The two-second rule.
It is a common guideline to follow while driving.
It means that any given driver should be AT LEAST two seconds behind any vehicle that is driving in front of his vehicle. It might apply for any kind of vehicle.
Acceleration occurs whenever the forces on an object are unbalanced.
It's the group of forces on the object that's either balanced or unbalanced.
There's no such thing as "an unbalanced force".
Il existe troi types de rayons produits lors de la désintégration des éléments radioactifs:
-- "particules alpha" . . . noyaux d'hélium, composés chacun de 2 protons et 2 neutrons
-- "rayons bêta" ou "particules bêta" . . . flux d'électrons
-- "rayons gamma" . . . rayonnement électromagnétique avec les longueurs d'onde les plus courtes connues et l'énergie la plus élevée
