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Re: Physics people...
Posted By: Steve LevinsonDate: 6/13/02 11:04 a.m.

In Response To: Re: Physics people... (Mark Levin)

: Wonder if SiliconDream is still around here, this is his territory :P

It's mine, too. OK, I'm not a physicist, but my Engineering background probably qualifies me here. Mark's answer is essentially correct. Velocity and acceleration are vectors - they have a magnitude and a direction. The magnitude can never be negative. In the realm of true physics, there really is no such thing as deceleration. From a practical standpoint, however, deceleration refers to a velocity magnitude that is decreasing with time. Not a velocity vector. So if a car is moving backwards and the magnitude of the backwards velocity is increasing (it's going faster and faster), even though it is moving in a negative direction, it is still accelerating. Similarly, think of a book falling to the floor. Let's say that the origin is the center of the Earth. The book is then moving in a negarive direction, but it's moving faster and faster - it is accelerating toward the center of the earth.

Another way to think of this is that acceleration results whenever the velocity and acceleration vectors are in the same direction, and deceleration occurs when they are in opposite directions. Yes, I realize that this doesn't work when velocity is zero, but you get the idea. Obviously, for anything more than a 1-D problem, the concept of deceleration is ambiguous. For example, a car that is making a turn is accelerating in one direction and decelerating in another. From the standpoint of magnitudes of vectors, there may be no change at all, but simply going around a curve results in an angular acceleration component - and that's another, very long story.

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Replies:

Physics people...Vid Boi 6/13/02 8:08 a.m.
     Re: Physics people...Tru7h 6/13/02 8:35 a.m.
           Re: Physics people...Vid Boi 6/13/02 9:32 a.m.
                 Re: Physics people...Mazilurik 6/13/02 10:28 a.m.
                 Re: Physics people...Mark Levin 6/13/02 10:31 a.m.
                       Re: Physics people...Steve Levinson 6/13/02 11:04 a.m.
                             Re: Physics people...Vid Boi 6/13/02 5:21 p.m.
                 Re: Physics people...Tru7h 6/13/02 2:27 p.m.
     Re: Physics people...spacemonkey 6/13/02 11:18 a.m.
     Acceleration defined in 3 words.Djof 6/13/02 11:39 a.m.
           Re: Acceleration defined in 3 words.Scott Noblitt 6/13/02 6:38 p.m.
                 Re: Acceleration defined in 3 words.Djof 6/13/02 8:35 p.m.
                       Re: Acceleration defined in 3 words.Scott Noblitt 6/13/02 9:31 p.m.



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