Is Weight Force an Apparent Force on a Rotating Plate?

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Discussion Overview

The discussion revolves around whether weight force should be considered an apparent force, particularly in the context of a man standing on a rotating plate. Participants explore the implications of this question in both classical mechanics and general relativity, as well as the nature of inertial systems.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants question if weight force is an apparent force, noting that in general relativity it is considered as such, while in classical mechanics it is not.
  • There is agreement that centrifugal force is an apparent force on a rotating plate, but uncertainty remains about the treatment of weight force in this scenario.
  • One participant suggests that when discussing approximately inertial systems, the Earth's rotation around the sun is a factor, but questions whether gravity plays a role in this classification.
  • Another participant provides a technical detail regarding the centripetal acceleration due to Earth's rotation, indicating that it is relatively small compared to gravitational acceleration.
  • Concerns are raised about the implications of apparent weight in practical applications, such as the calibration of scales used in commerce, which must account for centrifugal force.

Areas of Agreement / Disagreement

Participants express differing views on whether weight force is an apparent force, with some supporting its classification as such in general relativity and others opposing it in classical mechanics. The discussion remains unresolved regarding the treatment of weight force in rotating systems.

Contextual Notes

The discussion highlights limitations in understanding the nature of forces in rotating frames and the dependence on the definitions used in different physical theories. There are unresolved questions about the implications of Earth's rotation and gravity in defining inertial systems.

nebbione
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Is the weight force an apparent force ? Sorry but on the web i can't find anything.
For example if i should think about a man that is on a rotating plate,what are the apparent force ?
I think surely the centrifugal force but should i consider even the wight force of the man ?
 
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nebbione said:
Is the weight force an apparent force ?
In General Relativity it is, in classical mechanics it is not.

For example if i should think about a man that is on a rotating plate,what are the apparent force ?
I think surely the centrifugal force but should i consider even the wight force of the man ?
As this is classical mechanics, you can (and should) treat gravitation as a real force.
 
Ok thank you very much!
Another question: so when we talk about approximately inertial systems like the earth, the Earth is said to be approximately inertial because it is rotating around the sun right ? and not because we feel the gravity, right =
 
Last edited:
nebbione said:
Ok thank you very much!
Another question: so when we talk about approximately inertial systems like the earth, the Earth is said to be approximately inertial because it is rotating around the sun right ? and not because we feel the gravity, right =

It is approximately inertial because the rotation rate of the Earth on its own axis is low. The centripetal acceleration associated with the rotation rate of the Earth (at the equator) is approximately 0.03 meters/sec^2.

If you are only quoting the acceleration of gravity to one or two significant figures, this deviation is insignificant.

If you are selling pork barbecue by the pound, this acceleration is significant. In order to be legal for use in commerce, a scale must accurately report the mass of the object being "weighed". Since a spring-based scale responds to apparent weight, this means that the calibration of the spring-based scale must reflect the centrifugal force resulting from the rotation of the Earth on its axis.
 
Thank you very much! Now i have no doubts!
 

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