Muscle Force - Biomechanics of the Human Body - page 98

C.G.

W

O '

N r N l

d

Let us begin by transporting the weight force to the level of the ground. We
choose O 0 as the axis of rotation, at the left foot, for convenience, and apply the
second condition of equilibrium:

M T ¼ (700 N)(0.15 m) N r (0.30 m) ¼ 0,

N r ¼ (105 N m)/0.30 m ¼ 350 N.

By using the second condition of equilibrium we obtain:

N r + N l ¼ W ¼ 700 N,

Hence, as N r ¼ 350 N, N l ¼ 350 N.

Exercise 6.1 Consider a man with 70 kg mass, who injured his left foot, as
illustrated in the figure of Exercise 6.1. As a consequence, the contact force exerted
by the ground on his left foot is changed to 200 N. His feet are 30 cm apart. Find the
distance of the injured foot to the line that passes through the C.G. Calculate also
the contact force exerted by the ground on the good right foot.