: Mmmkay but say a car is backing, after 1 sec it has travelled 1 metres, after
: 2 secs it has travelled 3 metres, then it must have been acc elerating,
: right? Even though it's speed was negative (it was moving backwards) its
: velocity per second was incrasing, so it must have been accelerating!
Depends on when you're talking about acceleration and velocity as magnitudes or vectors. A vector cannot be negative (-v = v pointing in the opposite direction). However, in 1D motion problems like this one, it's usually much easier/simpler to use magnitudes, so I would say that the car does have a negative acceleration. Look at it this way, the value of the acceleration is the same as it would be if the car was going forward and "decelerating" (I've never heard the term deceleration used in real physics since a negative acceleration is allowed).
Wonder if SiliconDream is still around here, this is his territory :P
