Ceiling fan and impact force on the blades

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Discussion Overview

The discussion revolves around the impact force of a ceiling fan's blades when one blade strikes a fixed target. Participants explore the design implications of flexible blades and the effects of momentum during impact, drawing parallels to other scenarios, such as a human arm wielding a sword. The conversation includes considerations of whether the design allows for flexing of the blades and how momentum is distributed among them during an impact.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that a design with flexible blades and a flexible central rod could allow for flexing during impact, potentially reducing the force delivered to the target.
  • Others question whether the other blades would have time to flex at the moment of impact, suggesting that the total momentum may act on the blade hitting the target.
  • There is a comparison made to the mechanics of a bat striking a ball, where the timing of deformation and impact is discussed as a critical factor.
  • One participant suggests that if the target is un-fixed, the impact may behave similarly to that of a fixed target, raising questions about the principles of momentum in moving objects.
  • Another participant expresses uncertainty about the clarity of the questions being posed, indicating potential communication issues in the discussion.
  • Some participants acknowledge a lack of consensus on the mechanics involved, with one stating that the total momentum of all blades is affected by the impact of one blade.

Areas of Agreement / Disagreement

Participants express differing views on the mechanics of impact and momentum distribution, with no clear consensus reached on the effectiveness of the proposed design or the behavior of the blades during impact.

Contextual Notes

Participants note assumptions regarding the state of the fan (powered off) at the time of impact and the nature of the target (fixed vs. un-fixed), which may influence the outcomes discussed.

be unique
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A ceiling fan has kinetic Momentum in 1 blade hitting a fixed target. Would the design allow the other blades to flex , reducing target impact? If the 4 blades are combined and bolted together at same velocity is different Momentum delivered?
Similar q : a human arm is about 8kg and a sword about 1 kg. Does the hand-grip cause less impact than if the sword is welded into a steel-pin locked onto arm-bones?
( I'm guessing the answer is 50% maybe and it's not Physics..) ( but photos of skull damage and Newton calcs. suggest "yes" ).
 
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The design of 4 flexible blades and a flexible central ceiling-rod .
 
be unique said:
The design of 4 flexible blades and a flexible central ceiling-rod .
So you are asking us if a design involving 4 flexible blades and a flexible central ceiling-rod would allow the blades to flex?
 
At the moment in time of impact of 1 blade , will the other 3 blades have time to flex or will the total Momentum act on the 1 blade hitting target? This assumes the power is switched off shortly before impact so there is no added energy .
 
be unique said:
At the moment in time of impact of 1 blade , will the other 3 blades have time to flex or will the total Momentum act on the 1 blade hitting target? This assumes the power is switched off shortly before impact so there is no added energy .
See #2.
 
I gather Russ does not know the shape of ceiling fan and JB and I do not know something .
I believe if the target is un-fixed then the impact on it will be the same as if it's fixed. But a moving object with Momentum may have different principles ..
 
Last edited:
be unique said:
I gather Russ does not know the shape of ceiling fan...
I know of several.
 
" When the ball strikes the bat, it causes the bat to bend slightly at the impact point. That bend then propagates along the bat up to the handle, reflects off the end of the handle and then travels back down to the impact point. The bend takes about 0.002 seconds to travel up to the handle and back again. But the ball is on the bat for only 0.001 seconds, and it bounces off before the reflection gets back to the impact point."
It's the missing .001 seconds that worries me .
 
  • #10
@be unique -- are you trolling us, or do you just have really bad language translation software and do not know how to post links to what you are asking about? Try CTRL-C and CTRL-V.
 
  • #11
What links? The answer would be 1) don't know , which is OK by me ,2) total Momentum of all blades is impacted by 1 blade on target or 3) an unknown deformation in the whole fan assembly absorbs a portion of Momentum at impact .
 
  • #12
Ok, well, that's enough. If you are serious about your questions you can PM me with something more coherent and detailed and I will consider adding it to the thread and re-opening it. Otherwise, thread closed.
 

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