box rests on the back of a truck. The coefficient of static friction between box and bed of the truck is 0.390. (a) When the truck accelerates forward, what force accelerates the box

the rearrangement of particles in a physical change. hope this

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