Which of the following situations describes a person experiencing $\mathrm{weightlessness}$?

• A. A person in an elevator at rest on the ground floor
• B. A person sitting in a stationary car
• C. A person standing on the surface of the Earth
• D. A person in $\mathrm{free} \mathrm{fall}$ inside a spacecraft orbiting $\mathrm{Earth}$

Answer: (D)

Verified step by step guidance

1. Understand the concept of weightlessness: Weightlessness occurs when a person or object experiences no net contact force supporting it, often because both the person and their surroundings are accelerating at the same rate under gravity, resulting in a sensation of zero weight.
2. Analyze each situation to determine if the person experiences a normal force (which we perceive as weight): For example, a person standing on the Earth's surface feels their weight because the ground exerts an upward normal force balancing gravity.
3. Consider the case of free fall inside a spacecraft orbiting Earth: Both the spacecraft and the person inside are accelerating downward due to gravity at the same rate, so there is no normal force acting on the person, creating the sensation of weightlessness.
4. Recognize that being in an elevator at rest, sitting in a stationary car, or standing on Earth all involve normal forces opposing gravity, so these do not describe weightlessness.
5. Conclude that the correct description of weightlessness is a person in free fall inside a spacecraft orbiting Earth, where the only force acting is gravity and no support force is felt.