How to find the center of mass of a cube?

In summary, to solve for the center of mass of a homogeneous solid cube in three dimensions, you would use the same calculations as you would in two dimensions, but with the cube lying in the first octant of the space (all three coordinates positive), and with each edge of the cube parallel to one of the three axes.
  • #1
Davidllerenav
424
14

Homework Statement


Find the center of mass of a homogeneous solid cube with side ##L## analytically.

Homework Equations


None.

The Attempt at a Solution


I don't understand how to find the center of mass on three dimensions. I know that since it is homogeneous, if I center the cube on the origin, then the center of mass would be on ##(0,0,0)##, but how do I find this analytically?
 
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  • #2
How would you do it in two dimensions? If you think about the technique you use in that case, it should become apparent how you might extend that to three dimensions.
 
  • #3
andrewkirk said:
How would you do it in two dimensions? If you think about the technique you use in that case, it should become apparent how you might extend that to three dimensions.
In two dimensions I would no center it at the origin, I use ##(0,0)## as one of the corners of the square, then I would find the ##x## component by ##X_{cm}=\frac{\int\sigma x dA}{\int\sigma dA}## and the ##y## component by ##Y_{cm}=\frac{\int\sigma y dA}{\int\sigma dA}##. So ##X_{cm}=\frac{\int_{0}^L Lxdx }{\int_{0}^L Ldx}=\frac{L\int_{0}^L xdx}{L\int_{0}^L dx}=\frac{\frac{x^2}{2}}{L}=\frac{L}{2}##, the same would be for ##y##, so ##Y_{cm}=\frac{\int_{0}^L Lydy }{\int_{0}^L Ldy}=\frac{L\int_{0}^L ydy}{L\int_{0}^L dy}=\frac{\frac{y^2}{2}}{L}=\frac{L}{2}##, so the center of mass would be on the point ##\left(\frac{L}{2},\frac{L}{2}\right)##. How should I do this with three dimensions?
 
  • #4
Just do the same calculation for the z dimension as you did for the x and y dimensions, using (0,0,0) as one of the corners of the cube, the cube lying entirely in the first octant of the space (all three coordinates positive) and with each edge of the cube parallel to one of the three axes.
 
  • #5
andrewkirk said:
Just do the same calculation for the z dimension as you did for the x and y dimensions, using (0,0,0) as one of the corners of the cube, the cube lying entirely in the first octant of the space (all three coordinates positive) and with each edge of the cube parallel to one of the three axes.
So I would end up with ##L/2## again? Would be something like ##Z_{cm}=\frac{\int_{0}^L Lzdz }{\int_{0}^L Ldz}=\frac{L\int_{0}^L ydz}{L\int_{0}^L dz}=\frac{\frac{z^2}{2}}{L}=\frac{L}{2}##? Or would something change?
 
  • #6
Davidllerenav said:
So I would end up with ##L/2## again? Would be something like ##Z_{cm}=\frac{\int_{0}^L Lzdz }{\int_{0}^L Ldz}=\frac{L\int_{0}^L ydz}{L\int_{0}^L dz}=\frac{\frac{z^2}{2}}{L}=\frac{L}{2}##? Or would something change?
Yes, you'd end up with that. Nothing would change.
 
  • #7
andrewkirk said:
Yes, you'd end up with that. Nothing would change.
Ok. Then the aswer would be just to write thos three calculations and that's it?
 

1. How do you determine the center of mass of a cube?

The center of mass of a cube can be found by identifying the midpoint of each side and then connecting these points to form the diagonals of the cube. The intersection of these diagonals is the center of mass.

2. What is the formula for calculating the center of mass of a cube?

The formula for finding the center of mass of a cube is (a/2, a/2, a/2), where a is the length of one side of the cube. This means that the center of mass is located at the midpoint of each side of the cube.

3. Can the center of mass of a cube be outside the cube?

No, the center of mass of a cube will always be located within the boundaries of the cube. This is because the center of mass is determined by the distribution of mass within an object.

4. How does the distribution of mass affect the center of mass of a cube?

The center of mass of a cube is directly influenced by the distribution of mass within the cube. If the mass is evenly distributed, the center of mass will be at the geometric center of the cube. However, if the mass is unevenly distributed, the center of mass will shift towards the side with the higher amount of mass.

5. Is finding the center of mass of a cube important in physics?

Yes, determining the center of mass of an object is crucial in physics as it helps in understanding the motion and stability of an object. It also plays a role in calculating the moment of inertia and torque of a cube, which are important concepts in physics.

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