What Is a Hollow Cylinder?
A hollow cylinder (also called a cylindrical shell, tube, or pipe) is a three-dimensional shape formed by two coaxial cylinders. It has an outer radius R and an inner radius r, with the material filling the space between them. Common examples include pipes, tubes, drinking straws, rings, and bushings.
Hollow Cylinder Formulas
Volume
The volume of material in the hollow cylinder.
Cross-Section Area
The annular (ring) area of the cross-section.
Wall Thickness
The thickness of the wall material.
Total Surface Area
Outer + inner lateral surfaces + two annular ends.
Outer Lateral Area
The outer curved surface area.
Inner Lateral Area
The inner curved surface area.
Understanding the Volume Formula
The volume of a hollow cylinder can be understood as the difference between the volume of the outer solid cylinder and the inner hollow space:
V = V_outer - V_inner = pi x R^2 x h - pi x r^2 x h = pi x h x (R^2 - r^2)
This can also be factored as: V = pi x h x (R + r)(R - r), which shows that the volume depends on both the average radius and the wall thickness.
Practical Applications
- Plumbing: Calculating the volume of pipe material for weight and cost estimation
- Engineering: Determining material volumes for cylindrical bushings, bearings, and sleeves
- Manufacturing: Computing the volume of hollow tubes for extrusion and casting processes
- Fluid dynamics: Calculating the volume of fluid that can fill a pipe (inner volume)
- Construction: Estimating concrete needed for cylindrical columns with hollow cores
Step-by-Step Example
Find the volume of a hollow cylinder with outer radius R = 10, inner radius r = 7, and height h = 15:
- Calculate R^2 - r^2 = 100 - 49 = 51
- Multiply by pi: pi x 51 = 160.2212
- Multiply by height: V = 160.2212 x 15 = 2403.318
- Wall thickness: t = 10 - 7 = 3