¿Qué es la unidad derivada?

Explanation:

Las unidades derivadas son la combinación de unidades base para expresar una cantidad física. ... La combinación contendrá unidades base en forma multiplicada o dividida. Por ejemplo, la velocidad es la distancia recorrida por unidad de tiempo, es decir, por lo tanto, la unidad derivada de la velocidad es 'm/s'.

estoy estudiando español en mi escuela

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me