Calculating the Force of the Deltoid Muscle to Raise an Arm

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Homework Help Overview

The discussion revolves around calculating the force exerted by the deltoid muscle to raise an arm, considering the forces acting on the arm, including gravity and the shoulder socket force. The problem involves understanding the dynamics of muscle force and its components in relation to angles and mass.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of Newton's laws and the decomposition of forces. There are questions about how to incorporate the angle of the deltoid muscle into calculations and the interpretation of acceleration in the x direction.

Discussion Status

Some participants are attempting to clarify their understanding of force decomposition and the role of angles in the calculations. There is a recognition of confusion regarding the implementation of the angle and the calculation of gravitational force. Multiple interpretations of the problem setup are being explored.

Contextual Notes

Participants express uncertainty about the correct approach and calculations, with one noting a discrepancy between their computed result and the expected answer. There is an emphasis on the need for further guidance to clarify the problem's requirements.

Eggphys
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Homework Statement


The main muscle responsible for raising an arm is the deltoid. The deltoid muscle connects at the upper end of the shoulder, extends over the upper arm bone (humerus), and attaches near the elbow. Effectively there are three forces involved in raising the arm: (i) the force of the deltoid muscle, Fm, acting at an angle of approximately 13.2o with respect to the negative x axis, (ii) the force of gravity, Fg, acting effectively at the centre of mass of the arm located close to the elbow, and (iii) the force of the shoulder socket, Fs, acting on the humerus effectively along the x axis. Assuming the mass of the arm is 1.57 kg, calculate the magnitude of Fm in Newton.




Homework Equations


F=ma



The Attempt at a Solution


I'm not quite sure where to start. I tried using F_x=ma and F_y=ma to work out the net force but not getting the correct answer. Any help would be greatly appreciated. Thanks.
 

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Sorry I made a mistake you can do it with just Newtons law no torques needed . Can you show your actual work force decomposition should work if you didn't do any calculation mistakes?
 
Last edited:
bp_psy said:
Sorry I made a mistake you can do it with just Newtons law no torques needed . Can you show your actual work force decomposition should work if you didn't do any calculation mistakes?
After going over my work abit more I see I have no clue what I am doing:frown:
Im not sure how to implement the angle into the equation or what a is in the x direction(Isnt it 0?)
Would Fy just be Fy=1.56*9.8?
Any help on where to start would be great. Thanks:smile:
 
Eggphys said:
After going over my work abit more I see I have no clue what I am doing:frown:
Im not sure how to implement the angle into the equation or what a is in the x direction(Isnt it 0?)
Would Fy just be Fy=1.56*9.8?
Any help on where to start would be great. Thanks:smile:


So i decided to come at this from another angle. First i solved for Fg,
Fg=1.57*9.8 = 15.39
Then to solve for Fm,
Fm=15.39cos 13.2 = 14.98

But the correct answer is 67.38. I am not sure where to go from here to get the correct answer. Any help would be appreciated. Thanks:smile:
 
Just bumping back to the top.
 

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