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Questions and Answers
The two applied forces in a force couple have the same magnitude and orientation but opposite directions.
The two applied forces in a force couple have the same magnitude and orientation but opposite directions.
True
Pure force couples are common in the musculoskeletal system.
Pure force couples are common in the musculoskeletal system.
False
The upper trapezius and serratus anterior muscles work together to produce a moment.
The upper trapezius and serratus anterior muscles work together to produce a moment.
True
The vector sum of the two forces in a force couple is always zero.
The vector sum of the two forces in a force couple is always zero.
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Muscles in the musculoskeletal system are responsible for producing only forces, not moments.
Muscles in the musculoskeletal system are responsible for producing only forces, not moments.
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In design exercises, the external torque should match the internal torque potential of the muscle group.
In design exercises, the external torque should match the internal torque potential of the muscle group.
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When the elbow is flexed at 90°, the internal and external forces are equal to their Y components, producing maximal torque.
When the elbow is flexed at 90°, the internal and external forces are equal to their Y components, producing maximal torque.
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As the position of the joint changes, the external torque remains constant, but the angle of muscle insertion changes, requiring a larger muscle force to produce the same internal torque.
As the position of the joint changes, the external torque remains constant, but the angle of muscle insertion changes, requiring a larger muscle force to produce the same internal torque.
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A person with weak elbow flexors may have difficulty holding an object in position B but not in position A.
A person with weak elbow flexors may have difficulty holding an object in position B but not in position A.
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The internal moment arm of any muscle is greatest when the angle of insertion of the muscle is 45 degrees to the bone.
The internal moment arm of any muscle is greatest when the angle of insertion of the muscle is 45 degrees to the bone.
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The external torque is greater in a deep squat compared to a partial squat, due to the difference in the external moment arm between the knee joint and the line of gravity from body weight.
The external torque is greater in a deep squat compared to a partial squat, due to the difference in the external moment arm between the knee joint and the line of gravity from body weight.
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A small angle of the joint favors a large X component force.
A small angle of the joint favors a large X component force.
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When the angle a of the muscle is $90^\circ$, none of the muscle force is available to produce a flexion torque.
When the angle a of the muscle is $90^\circ$, none of the muscle force is available to produce a flexion torque.
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At an angle a of $45^\circ$, the X and Y components of the muscle force have equal magnitude.
At an angle a of $45^\circ$, the X and Y components of the muscle force have equal magnitude.
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When a is less than or equal to $90^\circ$, the X component of the muscle force produces a distracting force on the joint.
When a is less than or equal to $90^\circ$, the X component of the muscle force produces a distracting force on the joint.
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In the figure, there is an external torque in the sagittal plane due to the forces S and W.
In the figure, there is an external torque in the sagittal plane due to the forces S and W.
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The external torque around a joint is greatest when the resultant external force vector is perpendicular to the body segment.
The external torque around a joint is greatest when the resultant external force vector is perpendicular to the body segment.
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The magnitude of the X and Y components of forces applied to a bone depends on the position of the limb segment.
The magnitude of the X and Y components of forces applied to a bone depends on the position of the limb segment.
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The constant magnitude biceps muscle force (M) is always 120 N.
The constant magnitude biceps muscle force (M) is always 120 N.
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The My component always generates a flexion torque at the elbow.
The My component always generates a flexion torque at the elbow.
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The My component creates a distraction force if it is directed away from the elbow.
The My component creates a distraction force if it is directed away from the elbow.
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The Mx component is always zero when the angle of the joint is 90 degrees.
The Mx component is always zero when the angle of the joint is 90 degrees.
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The torque generated by the force components is always the same regardless of the angle of the joint.
The torque generated by the force components is always the same regardless of the angle of the joint.
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Vector resolution is the process of replacing a single force with two or more equivalent forces.
Vector resolution is the process of replacing a single force with two or more equivalent forces.
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The rotatory component (My) acts parallel to a bony segment.
The rotatory component (My) acts parallel to a bony segment.
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The translatory component (Mx) compresses and stabilizes the joint or distracts the segments.
The translatory component (Mx) compresses and stabilizes the joint or distracts the segments.
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The X-axis is set parallel to the short axis of the segment in force resolution.
The X-axis is set parallel to the short axis of the segment in force resolution.
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The Y-component represents the component of the muscle force that acts perpendicularly to the long axis of the segment.
The Y-component represents the component of the muscle force that acts perpendicularly to the long axis of the segment.
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$\Sigma F_x = 0$ and $\Sigma F_y = 0$ are the equilibrium equations for a free body diagram.
$\Sigma F_x = 0$ and $\Sigma F_y = 0$ are the equilibrium equations for a free body diagram.
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