The four resistances are R1 = 1 , R2 = 2 , R3 = 4 , and R4 = 12. The power source has a potential difference V = 12 V. (a) Find the equivalent resistance of the circuit. (b) What is the value of the current I in the circuit? (c) Find the currents in R3 and R4.

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