The link between the interaction diagram and the bubble diagram is direct, and this is what makes the method so effective: there’s no need to guess which energies to draw, because the interaction diagram dictates them. Every wiggly line in the interaction diagram that admits potential energy generates a potential-energy bubble in the bubble diagram. Wiggly lines without potential energy (friction, constraint) generate no bubble at all, but instead direct transfers (arrows) between and , or between the kinetic energies of two bodies.
The operating rule is therefore simple: look at each interaction already identified in the interaction diagram and “translate” it. If the interaction is conservative (weight, spring, Coulomb), a new potential-energy bubble appears, connected to the body’s kinetic energy by the work of the force. If the interaction is dissipative or a constraint, no reservoir is born: only the arrow that carries the energy to where it ends up is drawn.
From the interaction diagram to the bubble diagram: the “weight” wiggly line (which admits ) becomes an bubble. The transfer from to is the work of gravity.
The example of the falling ball shows the mechanism in its purest form. In the interaction diagram there’s a single wiggly line, the weight, linking the ball to the Earth. Since weight is conservative, this wiggly line translates into a gravitational potential-energy bubble . The work of gravity is the arrow that transfers energy from this bubble to the kinetic one: as the ball falls, decreases and grows by the same amount. No arrow crosses the boundary of the system, so total energy is conserved, and this is immediately written as .
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Topics: Lavoro ed energia Skills: Diagramma di interazione Methods: Diagramma a bolle di scambio energetico
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