Bubble diagram for collisions

For collisions the bubble diagram shows at a glance what happens to the energy. Each bubble is a reservoir of one type of energy, with its value before (top) and after (bottom); the arrows are the transfers.

Comparison: in the elastic collision all the energy stays kinetic (it only moves from one body to the other); in the inelastic collision part of it slips into the thermal-energy bubble and never comes back.

The visual difference is stark. In the elastic collision only kinetic-energy bubbles appear: energy pours from one body into the other, but the sum $E_\text{cin,tot}$ stays identical. In the inelastic collision a new bubble lights up, that of thermal energy $E_\text{term}$: an arrow leaves the kinetic bubbles and ends up there, and from that bubble the energy never goes back to being motion. Momentum, meanwhile, is conserved in both cases: the bubbles only tell the story of energy, not that of $\vv{p}$.

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Topics: Quantità di moto e urti Concepts: Urto elastico · Urto anelastico · Energia cinetica Skills: Bilancio energetico a bolle

Related exercises: Urto elastico tra due biglie · Vero o falso sugli urti · Pendolo balistico (altezza)