compound pendulum
Also called physical pendulum.
The axis of the compound pendulum and rigid body centroid The intersection point O of the plane C and perpendicular to the rotation axis is called fulcrum Or suspension point. In the process of swing, the compound pendulum is only affected by gravity and Reaction force , but heavy moment It plays the role of restoring torque. Let the mass be m rigid body Pivoting Moment of inertia Is I, and the distance from the fulcrum to the center of mass is s, then the period of the complex pendulum's slight vibration is as shown in the figure, where g is the acceleration of gravity. It is equivalent to the pendulum length l=I/ms Simple pendulum The period of slight vibration. Take the point O 'on the extension line of OC so that OO'=l (l is the equivalent pendulum length), then this point is called the swing center of the compound pendulum. fulcrum The position can be interchanged with the swing center without changing the period of the compound pendulum. Knowing T and l, the gravitational acceleration g can be obtained from the periodic formula. When the pendulum is subjected to a impulse When it works, it will fulcrum It causes collision reaction force. If the shaft is rigid body Fulcrum inertia Spindle, outer impulse If the line OC perpendicular to the fulcrum and the center of mass acts on the swing center O ', the collision reaction force on the fulcrum is zero. Therefore, the swing center of the compound pendulum is also called the impact center. There are some rotating parts in the machine that must withstand collision, such as clutches, impact pendulums, etc. In order to prevent the damage of huge instantaneous forces to bearings, the impact force of collision should pass through the impact center. 
