Where is the Center of Mass in a Solid Hemisphere?

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SUMMARY

The center of mass of a solid hemisphere with uniform density and radius R is located between the points 0 and R/2 along the z-axis. The discussion clarifies that the center of mass cannot be exactly at R/2 due to the distribution of mass, which results in more mass being below that point. Participants emphasized the importance of understanding the concept of center of mass as the average of mass positions rather than relying on visual estimations. The conversation also highlighted the need for analytical reasoning over direct answers in homework forums.

PREREQUISITES
  • Understanding of center of mass concepts
  • Familiarity with solid geometry, specifically hemispheres
  • Basic knowledge of uniform density and mass distribution
  • Ability to visualize 3D objects and their properties
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  • Study the derivation of the center of mass for various geometric shapes
  • Learn about the integration techniques used in calculating center of mass
  • Explore the implications of mass distribution on center of mass location
  • Review examples of center of mass calculations in physics problems
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Westin
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Homework Statement


Consider a solid hemisphere of uniform density with radius R. Where is the center of mass?

z=0
0
char3C.png
z
char3C.png
R
char3D.png
2
z=R
char3D.png
2
R
char3D.png
2
char3C.png
z
char3C.png
r
z=R

Image is provided.

Homework Equations

None

The Attempt at a Solution



Answer A and E do not seem logical. I thought it was answer C from my eyes. Center of mass is the average of the masses factored by their distances from a reference point. I didn't think the answer could range like B and D do.[/B]
 

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Westin said:

Homework Equations

None
Really? No equation for the center of mass?

Westin said:
Answer A and E do not seem logical. I thought it was answer C from my eyes. Center of mass is the average of the masses factored by their distances from a reference point. I didn't think the answer could range like B and D do.
Do you understand that the range is there to keep you from having to calculate the exact value? It doesn't mean that the center of mass can be anywhere within that range.
 
If the center of mass were precisely at R/2, there will be more mass below than above that point. Hence, it must be somewhere between R/2 and...
 
NTW said:
If the center of mass were precisely at R/2, there will be more mass below than above that point.
I don't understand what you mean.
 
DrClaude said:
I don't understand what you mean.
To make a mental experiment: If I imagine a given point on the Z axis, precisely at R/2, and also imagine the hemisphere as formed by a very large, but finite number of particles, the number of particles with z-coordinates lower than R/2 will be larger than the number of particles with z-coordinates higher than R/2. Hence, in order to reach a 50% partition in the values of the z-coordinates, that point must be placed somewhere between 0 and R/2.
 
NTW said:
If I imagine a given point on the Z axis, precisely at R/2
Ok, but that's not the same as saying "if the center of mass were precisely at R/2."

Also, please to not give direct answers in the homework forums. The poster has to do the work.
 

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