☰ button brings up a control panel
Animation shows projection of given motion on to a moving surface.
The position of a moving body is projected on to the surface moving to the right at constant speed behind/below the moving body. This should be the position relative to the surface and the line joining these positions is the path relative to surface. (An observer moving along with the surface imagines himself to be at rest and would imagine a leftward motion for the object added to it's motion as seen by the ground observer.)
In SHM example the block is released from a stretched position of the spring and performs vertical oscillations. As the mass moves up and down the positions are projected on to the moving surface behind it.
In circular motion example the body can be imagined to perform uniform circular motion in a horizontal plane and the moving surface is below it.
In the falling body example, the body starts falling freely as the string connecting it to the support breaks. The moving surface is vertical and behind the freely falling body.
Observe the spacing between the dots marking the positions of the body relative to the surface. The dots are marked at equal intervals of time.