Work out force transmitted to sensor

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Discussion Overview

The discussion revolves around calculating the force transmitted to a sensor in a wind tunnel force balance system, specifically focusing on the drag and lift forces acting on a test object. Participants explore the mechanics of lever systems, torque, and the resolution of forces into components, addressing both theoretical and practical aspects of the problem.

Discussion Character

  • Homework-related
  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant questions whether the force transmitted to the sensor is simply the drag force of 1.20 N.
  • Another participant clarifies that the sensor measures drag, not lift, and suggests that the force transmitted will involve the lever lengths.
  • Some participants propose that the torque generated by the forces must be considered to determine the force on the sensor.
  • There is a calculation presented that suggests the transmitted force to the sensor is 2.88 N based on torque and lever arm lengths.
  • Participants discuss how to resolve the forces into horizontal and vertical components, with some confusion about the signs and values of these components.
  • One participant expresses uncertainty about the vertical component being zero, while others clarify that all forces must sum to zero in both horizontal and vertical directions.
  • There is a suggestion to create a free body diagram to visualize the forces acting on the system.
  • Multiple participants engage in deriving equations for the forces at the pivot point, leading to varying interpretations of the results.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the exact values of the forces transmitted to the sensor or the components at the pivot. There are competing views on how to approach the calculations and the significance of the lever arms in determining the transmitted force.

Contextual Notes

Participants express confusion regarding the relevance of lever lengths and the correct application of torque in their calculations. There are also discussions about the assumptions made in defining positive directions for the forces.

Who May Find This Useful

This discussion may be useful for students studying mechanics, particularly those working on problems involving forces, torque, and lever systems in a physics or engineering context.

  • #31
Thought it might be worth checking that the torque really do sum to zero. If clockwise is +ve then...

Summing the torques about the pivot point gives..

(FD * 1.2) - (FS* 0.5) = ?
(1.2 * 1.2) - (2.88 * 0.5) = ?
1.44 - 1.44 = 0

So that's ok.

However if it's not accelerating in rotation you can actually sum the torques about any point and it will be zero. eg It doesn't have to be a real pivot.

Suppose we pick the sensor and sum the torque about that point. The equation is..

(FD*1.2) + (FL*0.5) +(FY*0.5) = ?

FX and FS don't feature because they pass through the point where the sensor is located (eg tangential distance = 0).

Substitute values..

(1.2*1.2) + (1.75*0.5) + (-4.63*0.5) = ?

1.44 + 0.875 - 2.315 = 0

This ability to pick any point about which to sum torques is handy. For example suppose there is an unknown force somewhere. If you pick the point where that force acts you eliminate it from the equation at a stroke.
 
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  • #32
We learned about this in my lectures this semester and I couldn't visualise it too well, but you've helped me understand it a lot better thank you!
 

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