An electric current is carried by the movement of either electrons or . In a metal, the valence electrons form a(n) electron sea and are therefore free to move even in the solid state. A metal therefore conducts electricity in both the solid and the liquid state. In addition, the freely moving electron sea allows energy to be transferred readily so that metals are also good conductors of

ions, delocalized, heat

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