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Homework Help: 8th Grader in Need of Help! I know barely any Physics!

  1. Sep 28, 2010 #1
    I know barely anything about Physics and this is the 1st Physics Class I've been in.

    1. The problem statement, all variables and given/known data

    Why can only a constant speed accelerate and not a constant velocity?



    2. Relevant equations

    None


    3. The attempt at a solution

    No idea....

    Please help!
     
  2. jcsd
  3. Sep 28, 2010 #2
    Since speed it a scalar quantity it only refers to how fast an object is moving. Velocity is a vector, meaning that its speed AND direction are important. Acceleration is also a vector quantity, so if an object's movement either changes direction, or goes faster, there is aceleration.

    If an object is moving at constant speed, it could change directions which is a form of acceleration, but it would still be going at the same speed.

    However, if an object is to be moving with constant velocity, it's speed and direction cannot change for it to be constant. It cannot accelerate
     
  4. Sep 28, 2010 #3
    Oh, that makes sense! Thanks! So Vector means that speed and direction are important? What is a "scalar quantity?" Thanks though :)
     
  5. Sep 28, 2010 #4
    scalar means only the magnitude, or size is important.

    So in the case of speed and velocity, the 'magnitudes' of their motion is how fast they are going
     
  6. Sep 28, 2010 #5
    I'm still not understanding... sorry, but what do you mean their size and magnitudes? What does size have to do with speed?
     
  7. Sep 28, 2010 #6
    I looked up the word scalar, so it's almost the opposite of Vector, it's when a quantity only relies on speed and not direction?
     
  8. Sep 28, 2010 #7
    a scalar does not have a direction, it is just some quantity, for example temperature is a scalar since it does not have a direction. Speed is also a scalar
     
  9. Sep 28, 2010 #8
    Okay, I think I understand! Thanks a lot! Hopefully I'll get better in Physics!
     
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