When talking about Acceleration ,what is significant about the about the sign(+ or -)?

Acceleration at its most basic is the act of increasing your running speed. From a standing start (or blocks), you explode into action. If you’re already running, you pick up the pace. Acceleration continues until you can no longer increase your speed, at which point you achieve maximum velocity (top-end speed). Acceleration seems simple enough. The plus means your increasing speed, the k=minus means your decreasing in speed.

Explanation:

this is an example of "committed" time.

committed time, as contracted time, takes need over essential and available time since it is seen as profitable work. it alludes to the time allotted to keep up a home and family. at the point when a man is commuting using committed time this individual may feel that the drive is an obligation to family, for example, strolling youngsters to class or driving a mate to work. contracted and committed time clients may feel that their commute could really compare to the commute of important or leisure time clients on the grounds that their commute is profitable work. in this manner, they might be more disposed to pick a mechanized method of movement.  

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