Increasing velocity graph

  • Thread starter Ryker
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  • #1
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Increasing velocity, when velocity is negative

Basically, I just wanted to make sure I got this right. If velocity is negative, but the speed is decreasing, the velocity is increasing, right? On the other hand, if velocity is negative and is getting even more negative, then velocity is decreasing. Am I getting this right or is it the other way around?
 
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  • #2
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First you need to be clear about velocity and speed.
Velocity has direction, and when you talk about positive and negative velocities, it usually just indicates the direction.
So, if a positive velocity is one to the right, then negative simply means the velocity is to the left, for example.
The positive and negative sign is not an indicator of whether or not the object is getting faster or slower, just which way it is moving.
The speed of the object is just "how fast" it's going. This is the numerical part of the velocity without the sign.
The measure of increase or decrease in a speed or velocity is acceleration.
To answer your question, when you say "velocity is negative" it simply indicates the direction of motion. (to the left, say). If the speed is decreasing, the object is getting slower. So, the object is moving to the left with a speed that is decreasing. Fine so far!
Put some example numbers to it...
t vel
1 -5
2 -4
3 -3
4 -2
This is velocity (m/s) over 4 seconds, showing the object getting slower in the direction to the left.
Yes, the numbers are increasing because they are getting less negative. So, technically, the velocity is increasing.
This is because the object is subject to an acceleration (+ive) in the direction to the right. Imagine it to be caused by friction, a force pointing to the right, against the motion to the left. A force to the right will produce an acceleration to the right.
 
  • #3
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Thanks, Stonebridge.
 

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