A modest suggestion for presenting the
loop-the-loop.
Without a CENTRIPETAL acceleration, the moving object
would follow a tangential path.
Because of the curvature of the path, the tangent
would require it to move INTO the substance of the
track.
Because the track is solid, it resists this tendency
by exerting a force ON the object in a direction OUT
of the track, ie normal to its surface at that point.
THIS force causes the path to curve (ie provides a
centripetal acceleration).
When ther curvature of the path equals the curvature
of the track, a steady state is reached and the normal
force no longer increases.