Concept explainers
A 35-N hand and forearm are held at a 45° angle to the vertically oriented humerus. The CG of the forearm and hand is located at a distance of 15 cm from the joint center at the elbow, and the elbow flexor muscles attach at an average distance of 3 cm from the joint center. (Assume that the muscles attach at an angle of 45° to the bones.)
a. How much force must be exerted by the forearm flexors to maintain this position?
b. How much force must the forearm flexors exert if a 50-N weight is held in the hand at a distance along the arm of 25 cm? (Answers: a. 175 N; b. 591.7 N)
a)
To determine: The force exerted by the forearm.
Answer to Problem 3AP
The force exerted by the forearm is
Explanation of Solution
Calculation:
Consider torque acts on the counter clockwise direction for forearm of the hand will be taken as positive and the torque acts on the clockwise direction for joint center of the elbow will be taken as negative.
Express the magnitude of the net torque acts on the joints.
Here,
Rewrite the equation (I) for the net forces acts on the joints of the hand.
Here,
Substitute
Therefore, the force exerted by the forearm is
b)
To determine: The force on the forearm flexors exerts on the weight hold in the hand.
Answer to Problem 3AP
The force on the forearm flexors exerts on the weight hold in the hand is
Explanation of Solution
Calculation:
Rewrite the equation (I) for the net forces acts on the weight holds in the hand.
Here,
Substitute
Solve the relation for
Therefore, the force on the forearm flexors exerts on the weight hold in the hand is
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Chapter 13 Solutions
Basic Biomechanics
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