Outer radius

Definition

The outer radius refers to the distance from the axis of rotation to the outer edge of a solid when calculating volumes of revolution using cylindrical shells. This term is crucial for determining how much 'space' the shell occupies, influencing the overall volume generated when a region is revolved around an axis. Understanding the outer radius helps in setting up the integral that computes the volume.

5 Must Know Facts For Your Next Test

1. The outer radius is often expressed as a function of the variable in the integral when calculating volume using cylindrical shells.
2. To find the outer radius, identify the farthest distance from the axis of rotation to the curve being revolved.
3. The formula for the volume of a cylindrical shell involves both the outer radius and the height of the shell.
4. When rotating around the y-axis, the outer radius is typically a function of x, while height may be expressed in terms of y.
5. Understanding how to correctly identify and apply the outer radius is essential for accurately setting up integrals for volume calculations.

Review Questions

• How does identifying the outer radius impact setting up an integral for volume calculation using cylindrical shells?
  • Identifying the outer radius is essential because it determines how far each shell extends from the axis of rotation. This directly influences the dimensions used in the integral, particularly in defining the limits and integrating with respect to the correct variable. Without correctly determining this distance, you would miscalculate both the height and overall volume, leading to inaccurate results.
• What role does the outer radius play in distinguishing between inner and outer shells when using cylindrical shells for volume calculation?
  • The outer radius specifically helps differentiate between inner and outer shells during volume calculations. The outer shells are those that are farther from the axis of rotation, while inner shells are closer. This distinction is crucial because it affects how each shell's volume contributes to the overall volume being calculated, as you must integrate different expressions based on their respective radii.
• Evaluate how changing the axis of rotation alters how we calculate the outer radius and affects our final volume result.
  • Changing the axis of rotation fundamentally alters how we measure distances for both inner and outer radii. For instance, if we switch from rotating around the x-axis to rotating around the y-axis, we must redefine our variables and potentially shift our functions. This re-evaluation impacts our setup for integrals, as distances will change according to which axis we are measuring from. As a result, these changes can lead to significantly different final volume calculations if not properly accounted for.

Related terms

cylindrical shells: Cylindrical shells are thin, hollow cylinders used in calculus to approximate the volume of solids formed by rotating a region around an axis.

axis of rotation:

The axis of rotation is the line about which a figure is rotated to form a solid, affecting how distances, including the outer radius, are measured.

volume of revolution: Volume of revolution is the volume of a three-dimensional object created by rotating a two-dimensional shape around an axis.