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Even when the head is held erect, as in Figure 9.40, its center of mass is not directly over the principal point of support (the atlanto-occipital joint). The muscles at the back of the neck should therefore exert a force to keep the head erect. That is why your head falls forward when you fall asleep in the class. (a) Calculate the force exerted by these muscles using the information in the figure. (b) What is the force exerted by the pivot on the head?
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<b>Figure 9.40</b> The center of mass of the head lies in front of its major point of support, requiring muscle action to hold the head erect. A simplified lever system is shown.
Figure 9.40 The center of mass of the head lies in front of its major point of support, requiring muscle action to hold the head erect. A simplified lever system is shown.
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Final Answer
  1. $25\textrm{ N}$
  2. $75 \textrm{ N}$
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OpenStax College Physics Solution, Chapter 9, Problem 32 (Problems & Exercises) (1:42)

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