# Write a triple integral in cylindrical coordinates for the volume

So, I get the symmetric thing. The equation of a sphere centered at the origin is x squared plus y squared plus z squared equals radius squared. OK, so there is a special case where, so, x bar is one over the mass times triple integral of x density dV. The mass is given by the triple integral: OK, so now we have actually a name for this because we're doing it in space.

But, so the center of mass of a solid is just given by taking the average values of x, y, and z. But hopefully you've seen how to do that. OK, so that's why they are called cylindrical coordinates. So, well actually, let's not. So, if you look at the picture just, say, in the yz plane, you get this point and that point. So, that will be z. So, the unit ball is just, you know, well, stay inside of the unit sphere. OK, so the average value of the function f of x, y, z in the region, r, that would be f bar, would be one over the volume of the region times the triple integral of f dV.

And, it tells you how hard it is to actually spin that top. To change to cylindrical coordinates from rectangular coordinates use the conversion: The mass is given by where R is the region in the xyz space occupied by the solid.

Well, the reason is if I give you x and y, then you can find quickly, what's the bottom and top values of z for that choice of x and y.

The first octant is the octant in which all three of the coordinates are positive. I still have dV. Yeah, it's going to be a circle because entire picture is invariant by rotation about the z axis.

Spherical coordinates We integrate over regions in spherical coordinates. Just as the two-dimensional coordinates system can be divided into four quadrants the three-dimensional coordinate system can be divided into eight octants.

And, we've seen that. And, if you solve for y, given x, you get plus minus root of two minus x squared, OK. Now, I know that you can imagine how to actually do this one as a double integral. Divergence theorem We introduce the divergence theorem.

OK, so the small mass element, maybe I should have written that as dm, the mass element, is density times dV.

So, it depends on what symmetry you use, if you use symmetry between top and bottom you'd say, well, the volume is twice the lower half.

But, this one is pointing down, and when you take x equals y equals zero, you get z equals four. And, there's one more step. So, the condition is that, sorry, the plane is below the sphere. So then, for a given value of x and y, I claim z goes from the bottom surface. Here is a sketch of the first possibility. Here is a sketch of the plane in the first octant. CALCULUS Understanding Its Concepts and Methods. Home Contents Index. Triple integrals, Cylindrical coordinates. The differential of volume in cylindrical coordinates is given by. A cylindrical tube of radius cm and length cm contains a gas. Since the tube is spinning around its axis, the density of the gas increases with its distance from the axis. The density, at a distance of cm from the axis is gm/cc. (a) Write a triple integral representing the total mass of the gas in the tube. Triple integrals are more difficult (in fact, usually impossible) to picture than double integrals, but the principle is much the same.

Use a triple integral to find the volume of the prism \(D\) in the first octant bounded by the planes \(y=x\) and \(z=6\). Solution. Note that this prism is Triple Integrals in Cylindrical Coordinates. Triple Integrals in Spherical Coordinates Another approach to evaluating triple integrals, that is especially useful when integrating over regions that are at least partially de ned using spheres, is to use spherical coordinates.

Example 1. Suppose we want to evaluate. where is the solid enclosed by the planes and and the cylinders We can use the cylindrical coordinates as. We see that the bottom of the given long washer is a region between to circles and so and We write. Example 2. Suppose we want to evaluate. Cylindrical Coordinates Find the volume of a cylinder using cylindrical coordinates.

Set up the integral at least three di erent ways, and give a geometric interpretation of each ordering. Write a triple integral in cylindrical coordinates for the volume
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