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30 cm 4 cm

30 cm 4 cm

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Bone - Muscle 100° 30 cm 4 cm 40 cm (A) (B) FIGURE 1.12 (A) Weight held in hand. (B) A simplified drawing of (A). The dimensions shown in Fig. 1.12 are reasonable for a human arm, but they will, of course, vary from person to person. The weight pulls the arm downward. Therefore, the muscle force acting on the lower arm must be in the up direction. Accordingly, the prime active muscle is the biceps. The position of the upper arm is fixed at the shoulder by the action of the shoulder muscles. We will cal- culate, under the conditions of equilibrium, the pulling force Fm exerted by the biceps muscle and the direction and magnitude of the reaction force F, at the fulcrum (the joint). The calculations will be performed by considering the arm position as a Class 3 lever, as shown in Fig. 1.13. The x- and y-axes are as shown in Fig. 1.13. The direction of the reaction force F, shown is a guess. The exact answer will be provided by the calculations. In this problem we have three unknown quantities: the muscle force Fm, the reaction force at the fulcrum F,, and the angle, or direction, of this force p.
Transcribed Image Text:Bone - Muscle 100° 30 cm 4 cm 40 cm (A) (B) FIGURE 1.12 (A) Weight held in hand. (B) A simplified drawing of (A). The dimensions shown in Fig. 1.12 are reasonable for a human arm, but they will, of course, vary from person to person. The weight pulls the arm downward. Therefore, the muscle force acting on the lower arm must be in the up direction. Accordingly, the prime active muscle is the biceps. The position of the upper arm is fixed at the shoulder by the action of the shoulder muscles. We will cal- culate, under the conditions of equilibrium, the pulling force Fm exerted by the biceps muscle and the direction and magnitude of the reaction force F, at the fulcrum (the joint). The calculations will be performed by considering the arm position as a Class 3 lever, as shown in Fig. 1.13. The x- and y-axes are as shown in Fig. 1.13. The direction of the reaction force F, shown is a guess. The exact answer will be provided by the calculations. In this problem we have three unknown quantities: the muscle force Fm, the reaction force at the fulcrum F,, and the angle, or direction, of this force p.
1-3. Using trigonometry, calculate the angle 0 in Fig. 1.13. The dimensions are specified in Fig. 1.12b.
Transcribed Image Text:1-3. Using trigonometry, calculate the angle 0 in Fig. 1.13. The dimensions are specified in Fig. 1.12b.
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