The conservation laws of energy and momentum are the two pillars of mechanics. The first is scalar and governs “how much” overall motion can change form; the second is vector and governs “in what direction” the system moves as a whole. Together, they allow collisions and explosions to be solved without knowing the details of the internal forces, which are often extremely violent and impossible to measure.
There is a common thread running through the whole chapter: in every spring collision, in every explosion, the same privileged velocity reappears, that of the centre of mass. It is the point that summarises the motion of the entire system, the one that moves as if all the mass were concentrated there and all the external forces acted on it. In the next chapter we shall study it directly: we shall see that the total momentum is nothing but the total mass times the velocity of the centre of mass, , and that this is the deepest formulation of its conservation.
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Topics: Quantità di moto e urti Concepts: Conservazione della quantità di moto · Centro di massa
Related exercises: Vero o falso (impulso e urti) · Urto 2D perpendicolare · Esercizio svolto — urto parzialmente anelastico