Calyx of some species of clematis and of some herbaceous plants, or rolled up at the edges (involute or revolute), or folded transversely, becoming crumpled or corrugated, as in the poppy.
U=cv~-+-a To apply this to involute teeth, let ci be the length of the approach, c2 that of the recess, u1, the mean volocity of sliding during the approach, u2 that during the recess; then civil i\ c,v/1 I
Which, substituted in equation (63), gives the work lost in a unit of time by th~ friction of involute teeth.
This result, which is exact for involute teeth, is approximately true for teeth of any figure.
~s Now, suppose a tracing point T Pa to be fixed to the cord, so as to be carried along the path of con- Dz a tact P11P2, that point will trace on a plane rotating along with the wheel I part of the involute of the base-circle DfD1, and on a plane rotating along with the wheel 2