force while Δω ≠ 0

The rotor provides a constant angular velocity while the mass is at distance (r). When the angular velocity increases by Δω within 0.1 radians:
a) How mass (m) will be affected from the change in angular velocity?
b) How the system (M + m) will be affected from the change in angular velocity?

Note: Some years ago, I conducted a very simple experiment with a sample of Pb (lead) metal being suspended by a thread hooked under a weight balance (0.001 grams resolution) and applied a DC magnetic field of Nd Magnet that showed something interesting (video available) that depicts the above situation (according to my view).

Edited by John2020
##### Share on other sites

3 hours ago, John2020 said:

Regarding inertial and non-inertial frame of reference, I have to admit is very confusing for me

Ok, I have noticed that and try to help by providing explanations.

3 hours ago, John2020 said:

(a rotating object will induce those fictitious forces that has to induce and a non-rotating one, will have just plain Newtonian acceleration (if any)).

Vague, incorrect, or both.

A fictitious force is a force that appears to act on a mass whose motion is described using a non-inertial frame of reference, such as an accelerating or rotating reference frame.

3 hours ago, John2020 said:

The rotor provides a constant angular velocity while the mass is at distance (r). When the angular velocity increases by Δω within 0.1 radians:
a) How mass (m) will be affected from the change in angular velocity?
b) How the system (M + m) will be affected from the change in angular velocity?

Edited by Ghideon
##### Share on other sites

3 minutes ago, Ghideon said:

Frame of reference: I am sitting in front of my PC screen (I don't know how you interpret this), seeing the picture of this rotating mass device (Prediction: accelerating in one direction).

Prediction: Mass (m) will accelerate due to the inertial centrifugal force (no reaction will appear at the rest of the system), creating an accelerating change in CoM that will eventually accelerate the system (M+m) as a whole.

Could someone please do the math for whatever prediction? I am just curious how will this problem be handled.

##### Share on other sites

3 hours ago, John2020 said:

Regarding inertial and non-inertial frame of reference, I have to admit is very confusing for me, as also irrelevant (a rotating object will induce those fictitious forces that has to induce and a non-rotating one, will have just plain Newtonian acceleration (if any)).

Newton’s first law tells you. If an object with no real forces on it doesn’t move in a straight line, or it spontaneously starts moving, it’s not an inertial frame.

Inertial frames do not have fictitious forces.

A rotating object does not create fictitious forces.

##### Share on other sites

2 minutes ago, swansont said:

A rotating object does not create fictitious forces.

You mean it should have a mass attached on its surface, at least in order the fictitious forces to manifest?

##### Share on other sites

Just now, John2020 said:

Frame of reference: I am sitting in front of my PC screen (I don't know how you interpret this), seeing the picture of this rotating mass device (Prediction: accelerating in one direction).

Prediction: Mass (m) will accelerate due to the inertial centrifugal force (no reaction will appear at the rest of the system), creating an accelerating change in CoM that will eventually accelerate the system (M+m) as a whole.

Could someone please do the math for whatever prediction? I am just curious how will this problem be handled.

If you aren’t on the object, such that you assume it’s not rotating (but the rest of the room is), then it’s not a rotating frame of reference. IOW, if you can see the object is rotating, you aren’t in the rotating frame

A rotating device obeys Newton’s laws.

Just now, John2020 said:

You mean it should have a mass attached on its surface, at least in order the fictitious forces to manifest?

No, I mean there are no fictitious forces whatsoever in an analysis in an inertial frame.

##### Share on other sites

1 minute ago, swansont said:

No, I mean there are no fictitious forces whatsoever in an analysis in an inertial frame.

So, when I need to make an analysis of a rotating object, I have to place the frame of reference rotating along with the rotating object, right? After finding what is going on there, I switch to the inertial reference (my PC screen) and check how the finding in the rotating object may affect the observation from the inertial frame of reference (my PC screen). I think the @The victorious truther mentioned something similar.

##### Share on other sites

If you are on a carousel, and you ignore the fact that it’s rotating, that’s a rotating frame. If roll a ball from the center to the rim, to you it looks like the ball follows a curved path, even though there’s no force on it.

Newton’s first law tells you that Newton’s laws aren’t going to work. You need to add in a fake force (a Coriolis force) to explain the curved trajectory of the ball.

An observer on the ground sees the ball travel in a straight line, and does not need to appeal to a fake force. They see the carousel rotating, and can use Newton’s laws to analyze whatever motion is observed.

2 minutes ago, John2020 said:

So, when I need to make an analysis of a rotating object, I have to place the frame of reference rotating along with the rotating object, right? After finding what is going on there, I switch to the inertial reference (my PC screen) and check how the finding in the rotating object may affect the observation from the inertial frame of reference (my PC screen). I think the @The victorious truther mentioned something similar.

No, you can analyze it from an inertial frame. In many cases, it’s probably easier to do it that way.

##### Share on other sites

10 minutes ago, swansont said:

No, you can analyze it from an inertial frame. In many cases, it’s probably easier to do it that way.

I think that would lead to wrong conclusions. For e.g. analyzing the rotating mass in outer space (see the drawing I shared a couple of posts above) from an inertial frame of reference, will the motion of the ball (m) be attributed to a real force (and not to inertial centrifugal) that implies a reaction force (upon the rest of the system) appears at the same moment?

I have to go to sleep. See you tomorrow.

