The Physics Behind a Ceiling Fan: Understanding Angular Momentum and Stability

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Discussion Overview

The discussion revolves around the physics of a ceiling fan, specifically focusing on angular momentum, torque, and stability. Participants explore the implications of Newton's third law in the context of a rotating fan and the forces acting on it.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions why the anti-clockwise angular momentum of the fan does not lead to instability in the handle, suggesting that it should produce a clockwise torque according to Newton's third law.
  • Another participant explains that in a steady state, the torques acting on the fan and handle are balanced, with the motor and air drag contributing to the overall torque dynamics.
  • A third participant clarifies that constant angular momentum does not produce torque, indicating that it is the drag against the air that generates the necessary torque, not the angular momentum itself.
  • There is a suggestion that the torque produced is not significant enough to cause instability in the handle.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between angular momentum and torque, with some asserting that the torque is minimal while others question the stability of the fan based on Newton's third law. The discussion remains unresolved regarding the implications of these forces on the fan's stability.

Contextual Notes

Participants do not fully explore the assumptions regarding the forces at play or the conditions under which the fan operates, leaving some aspects of the discussion open to interpretation.

Who May Find This Useful

This discussion may be of interest to those studying physics, particularly in the areas of mechanics and dynamics, as well as individuals curious about the practical applications of these concepts in everyday devices like ceiling fans.

STAR GIRL
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Fan makes me wonder the Vicinity of Physics. The fan is rotating at an anti-clockwise direction & it is suspended from the ceiling by a cylindrical handle. Now the fun starts here...

According to Newton's 3rd law every action has its opposite reaction. That means the anti-clockwise angular momentum of the fan should produce a clockwise torque on its handle which will make the handle unstable & forces the fan to fall down.

But this never happens why?
 
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At steady state (not accelerating), the motor exerts an anti-clockwise torque on the fan, the fan exerts an anti-clockwise torque on the air related to drag. The air exerts a clockwise torque on the fan, which in turn exerts a clockwise torque on the motor, which in turn exerts a clockwise torque on the handle, which in turn exerts a clockwise torque on the ceiling (the "ceiling" would exert an anti-clockwise torque on the handle).
 
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STAR GIRL said:
According to Newton's 3rd law every action has its opposite reaction. That means the anti-clockwise angular momentum of the fan should produce a clockwise torque on its handle
Constant angular momentum does not produce torque; the drag of the fan against the air is what produces the torque.
which will make the handle unstable & forces the fan to fall down.

But this never happens why?
It isn't much torque.
 
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Thanks
 

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