Could Fictitious forces accelerate and change the CoM through internal mass transfer?

[John2020]

Where exactly those internal forces will appear?

[Ghideon]

6 minutes ago, John2020 said:

Where exactly those internal forces will appear?

There are many internal forces. From an engineering point of view I would try to reduce the problem to something simpler, depending on the requirements. For questions about internal forces I would look at specific parts of the system in isolation, not the system as a whole. If for instance the tension in the belt is an issue I would start there.  

[John2020]

Just now, Ghideon said:

There are many internal forces. From an engineering point of view I would try to reduce the problem to something simpler, depending on the requirements. For questions about internal forces I would look at specific parts of the system in isolation, not the system as a whole. If for instance the tension in the belt is an issue I would start there.  

We have to ignore tensions and stuff, just the action reaction principle I would like to involve. For me there remains still an issue: Mass m_T is accelerating without applying a contact force. Is this correct?

[Ghideon]

1 minute ago, John2020 said:

Mass m_T is accelerating without applying a contact force. Is this correct?

A free body diagram of the mass m_T will show contact force. The contact force's magnitude will depend on belt acceleration and mass m_T.

(Im Assuming that the glue is strong enough to hold de mass m_T in place on the belt )  

 

 

[John2020]

7 minutes ago, Ghideon said:

A free body diagram of the mass m_T will show contact force. The contact force's magnitude will depend on belt acceleration and mass m_T.

(Im Assuming that the glue is strong enough to hold de mass m_T in place on the belt )  

In Fig.1 it appears the mass m_T to accelerate without a contact force. How the free body diagram assumes one from the moment there is none (just a varying momentum)?

[Ghideon]

7 minutes ago, John2020 said:

In Fig.1 it appears the mass m_T to accelerate without a contact force.

Fig 1 and its description was found to be ambiguous, I will not comment on that until it is clarified.

7 minutes ago, John2020 said:

How the free body diagram assumes one from the moment there is none (just a varying momentum)?

One can draw a contact force and then apply the correct laws of physics and mathematics to the situation. A negative contact force usually means one have assumed wrong direction. A zero contact force can happen. Zero gravity and zero friction is one case where contact forces will be calculated to zero.

 

 

Edited October 2, 2020 by Ghideon

[John2020]

Just now, Ghideon said:

One can draw a contact force and then apply the correct laws of physics and mathematics to the situation.

But effectively there is no contact force, otherwise I would have drawn it. One cannot apply a contact force to apply the laws of physics from the moment there is none. It is just a changing momentum of m_T. Isn't this correct?

Assuming there is no dissipation of energy due to friction, the changing angular momentum of the gear is converted to linear acceleration on m_T without applying a contact force. Isn't that right?

Furthemore, let us say mass m_T accelerates with 1 m/sec^2 to the right as seen in Fig.1. Is there a counter acceleration on the rest of the isolated system?

12 minutes ago, Ghideon said:

One can draw a contact force and then apply the correct laws of physics and mathematics to the situation. A negative contact force usually means one have assumed wrong direction. A zero contact force can happen. Zero gravity and zero friction is one case where contact forces will be calculated to zero.

Let us switch to the old thread that was recently closed for a moment. Does your statement above applies for the mass m_T (blue component) on  the construction of the linear actuator?

[Ghideon]

What is your definition of a contact force? Just to reduce the risk if any language issues (on my part)

If you wish to discuss the contact forces and mass m_T maybe you could provide a free body diagram of m_T?

 

16 minutes ago, John2020 said:

Let us switch to the old thread that was recently closed for a moment.

No, that is off topic. 

 

Edited October 2, 2020 by Ghideon
better wording

[John2020]

4 minutes ago, Ghideon said:

What is your definition of a contact force? Just to reduce the risk if any language issues (on my part)

If you wish to discuss the contact forces and mass m_T maybe you could provide the required free body diagram?

What I am trying to say is that on m_T applies no contact force. Only in Fig.2 we have contact forces the action-reaction pair FA and FR.

4 minutes ago, Ghideon said:

No, that is off topic.

It is the same topic. If you insist that we have in both threads a contact force on m_T then I ask from the moderator to close this thread too. It is a waste of time for you and for me.

Edited October 2, 2020 by John2020

[Ghideon]

27 minutes ago, John2020 said:

What I am trying to say is that on m_T applies no contact force.

Mass m_T is accelerated by a force that requires contact; you said m_T is glued to the belt. 

What is the definition of a contact force according to you?

 

(Note: I'm assuming we discuss a macroscopic case, not subatomic particle interactions or chemical process in the glue layer) 

Edited October 2, 2020 by Ghideon
added bottom note; macroscopic case

[John2020]

11 minutes ago, Ghideon said:

Mass m_T is accelerated by a force that requires contact; you said m_T is glued to the belt. 

