Absolute (vacuum) pressure concept: Absolute zero pressure corresponds to which physical condition or location?

Introduction / Context:
Absolute pressure is measured relative to a perfect vacuum, not to atmospheric pressure. Understanding what “zero absolute pressure” truly means prevents mistakes when converting between absolute and gauge pressures and when applying gas laws and vacuum technology concepts.

Given Data / Assumptions:

• Absolute zero pressure means no molecules (or no molecular motion impacting the boundary) in the space considered.
• Sea-level atmospheric pressure is a positive absolute pressure.
• Temperatures must be on an absolute scale (Kelvin) to reason correctly.

Concept / Approach:
Pressure at the microscopic level arises from molecular impacts on surfaces, which are related to molecular momentum transfer. A perfect vacuum has no molecules and hence no momentum exchange, giving zero absolute pressure. Real locations like sea level or the earth's center do not correspond to zero absolute pressure. Temperature statements must also be physically meaningful; there is no such thing as −273 K (Kelvin is non-negative).

Step-by-Step Solution:

Verification / Alternative check:
From kinetic theory, pressure is proportional to number density * mean squared molecular speed * molecular mass. Setting number density to zero yields zero pressure, matching the vacuum concept.

Why Other Options Are Wrong:

• At sea level: Clearly nonzero absolute pressure.
• At −273 K: Non-physical temperature on the Kelvin scale.
• At earth's center: Extremely high pressure due to gravity and overlying mass.

Common Pitfalls:
Confusing gauge pressure zero (which occurs roughly at atmospheric pressure) with absolute zero pressure; mixing Celsius/Kelvin offsets when discussing absolute zero temperature versus vacuum pressure.

Final Answer:
when molecular momentum of the system becomes zero