How to find centre of gravity for a hemisphere shell?

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Discussion Overview

The discussion revolves around the calculation of the center of gravity for a hemisphere shell, with participants seeking methods and clarifications related to this topic. The scope includes theoretical approaches and mathematical reasoning relevant to the problem.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Homework-related, Mathematical reasoning

Main Points Raised

  • One participant requests assistance in calculating the center of gravity for a hemisphere shell, indicating a need for problem-solving support.
  • Another participant suggests integrating mass density over the surface in different axial directions, providing a formula for calculating the center of mass (COM) in rectangular coordinates, though they express uncertainty about their memory.
  • A different participant proposes using symmetry arguments related to rotation around the Oz axis to simplify the problem to finding the center of mass for a semicircle of radius R, focusing on the z-coordinate for the hemisphere.
  • Concerns are raised about discrepancies between results obtained from integration and symmetry arguments, specifically noting that the center of mass for a semicircular wire differs from that of the hemisphere when calculated through these methods.
  • A later reply indicates that the original poster is not alone in struggling with this problem, suggesting ongoing confusion or difficulty in understanding the concepts involved.

Areas of Agreement / Disagreement

Participants express differing views on the methods for calculating the center of gravity, with no consensus reached regarding the validity of the integration versus symmetry arguments. The discussion remains unresolved as participants highlight conflicting results.

Contextual Notes

There are unresolved mathematical steps and potential dependencies on definitions related to the center of mass calculations. The discussion reflects varying levels of understanding and uncertainty among participants.

Who May Find This Useful

This discussion may be of interest to students preparing for examinations in physics or engineering, as well as those exploring concepts related to center of gravity and mass distribution in geometrical shapes.

mick_1
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How to find centre of gravity for a hemisphere shell??

Can someone show me how to calculate centre of gravity for a hemisphere shell??
 
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These sound suspiciously like homework problems.
 
It's not homework, I'm preparing for an examination. And I have serious problem solving this assignment. Pleas help me!
 
Integrate mass density over the surface for each axial direction. As far as I can remember for rectangular coordinates its

[tex]y_{cm} = \int{\rho(x) f(x)dx}[/tex]

[tex]x_{cm} = \int{\rho(x) xf(x)dx}[/tex]

but my memory is probably mistaking me. There should be an example of this in your book though.
 
Here's the hint:use the rotation around Oz symmetry to transform your problem into a very simple one:finding the C of M for a semicircle of radius R.You basically need the "z" coordinate of the C of M for the hemisphere,or the "y" coordinate for the C of M for the semicircle.

Daniel.
 


The result obtained from integration and your symmetry argument are NOT the same.
For a semicircular wire, the COM is [tex](0, \frac{2R}{\pi})[/tex] while from integration, it is [tex](0,0,R/2)[/tex]. Can anybody explain this?
 


I know this is an old post, but I have been struggling with the same problem for a while now , can anyone explain this?
 

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