Disk And Washer Method Math
And similarly the volume of the object generated by revolving a function g y about the line x k from y c to y d is given by.
Disk and washer method math. You can think of the main difference between these two methods being that the washer method deals with a solid with a piece of it taken out. Where r is the outer radius the big radius and r is the radius of the hole the little radius. Volume disk washer method. V π r 2 h π f x 2 dx.
The volume of the object generated by revolving a function f x about the line y k from x a to x b is given by. V b a a x dx v d c a y dy v a b a x d x v c d a y d y. R 2 h 2 h therefore the volume of this spherical segment would be. Where a x a x and a y a y is the cross sectional area of the solid.
The area of the circle minus the hole is. There are many ways to get the cross sectional area and we ll see two or three depending on how you look at it over the next two sections. The washer method for finding the volume of a solid is very similar to the disk method with one small added complexity. And that is our formula for solids of revolution by disks.
A π r 2. And the volume is found by summing all those disks using integration. The height of the disk is equal to dx think of the disk as a cylinder standing on edge. Therefore the volume of a single cylindrical disk is.
And the radius r is the value of the function at that point f x so. This is the currently selected item. A π f x 2. So let s jump into an example and i ll explain the difference as we go.
Washer method rotating around horizontal line not x axis part 2. Add up the volumes of the washers from 0 to 1 by integrating. V 4 π r 2 r 2 h 2 r 2 h 2 3 2 3 h 4 r 2 h 2 0 r 2 h 2 2 h 2 r 2 x 2 d x 0 r 2 h 2 2 h 2 r 2 x 2 d x h 3 r 2 h 2 r 2 tan 1. Exactly as you would expect from the name a washer is just a disk with a hole taken out of its center.
You can always use either the difference is that the washer method takes the cross section of your final shape then rotates it while the disk method subtracts the entire volume of the shape enclosed by g x from the shape enclosed by f x. π f x 2 dx. Multiply this area by the thickness dx to get the volume of a representative washer. Disc washer methods challenge.