A Forces on rotating disk object

[StoyanNikolov]

It can translate, for sure. But this is because the net force is not zero at point 1, unless there is some non-disclosed interaction. You don't need this made-up definition of net force

Please forget Moment 1.
Consider only moment 5.
Rotating object at constant angular velocity and
Applied force at the periphery, not the center of the disk
At what direction the center of mass will go?

 

[TonyStewart]

Please forget Moment 1.
Consider only moment 5.
Rotating object at constant angular velocity and
Applied force at the periphery, not the center of the disk
At what direction the center of mass will go?
View attachment 325677

I forget 1 then I don’t know what is the force vector, radius , direction and momentum for initial conditions undefined. It will tend towards stopping but even the slightest error will have residual motion.

will equal and opposite thrust vectors conserve momentum and kinetic energy or are we debating the illegal assumption an impulse may cause rotational motion without linear motion and assuming it can when it cannot. You need to balance the Force on both sides like in the video!!

if I were given this problem , I would reject it , for the reasons given above.

 

[StoyanNikolov]

I forget 1 then I don’t know what is the force vector, radius , direction and momentum for initial conditions undefined

Initial conditions are :
Rotating disk at constant angular velocity.
Applied force is at the periphery of the disk (not the center)
At what direction the center of mass of the disk
will go after the force is applied . Thank you.
Just like on the attached picture.

 

[Ibix]

At what direction the center of mass of the disk
will go after the force is applied .

What does your link say? I've already told you it has the answer. If you aren't sure you've got the correct answer from it, post what you've understood and we can go from there. If you aren't willing to go to the minimal effort of reading a link you supplied, I'm not willing to spend any more time helping.

 

[StoyanNikolov]

What does your link say? I've already told you it has the answer. If you aren't sure you've got the correct answer from it, post what you've understood and we can go from there. If you aren't willing to go to the minimal effort of reading a link you supplied, I'm not willing to spend any more time helping.

I don't find where it is written about the direction.
Please copy the text from the link, where it is said where the center of mass will go.
If you are willing to go to the maximal effort of not helping me,
it is ok.
Just cannot say that i have the answer for the direction after more than
50 replies on this topic.
Thank you.

 

[TonyStewart]

Initial conditions are :
Rotating disk at constant angular velocity.

How much mass do you need for a tangential force to accelerate rotation of a floating mass yet not accelerate center of mass to some motion as stated In a zero-g environment? Consider the solution to deflection massive asteroids from Earth collision! Even though an asteroid has considerable mass, the purpose of the mission is to deflect the path enough, normal, or perpendicular to the impulse or detonation applied. This has been proven to work.

Applied force is at the periphery of the disk (not the center)
At what direction the center of mass of the disk
will go after the force is applied . Thank you.
Just like on the attached picture.
View attachment 325678

 

[Drakkith]

I don't know what happened with this thread. Perhaps people have lost the forest for the trees. I'll reopen this thread but ask that members please give the OP the benefit of the doubt and that everyone, including the OP, please act as if we were all sitting around a table in person and treat others with respect.

Several off topic or non-helpful posts have been deleted. Thread reopened.

 

[Drakkith]

Please forget Moment 1.
Consider only moment 5.
Rotating object at constant angular velocity and
Applied force at the periphery, not the center of the disk
At what direction the center of mass will go?
View attachment 325677

Assuming other forces are either absent or negligible, it will move upwards.

Consider the situation in which the disk isn't rotating, but a fast moving object moves upwards and strikes the disk at the point you've circled (or some pegs sticking out, or however you want to apply the force). Assuming the disk is not attached to anything else, the center of mass will move upwards. This is the same situation, just without the rotation, which I don't believe matters at all for your question.

 

[A.T.]

Initial conditions are :
Rotating disk at constant angular velocity.
Applied force is at the periphery of the disk (not the center)
At what direction the center of mass of the disk
will go after the force is applied . Thank you.
Just like on the attached picture.
View attachment 325678

- Is the center of mass initially at rest?

- Is the force a short impulse or does it act over a certain period? If the latter, is the direction of the force constant in the inertial frame or in the rotating disk frame?

- Are there any other forces acting?

If there are no other forces, and it is a short impulse, the center of mass will accelerate in the direction of the force. So if it was initially at rest, that's where it will go.

 

[jbriggs444]

Newton's second law original wording (after translation to English):

"LAW II: The alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed."

 

[StoyanNikolov]

- Is the center of mass initially at rest?

- Is the force a short impulse or does it act over a certain period? If the latter, is the direction of the force constant in the inertial frame or in the rotating disk frame?

- Are there any other forces acting?

If there are no other forces, and it is a short impulse, the center of mass will accelerate in the direction of the force. So if it was initially at rest, that's where it will go.

- The center of mass is initially at rest
(There is only rotational motion of the Disk) .
- The force is brief impulse .
- No other forces (only mentioned in the attached picture)

 

[StoyanNikolov]

Assuming other forces are either absent or negligible, it will move upwards.

Consider the situation in which the disk isn't rotating, but a fast moving object moves upwards and strikes the disk at the point you've circled (or some pegs sticking out, or however you want to apply the force). Assuming the disk is not attached to anything else, the center of mass will move upwards. This is the same situation, just without the rotation, which I don't believe matters at all for your question.

Thank you.

If others also want to give opinion are welcome.

 

[jbriggs444]

If others also want to give opinion are welcome.

Everyone here is in agreement. If an object that is not translating is subject to an net upward external impulse, it will begin translating upward.

However, I think that many of us are harboring a suspicion that you are being intentionally coy and are hiding an important part of the scenario from view.

 

[Vanadium 50]

If others also want to give opinion are welcome.

Um, telling other people what they are and are not welcome to do is more likely to make them angry than anything else.

Further, when discussing rotation, it is not a good idea to use the word "moment" to mean an instant in time.

Now, I count this question being answered no fewer than 8 times - including in a link you yourself provided.. If 8 is not enough, how many more? 15? 32? 64?

 

[StoyanNikolov]

Um, telling other people what they are and are not welcome to do is more likely to make them angry than anything else.

Further, when discussing rotation, it is not a good idea to use the word "moment" to mean an instant in time.

Now,, I count this question being answered no fewer than 8 times - including in a link you yourself provided. If 7 is not enough, how many more? 15? 32? 64?

No. It is polite invitation. If you consider yourself angry , please
don't post on this topic.

 

[Vanadium 50]

please
don't post on this topic.

Telling people not to post on "your" topic is not OK.

 

[russ_watters]

Locked pending more moderation. Don't hold your breath.

 

[Drakkith]

Locked pending more moderation. Don't hold your breath.

Thread will remain locked. Any questions, concerns, or comments about this can be directed towards myself or another mentor via a personal message or the report button.