Glossary
Axis of Rotation
The line around which a two-dimensional region is revolved to create a three-dimensional solid.
Example:
If you're rotating a region around the line , then is your axis of rotation.
Disc Method
A calculus technique used to find the volume of a solid of revolution when the region being rotated extends directly to the axis of rotation, forming solid circular cross-sections.
Example:
To find the volume of a solid sphere, you could use the Disc Method by rotating a semicircle around the x-axis.
Inner Radius ($g(x)$)
In the Washer Method, this is the function that is nearer to the axis of rotation within the specified interval, determining the smaller radius of the washer.
Example:
When revolving the region between and around the x-axis for , would be the inner radius function as it is closer to the x-axis.
Intersection Points
The coordinates where two or more functions meet, often used to determine the upper and lower bounds for integration in volume problems.
Example:
To set up the integral for the volume between and , you first need to find their intersection points at and .
Lower Bound (c)
The starting x- or y-value that defines the beginning of the region being rotated, serving as the lower limit of integration.
Example:
If a region is bounded by and , then is the lower bound for your integral.
Outer Radius ($f(x)$)
In the Washer Method, this is the function that is farther from the axis of rotation within the specified interval, determining the larger radius of the washer.
Example:
When revolving the region between and around the x-axis for , would be the outer radius function because it is farther from the x-axis.
Upper Bound (d)
The ending x- or y-value that defines the end of the region being rotated, serving as the upper limit of integration.
Example:
If a region is bounded by and , then is the upper bound for your integral.
Volume of a Solid of Revolution
The three-dimensional space occupied by a solid formed by rotating a two-dimensional region around an axis.
Example:
Calculating the volume of a solid of revolution can help engineers determine the capacity of a cylindrical tank or the material needed for a specific part.
Washer (geometric shape)
A two-dimensional shape resembling a flat ring, formed by a larger circle with a smaller concentric circle removed from its center.
Example:
When you slice through a solid generated by the Washer Method, each cross-section will look like a washer.
Washer Method
A calculus technique used to find the volume of a solid of revolution when the region being rotated has a hole in the middle, formed by revolving the area between two functions around an axis.
Example:
To calculate the volume of a solid shaped like a ring or a thick pipe, you would apply the Washer Method by rotating the area between two curves.