Physicists use some basic terms when they look at motion. How fast an object moves, its speed or Velocity, can be influenced by forces. (Note: Even though the terms 'speed' and 'velocity' are often used at the same time, they actually have different meanings.) Acceleration is a twist on the idea of velocity.
Expungement is the legal process by which a court removes or erases all records of a criminal conviction, even if it is a felony conviction. Your conviction will not simply disappear on its own even if you wait 10 or 20 years - you have to take action (see how long does a felony stay on your record).
If you are charged with a felony, they can wait until the six months is almost up. You will then obtain an indictment and announce ready for trial once the indictment is handed down. So in effect, they have almost six months to indict.