Passage
The effects of gravity are effectively negated if an object is in free fall. For example, an object orbiting the Earth experiences an apparent weightlessness known as microgravity. Because the human body evolved under the influence of Earth's gravity, human physiology undergoes several changes in microgravity environments. Puffy face syndrome (PFS) occurs when an astronaut's extracellular fluid shifts toward upper body regions, resulting in facial bulging and leg shrinkage. Elongation of the spinal column also occurs as intervertebral discs (spinal cartilage) decompress, making astronauts up to 6 cm taller.Researchers simulated microgravity-induced spinal elongation on Earth by suspending 50 volunteers by the arms, holding each above the ground in an upright position. The thickness of each intervertebral disc was measured prior to and following 10 minutes of suspension. Researchers then compared the percentage change in intervertebral disc thickness to similar measurements recorded in microgravity, as shown in Figure 1.
Figure 1 Percentage change in intervertebral disc thicknessIn theory, spinal elongation would also occur in reduced-gravity environments like the surface of the Moon, where the acceleration of gravity is one-sixth that observed on the Earth's surface.
-Ignoring any attachments between the spinal discs and vertebrae, how would static friction between these anatomical structures compare for a person standing on the surface of the Moon to a person standing on the surface of the Earth?

Question

Passage
The effects of gravity are effectively negated if an object is in free fall. For example, an object orbiting the Earth experiences an apparent weightlessness known as microgravity. Because the human body evolved under the influence of Earth's gravity, human physiology undergoes several changes in microgravity environments. Puffy face syndrome (PFS) occurs when an astronaut's extracellular fluid shifts toward upper body regions, resulting in facial bulging and leg shrinkage. Elongation of the spinal column also occurs as intervertebral discs (spinal cartilage) decompress, making astronauts up to 6 cm taller.Researchers simulated microgravity-induced spinal elongation on Earth by suspending 50 volunteers by the arms, holding each above the ground in an upright position. The thickness of each intervertebral disc was measured prior to and following 10 minutes of suspension. Researchers then compared the percentage change in intervertebral disc thickness to similar measurements recorded in microgravity, as shown in Figure 1.

Figure 1 Percentage change in intervertebral disc thicknessIn theory, spinal elongation would also occur in reduced-gravity environments like the surface of the Moon, where the acceleration of gravity is one-sixth that observed on the Earth's surface.
-Ignoring any attachments between the spinal discs and vertebrae, how would static friction between these anatomical structures compare for a person standing on the surface of the Moon to a person standing on the surface of the Earth?

Quizplus · Accepted Answer

11ecba2d_12dc_134b_a3bf_0fcd59795823_MD0008_00 Friction refers to the force that resists sliding between two surfaces. Friction negates (partially or completely) any forces that promote sliding. For example, static friction F_fr occurs when the magnitude of the frictional force is greater than the combined magnitude of forces promoting motion. The magnitude of static friction is directly proportional to the coefficient of static friction μ_s, a constant unique to the two surfaces in opposition. Furthermore, the magnitude of static friction is also directly proportional to the normal force N: 11ecba2d_12dc_134c_a3bf_31ae7c4b607b_MD0008_00 where N is commonly equal to the weight of one object in opposition to another. Within the spinal column, for example, the normal force causing contact between the intervertebral discs and the vertebrae is the weight of the body above the discs. Because both mass and μ_s are intrinsic properties they are not affected by situational factors such as gravity. Therefore, only a change in the acceleration of gravity g will influence the magnitude of static friction observed on the surface of the Moon relative to the magnitude of static friction observed on the surface of the Earth (Choice B). Specifically, F_fr on the surface of the Moon will be 1/6 the magnitude of F_fr on the surface of the Earth because g on the Moon is 1/6 the magnitude of g on the Earth. (Choice D) The passage explains that the Moon is a reduced-gravity environment, not a microgravity environment. On the Moon, the effects of gravity are not eliminated. Educational objective: Friction is the force that resists sliding between two surfaces. Static friction is proportional to the normal force and the coefficient of static friction. Reducing gravitational acceleration also reduces the normal force, which in turn reduces static friction by the same degree.

Passage The Effects of Gravity Are Effectively Negated If an Object