On the circumference of the upper disk, the trilinear pendulum is symmetrically connected to the vertex of the regular triangle at the edge of the larger uniform disk below along the vertex of the equilateral triangle. When the three horizontal lines of the upper and lower plates are equal in length, the upper coil rotates by a small angle with the vertical central axis O 1O, and the suspended great circle twists around the central axis O 1O with the help of the tension of the suspension line.

Mass moment of inertia

Its size depends on the shape, mass distribution and the position of the rotating shaft of the object. The moment of inertia of rigid body has important physical significance, and it is also an important parameter in scientific experiments, engineering technology, aerospace, electric power, machinery, instrumentation and other industrial fields. Because of the different moments of inertia of coils, the indicating system of electromagnetic instruments can be used to measure micro-current (galvanometer) or electric quantity (pulse galvanometer) respectively. In the shape design of engine blades, flywheels, gyroscopes and artificial satellites, it is necessary to accurately measure the moment of inertia.