Surface of revolution
Examples of surfaces generated by a straight line are cylindrical and conical surfaces when the line is coplanar with the axis, as well as hyperboloids of one sheet when the line is skew to the axis. A circle that is rotated about its center point generates a sphere, and if the circle is rotated about a coplanar axis, not crossing the circle, then it generates a torus.
comes from the Pythagorean theorem and represents a small segment of the arc of the curve, as in the arc length formula. The quantity is the path of (the centroid of) this small segment, as required by Pappus' theorem.
Likewise, when the axis of rotation is the -axis and provided that is never negative, the area is given by
If the curve is described by the function y = f(x), a ≤ x ≤ b, then the integral becomes
for revolution around the x-axis, and
for revolution around the y-axis (Using a ≤ y ≤ b). These come from the above formula.
For example, the spherical surface with unit radius is generated by the curve x(t) = sin(t), y(t) = cos(t), when t ranges over . Its area is therefore
For the case of the spherical curve with radius , rotated about the x-axis
A minimal surface of revolution is the surface of revolution of the curve between two given points which minimizes surface area. A basic problem in the calculus of variations is finding the curve between two points that produces this minimal surface of revolution.
Rotating a function
To generate a surface of revolution out of any 2-dimensional scalar function , simply make the function's parameter, set the axis of rotation's function to simply , then use to rotate the function around the axis by setting the other two functions equal to and . For example, to rotate a function around the x-axis starting from the top of the -plane, parameterize it as for and .
Geodesics on a surface of revolution
Geodesics on a surface of revolution are governed by Clairaut's relation.
Applications of surfaces of revolution
The use of surfaces of revolution is essential in many fields in physics and engineering. When certain objects are designed digitally, revolutions like these can be used to determine surface area without the use of measuring the length and radius of the object being designed.
- Channel surface, a generalisation of a surface of revolution
- Gabriel's Horn
- Liouville surface, another generalization of a surface of revolution
- Solid of revolution
- Surface integral
- Analytic Geometry Middlemiss, Marks, and Smart. 3rd Edition Ch. 15 Surfaces and Curves, § 15-4 Surfaces of Revolution LCCN 68-15472 pp 378 ff.
- Calculus, George B. Thomas, 3rd Edition, Ch. 6 Applications of the definite integral, §§ 6.7,6.11, Area of a Surface of Revolution pp 206-209, The Theorems of Pappus, pp 217-219 LCCN 69-16407
- Singh (1993). Engineering Mathematics (6 ed.). Tata McGraw-Hill. p. 6.90. ISBN 0-07-014615-2., Chapter 6, page 6.90
- Weisstein, Eric W.. "Minimal Surface of Revolution". Mathworld. Wolfram Research. Retrieved 2012-08-29.