# Weight Force

nebbione
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 ?

Mentor
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.

nebbione
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 =

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Homework Helper
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.

nebbione
Thank you very much! Now i have no doubts!