Is the force on pole F1 greater than F2 in this torque example?

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Discussion Overview

The discussion revolves around the forces acting on two vertical poles (F1 and F2) in relation to a horizontal pole with an additional weight (B) placed at a distance from F1. Participants explore the implications of torque and force distribution in this setup, questioning the accuracy of a book's explanation regarding which pole experiences greater force.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant assumes that since weight B is farther from pole F1, the force on F1 must be greater than on F2, questioning the book's assertion.
  • Another participant suggests that if the setup resembles a high jump bar, F2 would experience more force due to the unequal distribution of weight, while noting that torque considerations may not have been adequately addressed in the book.
  • A different perspective proposes that if the weight B is split between the poles, then F1 would experience greater force, indicating a conditional relationship based on how the weight is applied.
  • One participant clarifies that torque is not relevant in the initial example, suggesting that the beam must be supported rigidly to handle torque, which complicates the force distribution analysis.
  • A metaphor involving two men holding a plank is introduced to illustrate how the placement of weight affects the forces exerted by each pole, emphasizing that the closer the weight is to one pole, the more force that pole must exert.

Areas of Agreement / Disagreement

Participants express differing views on the distribution of forces between F1 and F2, with no consensus reached on which pole experiences greater force. The discussion remains unresolved regarding the accuracy of the book's explanation and the role of torque in the scenario.

Contextual Notes

Participants note that the book may not have distinguished between torque and force distribution adequately, leading to confusion. The discussion also highlights the importance of how weight is applied in determining the forces on each pole.

JasonRox
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There is an example in the book that goes like this:

F1---------------A----------B--------F2

F1 = Vertical Pole Number 1
F2 = Vertical Pole Number 2
A = Centre of Gravity of Horizontal Pole
B = Extra Weight

The numbers aren't necessary.

Because B is farther away from pole F1, I'm assuming the force on F1 is greater than the force on F2.

The book says otherwise.

Who is right?

Note: The book has been wrong more than once.
 
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Hi, Jason.

If this is set up like a high jump bar, then you'd expect there to be more force acting on F2, because the weight of B is not split equally between F1 and F2. (E.g. if F1 and F2 were your outstretched arms, you would expect F2 to be holding most of the weight.)

However, there would obviously be a greater moment acting (clockwise) about F1 than (anticlockwise) about F2. The book might not have made the distinction between the two.
 
On the other hand, if we cut the bar at B and split the weight of B, greater force will be place on F1, right?

Visual

B/2=C
F1--------------------------C
F2-------C
 
You are closer on your second try, JasonRox. The issue with the first example is that torque isn't relevant there. Assume for a moment that the beam is supported from underneath by pins. The only thing the beam can do to the pins is push down. In your second example, pins wouldn't work - the beam has to be supported rigidly (perhaps with an angled brace) to handle the torque.
 
Maybe this mental image will help: Imagine two men holding each end of a heavy plank. If it's uniform and held level, they exert equal forces to hold up their ends. Now place an additional weight on top of the plank. If that weight was placed in the middle, the two men would share the load. But if it were placed closer to man #2, which man would have to lift harder?
 
Doc Al, that's what I was thinking about the other day. It's all good now.

Thanks, guys.
 

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