Trochoid
A trochoid is traced by a fixed point a distance d from the center of a circle of radius r as it rolls along a straight line. Use the sliders to adjust the radius r of the circle and the distance d of the point to the center of the circle. Note the type of curve when d>r, d=r, and d<r. The case where d=r is called a cycloid. If d<r it is called a curtate cycloid and if d>r it is called a prolate cycloid.
Move the slider to adjust the value of t to see the curve traced out - you can also click the play button in the lower left to animate.
To change the viewing window, hold the shift button and left-click to drag the graph or use the scroll wheel to zoom in/out. You can also adjust the axes by holding the shift button and left-click on the axis you want to change.