Boundaries

[Title: Boundaries] [Verse 1 — Male] Before you write a single law You have to draw the line What crosses in, what crosses out Defines the system every time Matter, energy, both, or neither The boundary is your choice Get it wrong and the math falls apart Get it right and the model works [Chorus — Female] Open lets it all come through Matter, energy, moving free Closed holds matter, lets heat pass Isolated, nothing leaves [Verse 2 — Male] A living cell is open wide Mass and energy flow in and out A sealed piston traps the gas But heat can move, no doubt A perfect thermos, locked up tight No exchange with anything That is the ideal isolated case No heat, no work, no mass crossing [Bridge — Male + Female] The boundary is not the object It is the choice you make Draw it wide or draw it narrow Watch what the equations take [Final Chorus — Female + Male harmony] Open lets it all come through Matter, energy, moving free Closed holds matter, lets heat pass Isolated, nothing leaves [Outro — Both] Three types, one question underneath What does the system share Master the boundary, master the math Everything else follows from there