Unlike most of the other muscles in our bodies, the masseter muscle in the jaw,

Question

Unlike most of the other muscles in our bodies, the masseter muscle in the jaw, as illustrated in the figure, is attached relatively far from the joint, enabling very large forces to be exerted by the back teeth. This is shown in the figure below, where a person is biting down on a bullet placed between the back teeth. (F_M = 225 N and r_R = 4.1 cm.) Using the information in the figure, calculate the magnitude of the force exerted by the teeth on the bullet. Calculate magnitude of the force on the joint.

Explanation / Answer

Apply Net torque about joint = 0

FM*rM - F_reaction*rR = 0

F_reaction = FM*rM/rR

= 225*2.9/4.1

= 159.1 N <<<<<<<<<<-----------------Answer

Apply, Fnety = 0

FM - FJ - F_reaction = 0

F_J = FM - F_reaction

= 225 - 159.1

= 65.9 N <<<<<<<<<<-----------------Answer

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