Edited by John2020
##### Share on other sites

45 minutes ago, John2020 said:

I think that would lead to wrong conclusions. For e.g. analyzing the rotating mass in outer space (see the drawing I shared a couple of posts above) from an inertial frame of reference, will the motion of the ball (m) be attributed to a real force (and not to inertial centrifugal) that implies a reaction force (upon the rest of the system) appears at the same moment?

Such analyses happen routinely. Compliance with and adherence to Newton’s laws is not a wrong conclusion

##### Share on other sites

5 hours ago, John2020 said:

Prediction: Mass (m) will accelerate due to the inertial centrifugal force (no reaction will appear at the rest of the system), creating an accelerating change in CoM that will eventually accelerate the system (M+m) as a whole.

There is no centrifugal force when seen from your inertial frame of reference.

##### Share on other sites

6 hours ago, swansont said:

Such analyses happen routinely. Compliance with and adherence to Newton’s laws is not a wrong conclusion

Could you make the analysis on the last drawing with the rotating mass and to answer on (a) and (b)?

2 hours ago, The victorious truther said:

There is no centrifugal force when seen from your inertial frame of reference.

Edited by John2020
##### Share on other sites

12 hours ago, John2020 said:

Regarding inertial and non-inertial frame of reference, I have to admit is very confusing for me, as also irrelevant

Understanding frame of reference is relevant if one wish to draw correct conclusions.

8 hours ago, John2020 said:

So, when I need to make an analysis of a rotating object, I have to place the frame of reference rotating along with the rotating object, right? After finding what is going on there, I switch to the inertial reference (my PC screen) and check how the finding in the rotating object may affect the observation from the inertial frame of reference (my PC screen).

I think the two illustrations* below may help describe a rotating frame of reference.
Left frame: We analyse the rotation from a non rotating frame of reference ("PC screen" in your comment) and place an x-y coordinate system on the screen. We see that the ball describes a curved path, a half circle, in that x-y coordinate system*. The ball is accelerating all the time.
Right frame. We place a coordinate system on the rotating circle, for instance painted on the circle's surface. We also choose to place ourselves on the circle and rotate with it. In this coordinate system the ball is stationary, it does not move. The ball has the same coordinates all the time*

Are you following so far? Once you get the difference between the two frames of reference and their coordinate system we may introduce real and fictitious forces and from there move on to:

1 hour ago, John2020 said:

Could you make the analysis on the last drawing with the rotating mass and to answer on (a) and (b)?

I think we should:
-Understand the frame of reference (started above)
-Do the math in rotating frame and inertial frame for your example (a) and (b)
-Compare the outcome and discuss

Agree?

*) (We can neglect the fact that the ball is thrown away at the end of the animation and use the part where ball is attached to string. I had no time to edit the animation)

Edited by Ghideon
##### Share on other sites

13 minutes ago, Ghideon said:

I think we should:
-Understand the frame of reference (started above)
-Do the math in rotating frame and inertial frame for your example (a) and (b)
-Compare the outcome and discuss

Agree?

Very nice animation that demonstrates the difference between the non-rotating and the rotating frame of reference!

I agree (analysis for my example).

##### Share on other sites

1 hour ago, Ghideon said:

Are you following so far? Once you get the difference between the two frames of reference and their coordinate system we may introduce real and fictitious forces and from there move on to:

Yes, we can move on to the analysis.

2 hours ago, Ghideon said:

Right frame. We place a coordinate system on the rotating circle, for instance painted on the circle's surface. We also choose to place ourselves on the circle and rotate with it.

The right frame rotates clockwise. Seeing the rotation of the circle on the left, shouldn't the right frame rotate counterclockwise in order to agree with the rotation of the circle on the left?

##### Share on other sites

2 hours ago, John2020 said:

The right frame rotates clockwise. Seeing the rotation of the circle on the left, shouldn't the right frame rotate counterclockwise in order to agree with the rotation of the circle on the left?

Why?

Note that the two images are describing the same physical situation. Only the coordinate system and point of view differs. Hint regarding the rotation; check the angle between the opening (where the ball escapes, late in the animation) and the string the ball was attached to.

This is important, (and should be obvious):  An event happening in the left image also happens in the right image. Mathematics helps us transform between the different cooridinates the observers would assign to any events*.  If the string brakes and the ball leaves the circular path then that happens in both frames of reference and at the same time*. If the ball is too fragile and is deformed or breaks, that obviously happens in both frames. Observers in both frames agree on the physical effects**,  they just use different coordinates.

Ok so far?

If so the next step is to introduce the forces and make sure they have the same physical effect in both frames of reference.

*) Relativistic effects neglected; low energies and low relative speeds. Relativity of simultaneity / Lorentz is not needed to predict the results with reasonably high precision.

**) For instance that the ball passing through the opening in the square frame late in the animation

##### Share on other sites

12 minutes ago, Ghideon said:

Ok so far?

If so the next step is to introduce the forces and make sure they have the same physical effect in both frames of reference.

It is not clear to me, however not so important for the analysis. Does the rectangular frame has an opposite direction with that of the rotating circle? If yes then, OK. It is like the drawing depicts a situation while being on the circle rotating counterclockwise, the surrounding space turns clockwise. If this is the case then, I agree, otherwise it doesn't make sense to me. However this would negligibly affect the analysis (just the direction the ball follows in your example).

Edited by John2020
##### Share on other sites

This topic is now closed to further replies.

×