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Speed vs. Velocity question

  1. Oct 11, 2011 #1
    I understand the basics of speed and velocity, but I got a rather backhanded question on a recent test that I believe was marked incorrectly.

    Q: A baseball is thrown toward home plate. Is this a speed or a velocity?

    I said it was a speed, the ball could have been thrown from anywhere toward home plate. When I asked why it was a velocity, the response was that although the direction is unknown, it still has a direction. But then by that logic, all speeds would be velocities because they have to be traveling in a direction, even if it is not given. Did my teacher screw me over? Where am I going wrong?
     
  2. jcsd
  3. Oct 11, 2011 #2

    symbolipoint

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    Without being too picky, speed is a size. Velocity is that size combined with a direction.

    Look for the meanings of the words, "scalar", and "vector".
     
  4. Oct 11, 2011 #3

    Dale

    Staff: Mentor

    I would say it is neither. It is a direction. Speed is a magnitude, and velocity is a magnitude and a direction.

    Toward home plate is a valid direction. It means from the baseballs current location draw a line to home plate and the velocity is parallel to that line.
     
  5. Oct 11, 2011 #4

    cepheid

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    It's definitely a poorly-phrased question. "A baseball is thrown towards home plate. Is this a speed or a velocity?" Well, what does "this" refer to? Does it refer to the action of throwing a ball that was described in the previous sentence? If so, then "this" is neither a speed nor a velocity. It's a description of something that some person did. If you want to ask students to identify the type of a physical quantity, then you have to actually provide a physical quantity in your description. E.g. a ball is moving at 3.0 m/s towards home plate. Is this quantity mentioned above a speed or a velocity? Something like that would have been much better, in my opinion.
     
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