What is the definition of a contact force according to you?

I stated that mass m_T is one with the belt (rubber). I used the word "glued" to point that the belt and the mass m_T is one indistinguishable (melted belt together with mass m_T). 

Contact force means for me, something that will effectively push mass m_T (like pushing with bear hands a car. The hands contact the surface of the car in this case). Here as also in the mass m:T on the translation screw there is no push (no contact with something that pushes it). Therefore, in both cases we have a pure inertial force (a pure varying momentum of mass m_T). It is a conversion of angular momentum to linear without having a contact force.

Edited October 2, 2020 by John2020

[Ghideon]

15 minutes ago, John2020 said:

I stated that mass m_T is one with the belt (rubber). I used the word "glued" to point that the belt and the mass m_T is one indistinguishable. 

Ok. If they are indistinguishable then we do not look at any internal forces in the belt or between belt, we ignore those internal forces. Note that the forces are still there. The forces do not disappear, the belt can still snap if the belt is too weak to accelerate the mass m_T. And the forces we now ignore are contact forces.

As requested we look at the belt and mass m_T as one inseparable whole. If we neglect the belt mass we have a subsystem composed of belt and the box with a total mass m_T. The belt is accelerated by the contact forces between the belt and the drive wheel.The mass m_T is still accelerated by contact forces.

 

15 minutes ago, John2020 said:

translation screw

Off topic

Edited October 2, 2020 by Ghideon

[Ghideon]

4 minutes ago, John2020 said:

I cannot see them, otherwise I would have drawn them.

here:

5 minutes ago, Ghideon said:

The belt is accelerated by the contact forces between the belt and the drive wheel.

 

 

[John2020]

Just now, Ghideon said:

The belt is accelerated by the contact forces between the belt and the drive wheel.

These are contact forces between the belt and the drive wheel not upon the surface of mass m_T.

The moderators are probably sleeping. Hey, wake up! You have to close this thread!

[Ghideon]

Just now, John2020 said:

These are contact forces between the belt and the drive wheel not upon the surface of mass m_T.

Yes since you wanted me to look at them as an inseparable whole. The contact force (belt-glue-box) is still there. As I stated above in case you missed it.

 

Maybe we should consider the possibility that you have not argued in good faith? Note: Trying to arrange an obscure or unclear example to get supporting comments regarding reactionless drives does not work here.

[John2020]

1 minute ago, Ghideon said:

Maybe we should consider the possibility that you have not argued in good faith? Note: Trying to arrange an obscure or unclear example to get supporting comments regarding reactionless drives does not work here.

OK. Thread is closed!

[Ghideon]

1 minute ago, John2020 said:

OK. Thread is closed!

Is that another way of saying "Ops, I was wrong" ?

[John2020]

1 minute ago, Ghideon said:

Is that another way of saying "Ops, I was wrong" ?

Maybe I am wrong on this thread but certainly not  on the other with the translation screw.

7 minutes ago, Ghideon said:

The contact force (belt-glue-box) is still there

I still cannot see it. Do you see any contact force pushing the mass m_T (is there any bare hands pushing and I am so blind I cannot see them?)

[Ghideon]

 

7 minutes ago, John2020 said:

I still cannot see it. Do you see any contact force pushing the mass m_T (is there any bare hands pushing and I am so blind I cannot see them?)

I'll try to make a picture describing the situation. But if you have basic issues with Newtonian mechanics this forum is the right place to ask questions; many members are quite skilled and helpful.

Maybe you could start a fresh thread with a less obscure example? Er even better, asking someone to describe contact forces using their own best examples? 

 

7 minutes ago, John2020 said:

Maybe I am wrong on this thread but certainly not  on the other with the translation screw.

OT, I am not sharing your opinion regarding that topic.

 

Edited October 2, 2020 by Ghideon

[John2020]

2 minutes ago, Ghideon said:

OT, I am not sharing your opinion regarding that topic.

IF you carefully read the 18 points I shared on that thread and keep your focus on that Fig and think clearly without being influenced about how you can solve regular classical mechanics problems then there is a high probability to start seeing the light.

[Ghideon]

1 minute ago, John2020 said:

think clearly without being influenced about how you can solve regular classical mechanics problems

Then please post something that is not a regular mechanical problem. So far we have been discussing just basic mechanical constructs and appropriate means of analysis have been applied. 

[Phi for All]

24 minutes ago, John2020 said:

OK. Thread is closed!

!

Moderator Note

Please don't bring this subject up again, since you're unable to support it within the context of our rules.