
trochoid


The curve traced out by a fixed point on the radius or its extension of a circle as the circle rolls along a straight line. The curve is also given the name:
 curtate cycloid if the fixed point is inside the circumference;
 cycloid if the fixed point is on the circumference;
 prolate cycloid if the fixed point is outside the circumference.
However, there is no consistency about the usage of these terms.

