Gravitational field strength at latitude

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Discussion Overview

The discussion revolves around the concepts of gravitational field strength at different latitudes, specifically the distinction between mg0 and mgθ, and their implications for weight measurement. Participants explore the definitions and terminology used in a physics textbook regarding gravitational forces and apparent weight.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that mg0 represents the gravitational force on an object, while mgθ represents the apparent weight at latitude θ, which accounts for centripetal force.
  • There is a question about whether gθ is referred to as 'apparent gravity', with some participants agreeing with this terminology while others suggest it is also called the local value of g as a function of θ.
  • One participant expresses concern that the textbook's terminology may be incorrect, suggesting that gθ should be referred to as g0 instead.
  • Another participant defends the textbook's terminology, arguing that it combines the gravitational component with the effect of rotation, thus representing a 'net' or 'apparent' gravitational field strength.
  • Participants clarify that when measuring body weight, the reading on a balance corresponds to mgθ rather than mg0, indicating the influence of apparent weight.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the terminology used in the textbook, with some agreeing with the author's definitions while others challenge them. The discussion remains unresolved regarding the correct naming conventions for gravitational field strength at latitude.

Contextual Notes

The discussion highlights potential confusion arising from the definitions of gravitational terms and the effects of Earth's rotation, which may not be fully addressed in the textbook.

zohapmkoftid
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This figure is captured from my physics textbook and it is about the gravity at latitude

http://pix.gogobox.com.tw/out.php?i=567045_.JPG

I want to know the difference between mg0 and mg(theta). Which one is the weight of the object? Thank you!
 
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Looks to me like mg0 is the gravitational force on the object and mgθ is the apparent weight of the object at latitude θ. The apparent weight is the gravitational force minus the centripetal force. (If you hung an object from a string, the string would end up parallel to the apparent weight.)
 
Is gθ called 'apparent gravity'?
 
zohapmkoftid said:
Is gθ called 'apparent gravity'?
That's what I would call it, but it is also called the local value of g as a function of θ. It's somewhat a matter of semantics. What does your textbook call it? (What text are you using?)
 
It is a Hong Kong textbook called New Way PHYSICS for Advanced Level
In the book, gθ is called gravitational field strength at latitude θ
I think the author uses the wrong name
The gravitational field strength at latitude θ should be g0, right?

Here is the related page from my textbook
http://uploadpie.com/bHHsD
 
Last edited by a moderator:
zohapmkoftid said:
I think the author uses the wrong name
The gravitational field strength at latitude θ should be g0, right?
No, the author's terminology is reasonable. When they talk about 'gravitational field strength at latitude θ' they are lumping together the strictly gravitational component (g0) with the effect due to rotation. Think of it as the 'net' or 'apparent' gravitational field strength. (It is a bit confusing, but commonly done.)
 
gravity = g0
apparent gravity / gravity at latitude = gθ
weight = mg0
apparent weight = mgθ

I hope I don't understand wrongly

So when we measure our body weight, the reading of the balance = mgθ rather than mg0
 
zohapmkoftid said:
gravity = g0
apparent gravity / gravity at latitude = gθ
weight = mg0
apparent weight = mgθ

I hope I don't understand wrongly

So when we measure our body weight, the reading of the balance = mgθ rather than mg0
Looks good to me. (Of course, this is just a simple model of the Earth as a sphere, ignoring various complications.)
 

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