The angular momentum exchange diagram

Just as energy and momentum are visualised with bubble diagrams, angular momentum too lends itself to a graphical representation with bubbles and arrows. Each bubble is a body, with its angular momentum in the initial state $A$ and final state $B$; the arrows represent the exchanges of angular momentum between the bodies.

Angular momentum exchange diagram: two bodies can exchange $\vec{L}$ through an internal angular impulse. If the system is isolated (no external angular impulse), $\vec{L}_\text{tot}$ is conserved.

The diagram reads immediately: the internal arrows within the system (like $I_\text{ang}$ between the two bubbles) redistribute angular momentum from one body to another but do not change the total; only the arrows that cross the boundary of the system — the external angular impulses — change $\vec{L}_\text{tot}$. When no arrow crosses the boundary, the sum of the initial angular momenta equals the sum of the final ones. It is the same accounting principle as energy diagrams, applied to rotation.

Collegamenti

Argomenti: Dinamica rotazionale Concetti: Conservazione del momento angolare Metodi: Diagramma di scambio del momento angolare

Esercizi collegati: Problema — La pattinatrice che si stringe · Esercizio svolto — proiettile contro asta incernierata · Problema — Perché il pattinatore ruota più veloce