A man holds a 153-N ball in his hand, with the forearm horizontal (see the figure). He can support the ball in this position because of the flexor muscle force , which is applied perpendicular to the forearm. The forearm weighs 18.6 N and has a center of gravity as indicated. Find (a) the magnitude of  and the (b) magnitude and (c) direction (as a positive angle counterclockwise from horizontal) of the force applied by the upper arm bone to the forearm at the elbow joint.

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A man holds a 153-N ball in his hand, with the forearm horizontal (see the figure). He can support the ball in this position because of the flexor muscle force , which is applied perpendicular to the forearm. The forearm weighs 18.6 N and has a center of gravity as indicated. Find (a) the magnitude of  and the (b) magnitude and (c) direction (as a positive angle counterclockwise from horizontal) of the force applied by the upper arm bone to the forearm at the elbow joint.

The image illustrates the anatomy and biomechanics of the human arm during a flexion movement. It highlights the role of the muscles and bones in bending the elbow and lifting an object, in this case, a spherical weight.

**Key Components:**

1. **Upper Arm Bone**: This is the humerus, shown extending from the shoulder to the elbow.

2. **Elbow Joint**: The pivot point where the upper arm bone (humerus) connects with the lower arm bones (radius and ulna). It is marked on the diagram.

3. **Flexor Muscle**: Positioned in the upper arm, this muscle (specifically the biceps brachii) is responsible for bending the elbow. The image shows an arrow labeled "M" depicting the direction of the muscle's force.

4. **Center of Gravity (cg)**: This point indicates the center of mass for the forearm and hand. The placement of the "cg" shows the balance and distribution of weight in the lower part of the arm.

5. **Dimensions**:

    - The distance from the elbow joint to the "cg" (center of gravity) of the forearm and hand is 0.0890 meters.
    - The distance from the flexor muscle's attachment point to the elbow joint is 0.0510 meters.
    - The entire forearm and hand, from the elbow joint to the point where the weight is held, measures 0.330 meters in length.

This diagram serves as an educational tool to understand the forces and mechanics involved in arm movements, particularly in exercises or activities that require elbow flexion and lifting objects.
Transcribed Image Text:The image illustrates the anatomy and biomechanics of the human arm during a flexion movement. It highlights the role of the muscles and bones in bending the elbow and lifting an object, in this case, a spherical weight. **Key Components:** 1. **Upper Arm Bone**: This is the humerus, shown extending from the shoulder to the elbow. 2. **Elbow Joint**: The pivot point where the upper arm bone (humerus) connects with the lower arm bones (radius and ulna). It is marked on the diagram. 3. **Flexor Muscle**: Positioned in the upper arm, this muscle (specifically the biceps brachii) is responsible for bending the elbow. The image shows an arrow labeled "M" depicting the direction of the muscle's force. 4. **Center of Gravity (cg)**: This point indicates the center of mass for the forearm and hand. The placement of the "cg" shows the balance and distribution of weight in the lower part of the arm. 5. **Dimensions**: - The distance from the elbow joint to the "cg" (center of gravity) of the forearm and hand is 0.0890 meters. - The distance from the flexor muscle's attachment point to the elbow joint is 0.0510 meters. - The entire forearm and hand, from the elbow joint to the point where the weight is held, measures 0.330 meters in length. This diagram serves as an educational tool to understand the forces and mechanics involved in arm movements, particularly in exercises or activities that require elbow flexion and lifting objects.
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