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Problem with the word (deceleration)

  1. Jan 9, 2013 #1
    Hi all, i think the word deceleration is used incorrectly and can cause problems for students learning physics
    For example, if i start from rest and run as fast as i can until i eventually more at a constant speed. Then my interperetation of this is that (i) i accelerate at some rate (ii) continually reduce my acceleration until, (iii) I move with an approximate constant speed.
    The word decelerate implies a relatively smaller magnitude acceleration ( as in (ii) above.
    Often, deceleration is used to describe a reverse acceleration without any consideration of its magnitude as in example 2.

    If I start from rest, run as fast as possible to top speed and stop as quick as possible. For this situation my so called deceleration has a higher magnituded than the forward acceleration.

    Am I on the right track or do I simply misunderstand the English language?
  2. jcsd
  3. Jan 9, 2013 #2


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    For the first case, no, "decelerate" does not imply slower acceleration. For the second....so what? I don't see what the problem is.
  4. Jan 9, 2013 #3
    Deceleration is in reference to an object slowing down. So, in your scenario, you would have acceleration while attempting to get to your "fastest" speed and deceleration as you attempt to stop.

    Notice that I did not say positive or negative there. This is all dependent on how one labels their coordinate system.
  5. Jan 9, 2013 #4


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    If you avoid using the word "decelerate" except when describing real cars in traffic situations then you will have no difficulty. Positive and negative acceleration are all you need and the Maths takes care of everything.

    'Moving backwards' and 'forwards' could also give problems but we usually discuss positive and negative velocities in Physics. AND in front or behind would usually be indicated by a simple (co-ordinate) sign.
  6. Jan 9, 2013 #5


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    No. Acceleration does not imply a smaller magnitude acceleration. Any time the velocity is still increasing that's an acceleration. For deceleration you need the velocity to reduce.

    Deceleration can have a very large magnitude. In fact I would argue that in every day life the magnitude of the deceleration you encounter is normally larger than acceleration.
  7. Jan 10, 2013 #6
    The word is "deceleration", not "deacceleration".
  8. Jan 16, 2013 #7
    Thanks for all comments. All points taken. However, I still have a problem with the English language.
    Yes deceleration is a reverse acceleration for example applying the brakes in a car. Yes you decelerate.
    But the word (de) _ hits me.:redface:
  9. Jan 17, 2013 #8


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    The problem is not so much the word "deceleration", which means "reduction of speed", but rather the word "acceleration", which has two different meanings:
    - vectorial : any change of the velocity vector
    - scalar : increase of velocity vector magnitude (speed)
    That ambiguity is causing much more confusion for students.
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