For the purposes of this problem, we’ll assume a simple model of the operation of your foot and ankle. We’ll assume that your foot pivots as a single structure about a single pivot in the ankle. This simple model will help us explore the operation of the ankle joint and draw some interesting conclusions. Let’s take your foot as the object of interest. When you stand on tiptoe, your foot pivots about your ankle. As shown, the forces on one foot are an upward force on your toes from the floor, a downward force on your ankle from the lower leg bone, and an upward force on the heel of your foot from your Achilles tendon. Suppose a 61 kg woman stands on one foot, on tiptoe, with the sole of her foot making a 25° angle with the floor; the distances are as shown. What is the magnitude of the tension force in the tendon? By what fraction does this force exceed the woman’s weight? What is the magnitude of the force in the ankle joint?
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Her foot pivots as a single structure about a single pivot in her ankle. When she stands on tiptoe, her foot pivots about her ankle. As shown in the foot diagram and the free-body diagram below, the forces on one foot are an upward force on her toes from the floor, a downward force on her ankle from the lower leg bone (called the Tibia), and an upward force on the heel of her foot from her Achilles Tendon.
Suppose a 61.3 kg woman stands on one foot, on tiptoe, with the sole of her foot making a 25.0 degree angle with the floor, and with the distances are as shown in the figure.
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