Finding the Center of Mass of a Hemisphere

In summary, the volume of the elemental disc for calculating the center of mass of a hemisphere is given by Rd\theta (cos \theta) (\pi R^{2}cos^{2} \theta) because the arc length is measured from the \theta=0 plane (yz plane) to the plane rotated through an angle d\theta. This means the radius of the arc is the projection of R onto the \theta=0 plane, which is Rcos(\theta), and the arc length is Rcos(\theta)d\theta. To better understand this concept, a rough sketch in paint may be helpful.
  • #1
ritwik06
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Homework Statement


Center of Mass of a hemisphere

http://www.goiit.com/templates/default/images/chapters/center_mass/image064.gif
http://www.goiit.com/templates/default/images/chapters/center_mass/image068.gif
Why is volume of elemental disc = [tex]Rd\theta (cos \theta) (\pi R^{2}cos^{2} \theta)[/tex] and not

[tex]Rd\theta (\pi R^{2}cos^{2}\theta)?[/tex]
 
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  • #2
Because the arc length is measured from the [itex]\theta=0[/itex] plane (yz plane) to the plane rotated through an angle [itex]d\theta[/itex], So the radius of the arc is the projection of R onto the [itex]\theta=0[/itex] plane which is [itex]Rcos(\theta)[/itex] and so the arc length is [itex]Rcos(\theta)d\theta[/itex].
 
  • #3
gabbagabbahey said:
Because the arc length is measured from the [itex]\theta=0[/itex] plane (yz plane) to the plane rotated through an angle [itex]d\theta[/itex], So the radius of the arc is the projection of R onto the [itex]\theta=0[/itex] plane which is [itex]Rcos(\theta)[/itex] and so the arc length is [itex]Rcos(\theta)d\theta[/itex].

I don't get it. Could you please take some of ur precious time out, just to draw a very rough sketch in paint? Please!
 

FAQ: Finding the Center of Mass of a Hemisphere

What is the center of mass of a hemisphere?

The center of mass of a hemisphere is the point at which the mass of the hemisphere is evenly distributed in all directions. It is also known as the centroid or the balance point of the hemisphere.

How is the center of mass of a hemisphere calculated?

The center of mass of a hemisphere can be calculated by finding the average of all the points within the hemisphere. This can be done by dividing the hemisphere into infinitesimally small pieces and finding the average of each piece's position and mass, and then adding them all together.

What is the significance of finding the center of mass of a hemisphere?

Finding the center of mass of a hemisphere is important in various applications, including engineering, physics, and astronomy. It helps determine the stability and balance of objects, predict their motion, and understand their behavior in different environments.

How does the shape of a hemisphere affect its center of mass?

The shape of a hemisphere can affect its center of mass as it determines the distribution of mass within the object. A more symmetrical hemisphere will have its center of mass closer to its geometric center, while an irregularly shaped hemisphere will have its center of mass shifted towards the heavier side.

Can the center of mass of a hemisphere be located outside the object?

No, the center of mass of a hemisphere will always be located within the object. This is because the center of mass represents the average position of all the mass within the object, and it cannot be located outside of the object's boundaries.

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