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.
-According to the passage, which of the following changes as an astronaut leaves Earth's surface and enters orbit?

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.
-According to the passage, which of the following changes as an astronaut leaves Earth's surface and enters orbit?

Quizplus · Accepted Answer

11ecba2d_12db_01d7_a3bf_8d2847794715_MD0008_00 The center of mass (CM) of a system of point masses is the average of the masses m_i weighted by their displacement r_i from a fixed reference point: 11ecba2d_12db_01d8_a3bf_eb08ee7c542d_MD0008_00 In the case of a body with a non-uniform mass distribution (eg, humans), the CM is closer to the largest collection or concentration of mass. Furthermore, if a shift in mass occurs in one direction (ie, r_i increases or decreases), the CM will also shift in the same direction. According to the passage, an orbit around Earth is a microgravity environment. In microgravity, PFS is observed as extracellular fluid previously contained within lower portions of the body (ie, feet and legs) shifts to the upper portions of the body (ie, chest and head). Consequently, the shift in an individual's fluid mass will result in a shift in the individual's center of mass. (Choice A) Kinetic friction can occur in microgravity because forces other than gravity can act as normal forces. A normal force is a contact force perpendicular to the surfaces producing it. (Choice C) Inertia refers to an object's tendency to oppose changes in motion. Inertia depends only on the characteristics of the object itself (ie, mass), not on external factors such as gravity or position. (Choice D) The mass of the astronaut will not change upon entering low-earth orbit. Consequently, the magnitude of the gravitational force between the astronaut and nearby objects (eg, the spacecraft) will remain the same. Educational objective: The center of mass of a system of masses is the average of the masses weighted by their displacement from a fixed reference point. The center of mass shifts in the same direction as a redistribution of mass.

Passage The Effects of Gravity Are Effectively Negated If an Object