Equal to zero if angular velocity is constant

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Discussion Overview

The discussion revolves around the relationship between angular velocity, normal acceleration, and tangential acceleration in rotational motion. Participants explore which type of acceleration is equal to zero when angular velocity is constant, considering various scenarios including mechanisms and motion on flat surfaces.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that tangential acceleration is zero when angular velocity is constant, indicating uniform motion.
  • Others clarify that while angular velocity remains constant, the direction of tangential velocity changes, implying that tangential acceleration is not necessarily zero.
  • There is a discussion about the nature of normal acceleration, with some participants asserting that it is directed towards the center of rotation and is not zero if the object is in motion.
  • A participant questions whether normal acceleration can be zero in the case of a sliding block on a flat surface, leading to further exploration of the conditions under which normal acceleration may be considered zero.
  • Another participant emphasizes that normal acceleration cannot be zero if the object is rotating, referencing the formula for centripetal acceleration.
  • There is confusion regarding the definitions and implications of tangential and normal acceleration, with requests for summaries and clarifications on how to determine which is zero in different situations.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether normal or tangential acceleration is zero under the condition of constant angular velocity. Multiple competing views and interpretations remain throughout the discussion.

Contextual Notes

Participants express uncertainty regarding the definitions and applications of tangential and normal acceleration, particularly in different mechanical contexts. There are unresolved questions about specific scenarios, such as the behavior of a sliding block on a flat surface.

darkmagic
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Homework Statement



Which is equal to zero if angular velocity is constant, normal or tangential acceleration?
The one with zero angular velocity is a crank. The crank moves at a fixed point.

Homework Equations





The Attempt at a Solution

 
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darkmagic said:

The Attempt at a Solution


So which do you think it is and why?
 


I think it is the tangential one because that means it is a uniform motion but continuously changing speed? is that correct?
 


darkmagic said:
I think it is the tangential one because that means it is a uniform motion but continuously changing speed? is that correct?

But it is not changing speed, the angular velocity is the same.

At different points in the circular motion, if you draw a tangent to the circle, you will get the direction of velocity right? Does this tangent always point in the same direction?
 


sorry it should be constant velocity. changing direction but constant speed, right?
 


darkmagic said:
sorry it should be constant velocity. changing direction but constant speed, right?

Yes. So would the tangential velocity be changing is α is defined as α=dω/dt ? Since the direction of the tangential velocity is changing what does that say about acceleration?
 


velocity is changing. If that is changing, acceleration is also changing?
 


darkmagic said:
velocity is changing. If that is changing, acceleration is also changing?

Right so if you were to draw the two velocity tangents and then find the change in velocity, it would point towards the center of rotation. So which acceleration is zero?
 


Normal acceleration is always towards the fixed point. The normal one?
 
  • #10


darkmagic said:
Normal acceleration is always towards the fixed point. The normal one?

That would be correct.
 
  • #11


Can you give a summary on how to determine which is zero among the two in different situations?

How can I determine the tangential acceleration if I have given the angular velocity?
 
  • #12


darkmagic said:
Can you give a summary on how to determine which is zero among the two in different situations?

How can I determine the tangential acceleration if I have given the angular velocity?

tangential acceleration is related to α by atangential=αr
 
  • #13


so, if normal is zero, then tangential equals the angular acceleration. I only depend on the tangential and normal formula.
 
  • #14


darkmagic said:
so, if normal is zero, then tangential equals the angular acceleration. I only depend on the tangential and normal formula.

no no, the only way for your normal acceleration to be zero is if the object is not spinning. Remember a=ω2r
 
  • #15


so normal is zero in a sliding block?
 
  • #16


darkmagic said:
so normal is zero in a sliding block?

You mean a sliding block on a curved surface? No, the normal is not zero. In that case there is still a normal acceleration.
 
  • #17


i mean in a mechanism, in a flat surface. the sliding block has zero normal? I'll be back.
 
  • #18


darkmagic said:
i mean in a mechanism, in a flat surface. the sliding block has zero normal? I'll be back.

Once your object is basically rotating with respect to some point, there will be a normal acceleration.
 
  • #19


I mean in a mechanism, the sliding block, the normal in a flat surface is zero?
 
  • #20


darkmagic said:
I mean in a mechanism, the sliding block, the normal in a flat surface is zero?

ok, what sort of mechanism are you talking about?
 
  • #21


its only a sample, only a schematic drawing.
 
  • #22


darkmagic said:
its only a sample, only a schematic drawing.

Can you post a picture of the schematic?
 
  • #23


its only a sketch angular velocity at 2 is constant
 

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  • #24


darkmagic said:
its only a sketch angular velocity at 2 is constant

If your surface is flat in that manner, then there is no normal acceleration.
 
  • #25


what is the normal acceleration doing?
 

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