Understanding Surface Gravity and Acceleration in the Moon and Earth

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Discussion Overview

The discussion centers around the concepts of surface gravity and surface acceleration on the Moon and Earth, particularly focusing on the differing values provided by NASA and their implications for physics problems. The scope includes theoretical explanations and conceptual clarifications related to gravitational forces and their variations due to Earth's rotation.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that NASA lists Earth's surface gravity as 9.80 m/s² and surface acceleration as 9.78 m/s², questioning the definition of surface acceleration.
  • Another participant suggests that surface gravity and surface acceleration might be the same, expressing uncertainty about the discrepancy in NASA's values.
  • A different participant proposes that the difference in values could be due to the rotation of the Earth affecting the measurements.
  • One participant explains that surface gravity refers to the gravitational field strength "g" at the surface, while free-fall acceleration is less due to the centripetal acceleration required by Earth's rotation, noting that this acceleration varies by location.
  • Additional resources are provided to support the discussion, confirming that the rotation of the Earth is a factor in the difference between gravitational and free-fall acceleration.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the definitions and implications of surface gravity and surface acceleration. There is no consensus on the exact nature of the discrepancy between the values provided by NASA, and multiple competing views remain regarding the factors influencing these measurements.

Contextual Notes

The discussion highlights potential limitations in understanding the definitions of surface gravity and surface acceleration, as well as the influence of Earth's rotation on these values. There are unresolved questions about the exact nature of the measurements and their implications for physics problems.

Mitchell
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In a Moon/Earth Comparison Data sheet I received from NASA, they list the surface gravity at 9.80 m/s2. They also list surface acceleration at 9.78 m/s2. What is surface acceleration? All the problems relating to gravity in my Physics text (so far) calls Earth's gravity constant as 9.80 m/s2.
 
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Surface gravity is the acceleration due to gravity at the surface of a body (this is used for physics problems that happen close to the ground). I would think surface acceleration is the same thing, but I'm not sure why NASA lists it as 9.78.
 
Maybe they are factoring in the rotation of the earth.
 
THis is due to the effect mentioned in that other thread! (k12 zone) THe "surface gravity" is the actual gravitational field strength "g" at the surface of the earth. The unit of this field strength should properly be N/kg, but this unit is equivalent to m/s^2.

The actual "free-fall" acceleration will be less than "g" because due to the rotation of the earth, some of the gravitaitonal force is required for centripetal acceleration (to keep us going in a circle with the Earth's surface). This surface accelration changes depending on where you are in the world. It is least near the equator, where "g" will be reduced by 0.033 m/s^2.
 
That should satisfy Mitchell. :smile:
 
It sure does and thank you to everyone.
 

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