How does a simple balance scale work?

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Discussion Overview

The discussion revolves around the mechanics of a simple balance scale, focusing on how it achieves equilibrium and responds to varying weights. It includes theoretical considerations and exploratory reasoning about the balance scale's operation.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant describes the basic operation of a balance scale, noting that equal weights result in horizontal balance while unequal weights cause tipping, but questions the physics behind this behavior.
  • Another participant suggests that the pivot point being above the attachment points for the pans contributes to the scale's behavior when it tips.
  • A third participant reiterates the importance of the pivot point's position and introduces the concept of counter torque from the weight of the index needle.
  • A later reply claims to have found a simple explanation regarding the center of gravity of the unladen scale being below the fulcrum, suggesting this creates a restoring torque, and proposes closing the thread.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and explanation regarding the mechanics of the balance scale. While one participant claims to have found a satisfactory explanation, others provide additional insights that suggest ongoing exploration and uncertainty about the complete mechanics involved.

Contextual Notes

Some assumptions about the balance scale's design and the effects of torque and center of gravity are not fully explored or defined, leaving room for further discussion.

f todd baker
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Visualize a simple balance, a pan at either end of a beam which balances on a fulcrum. The way it works is that if each pan carries the same weight, it balances horizontally. If one pan carries slightly more weight, it tips slightly off horizontal. If one pan carries more weight yet, it tips farther off horizontal. But that is not the way it would work if simple physics is applied to my simple model: for equal weights it would balance horizontal or not, and for unequal weights it would rotate fully until it came to a stop, regardless of how unequal they were. There must be some simple explanation, but I have not been able to find it.
 
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The pivot point is slightly above the attachment points for the pans. As the beam tilts right, this means that the rotation moves the pans very slightly left. Similarly, if the beam tilts left, the rotation moves the pans very slightly right.
 
jbriggs444 said:
The pivot point is slightly above the attachment points for the pans.

The weight of the index needle also results in a counter torque.
 
Actually, I found the answer in an earlier thread. It is really quite simple. The center of gravity of the unladen scale is below the point of support (fulcrum) so when the scale tips, there is a restoring torque. I think this thread can be closed.
 

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