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A compound pendulum (or physical pendulum) is one where the rod is not massless, and may have extended size; that is, an arbitrarily shaped rigid body swinging by a pivot . In this case the pendulum's period depends on its moment of inertia I O {\displaystyle I_{O}} around the pivot point.
The moment of inertia of the compound pendulum is now obtained by adding the moment of inertia of the rod and the disc around the pivot point as, =, + +, + (+), where is the length of the pendulum. Notice that the parallel axis theorem is used to shift the moment of inertia from the center of mass to the pivot point of the pendulum.
The moments of inertia of a mass have units of dimension ML 2 ([mass] × [length] 2). It should not be confused with the second moment of area, which has units of dimension L 4 ([length] 4) and is used in beam calculations. The mass moment of inertia is often also known as the rotational inertia, and sometimes as the angular mass.
The pendulum carries an amount of air with it as it swings, and the mass of this air increases the inertia of the pendulum, again reducing the acceleration and increasing the period. This depends on both its density and shape. Viscous air resistance slows the pendulum's velocity. This has a negligible effect on the period, but dissipates energy ...
The pendulum is usually adjusted by moving the moment of inertia adjustment weights towards or away from the centre of the mass by equal amounts on each side in order to modify f R, until the rotational frequency is close to the translational frequency, so the alternation period will be slow enough to allow the change between the two modes to ...
where is the moment of inertia around the CM. For any point P a distance p {\displaystyle p} on the opposite side of the CM from the point of impact, the change in velocity of point P is: d v n e t = d v c m − p d ω . {\displaystyle dv_{net}=dv_{cm}-pd\omega .}
It is similar to a block diagram or signal-flow graph, with the major difference that the arcs in bond graphs represent bi-directional exchange of physical energy, while those in block diagrams and signal-flow graphs represent uni-directional flow of information. Bond graphs are multi-energy domain (e.g. mechanical, electrical, hydraulic, etc ...
Cavendish's diagram of his torsion pendulum, seen from above. The pendulum consists of two small spherical lead weights (h, h) hanging from a 6-foot horizontal wooden beam supported in the center by a fine torsion wire.