How to draw a bubble diagram

Just as the interaction diagram is used for forces, the energy-exchange diagram (or “bubble diagram”) is used for energy. It is the direct link between interactions and energy transformations: it shows at a glance which types of energy come into play, how they transform into one another, and whether the total energy of the system is conserved.

Principle — Rules for the energy-exchange diagram

1. For each body, draw a bubble for each type of energy it possesses: $E_{\text{cin}}$, $E_{\text{pot,grav}}$, $E_{\text{pot,molla}}$, $E_{\text{term}}$.
2. Inside each bubble write two numbers: the value in state A (top) and the value in state B (bottom).
3. Connect the bubbles with arrows showing the energy transfers, with the value transferred.
4. Draw the system boundary (dashed circle): internal arrows redistribute energy, arrows leaving or entering it change the total.

Bubble = type of energy. Arrow = transfer. System boundary = $E_\text{tot}$.

The fourth point is the most powerful. Drawing the system boundary sharply separates two types of arrows: internal ones, which move energy from one bubble to another without changing the total (the energy merely changes form), and those that cross the boundary, the only ones that change the overall energy of the system. If no arrow crosses the boundary — or if those that do cancel out — the total energy is conserved. The diagram thus makes the energy balance of the whole process immediately visible.

Bubble diagram: each bubble is a type of energy (with its value in A and in B). The arrows show the transfers. Only arrows crossing the system boundary change $E_\text{tot}$.

Links

Topics: Lavoro ed energia Skills: Diagramma di interazione · Bilancio energetico a bolle Methods: Diagramma a bolle di scambio energetico

Related exercises: Worked exercise — apple and spring · Problem — Kinetic energy of a ball · Problem — True or false on work and energy