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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.
-An astronaut drifts through space alongside the edge of a spaceship. The astronaut moves as a rigid body with constant velocity and no rotation. Which of the following occurs when the astronaut strikes a protruding portion of the spaceship with her foot? The astronaut:

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.
-An astronaut drifts through space alongside the edge of a spaceship. The astronaut moves as a rigid body with constant velocity and no rotation. Which of the following occurs when the astronaut strikes a protruding portion of the spaceship with her foot? The astronaut:

Quizplus · Accepted Answer

11ecba2d_12db_9e19_a3bf_c9b009ca307a_MD0008_00 A torque is a rotational force that makes an object spin about a pivot point. A pivot point can be a fixed point such as a hinge or axle seen in mechanical systems. For an unrestrained object like an astronaut floating in space, the pivot point is the center of mass CM. Torque is generated by a force F applied perpendicularly to a lever arm (ie, the structure connected to the pivot point): 11ecba2d_12db_9e1a_a3bf_016400f1ae60_MD0008_00 where θ is the angle between the lever arm and the force, and r is the length of the lever arm. Upon striking the protrusion of the ship, the astronaut's foot experiences an impact force due to the collision. The foot, leg, and torso act as the lever arm between the impact force and the astronaut's center of mass. Therefore, the collision generates a torque about the astronaut's CM, making the astronaut spin (Choice A). The astronaut's translational (ie, non-rotational) motion does not change significantly because gravitational forces are negated in microgravity (Choice B and D). However, the astronaut continues along her original path with reduced velocity because a portion of the impact force acts perpendicular to her original path, causing negative acceleration. Educational objective: Torque is a rotational force that makes objects rotate about a pivot point. For an unrestrained object, the pivot point is the object's center of mass.

Passage The Effects of Gravity Are Effectively Negated If an Object