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Diffrence between negative accelaration and positive decelaration?

  1. May 9, 2010 #1
    Hi,
    I have the following question.
    What is:
    A. Positive accelaration.
    B. Negative accelaration.
    C. Positive decelaration.
    D. Negative decelaration.

    If im not wrong then:
    A is just getting faster.
    B is getting slower(Not sure about that)
    C is just getting slower.
    D is going backwards??? Thats the one I really dont understand.

    Thank you for the help.
     
  2. jcsd
  3. May 9, 2010 #2

    diazona

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    Homework Helper

    We don't really talk about "deceleration" in physics, at least not as a technical term. So I'm not quite sure what to say about C and D.

    For A and B, if "acceleration" is being used with its normal physics definition, all "positive acceleration" means is that the velocity is becoming more positive with time. As for what that means physically, it depends on which way the object is moving. For instance, think about this: if an object with positive velocity has positive acceleration, is it speeding up or slowing down? If an object with negative velocity has positive acceleration, is it speeding up or slowing down?
     
  4. May 9, 2010 #3
    Right so a object with positive velocity has positive acceleration it would be...it would be speeding up.
    A object with negative velocity has positvie acc then it would still be speeding up right?
    But wait negative velocity is what?

    But thanks for the answer!!
     
  5. May 9, 2010 #4

    diazona

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    Negative velocity is velocity in the negative direction.

    If you're not used to thinking about velocity as having a sign, think of it like a number line. Positive is to the right, negative is to the left. An object with positive velocity is moving to the right, and an object with negative velocity is moving to the left. Now, to rephrase my question from before: if an object with negative velocity (moving to the left) has a positive acceleration (that means its velocity is getting more positive, i.e. more toward the right), is it speeding up or slowing down?
     
  6. May 10, 2010 #5
    Its slowing down?
    Well if I understood you right then as it has a negative velocity moving to the left then it would mean that if it had a positive acceleration wait no. Then its speeding up.
    Ohh god im confused.
     
  7. May 10, 2010 #6
    If you visualize it as a number line as the other poster suggested, you could say that the object in motion acclerates to the right (positive acceleration), accelerates to the left (negative acceleration), accelerates to the left (positive deceleration) and accelerates to the right (negative deceleration.) No, deceleration is not a physics term, but I'm assuming they are using it as a layman would, the opposite of the generally accepted definition of "accleration." So negative deceleration is a double negative therefore equal to acceleration.
     
  8. May 10, 2010 #7
    Wow cool thanks I understood that good.
    Thank you to all to make the effort to explain!!!
    Thank you!!
     
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