Differentiating

${\displaystyle r^{n}=a^{n}\cos(n\theta )\,}$ 

and eliminating a produces a differential equation for r and θ:

${\displaystyle {\frac {dr}{d\theta }}\cos n\theta +r\sin n\theta =0.}$ 

Then

${\displaystyle \left({\frac {dr}{ds}},\ r{\frac {d\theta }{ds}}\right)\cos n\theta {\frac {ds}{d\theta }}=\left(-r\sin n\theta ,\ r\cos n\theta \right)=r\left(-\sin n\theta ,\ \cos n\theta \right)}$ 

which implies that the polar tangential angle is

${\displaystyle \psi =n\theta \pm \pi /2}$ 

and so the tangential angle is

${\displaystyle \varphi =(n+1)\theta \pm \pi /2.}$ 

(The sign here is positive if r and cos nθ have the same sign and negative otherwise.)

The unit tangent vector,

${\displaystyle \left({\frac {dr}{ds}},\ r{\frac {d\theta }{ds}}\right),}$ 

has length one, so comparing the magnitude of the vectors on each side of the above equation gives

${\displaystyle {\frac {ds}{d\theta }}=r\cos ^{-1}n\theta =a\cos ^{-1+{\tfrac {1}{n}}}n\theta .}$ 

In particular, the length of a single loop when ${\displaystyle n>0}$  is:

${\displaystyle a\int _{-{\tfrac {\pi }{2n}}}^{\tfrac {\pi }{2n}}\cos ^{-1+{\tfrac {1}{n}}}n\theta \ d\theta }$ 

The curvature is given by

${\displaystyle {\frac {d\varphi }{ds}}=(n+1){\frac {d\theta }{ds}}={\frac {n+1}{a}}\cos ^{1-{\tfrac {1}{n}}}n\theta .}$ 

The inverse of a sinusoidal spiral with respect to a circle with center at the origin is another sinusoidal spiral whose value of n is the negative of the original curve's value of n. For example, the inverse of the lemniscate of Bernoulli is a rectangular hyperbola.

The isoptic, pedal and negative pedal of a sinusoidal spiral are different sinusoidal spirals.

One path of a particle moving according to a central force proportional to a power of r is a sinusoidal spiral.

When n is an integer, and n points are arranged regularly on a circle of radius a, then the set of points so that the geometric mean of the distances from the point to the n points is a sinusoidal spiral. In this case the sinusoidal spiral is a polynomial lemniscate.

• Yates, R. C.: A Handbook on Curves and Their Properties, J. W. Edwards (1952), "Spiral" p. 213–214
• "Sinusoidal spiral" at www.2dcurves.com
• "Sinusoidal Spirals" at The MacTutor History of Mathematics
• Weisstein, Eric W. "Sinusoidal Spiral". MathWorld.