# Surface of screw motion

From Encyclopedia of Mathematics

*helical surface*

A surface described by a plane curve $L$ which, while rotating around an axis at a uniform rate, also advances along that axis at a uniform rate. If $L$ is located in the plane of the axis of rotation $z$ and is defined by the equation $z=f(u)$, the position vector of the surface of screw motion is

$$r=\{u\cos v,u\sin v,f(u)+hv\},\quad h=\text{const},$$

and its line element is

$$ds^2=(1+f'^2)du^2+2hf'dudv+(u^2+h^2)dv^2.$$

A surface of screw motion can be deformed into a rotation surface so that the generating helical lines are parallel (Boor's theorem). If $f=\text{const}$, one has a helicoid; if $h=0$, one has a rotation surface, or surface of revolution.

#### References

[a1] | M. Berger, B. Gostiaux, "Differential geometry: manifolds, curves, and surfaces" , Springer (1988) (Translated from French) |

[a2] | H.S.M. Coxeter, "Introduction to geometry" , Wiley (1961) |

[a3] | M.P. Do Carmo, "Differential geometry of curves and surfaces" , Prentice-Hall (1976) pp. 145 |

**How to Cite This Entry:**

Surface of screw motion.

*Encyclopedia of Mathematics.*URL: http://encyclopediaofmath.org/index.php?title=Surface_of_screw_motion&oldid=55581

This article was adapted from an original article by I.Kh. Sabitov (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article