A penis erection demonstration model including a motor driving a gear assembly, a cam driven by a gear of the gear assembly, a plunger extending from the cam, and an elastic arm extending from a casing of the demonstration model and encasing the plunger. Rotation of the motor in a first direction causes the plunger to extend into the arm a first distance depicting a flaccid state and rotation of the motor in a second direction causes the plunger to extend into the arm a second distance depicting an erect state.