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Only vectors can be negative?

  1. Dec 21, 2011 #1
    I want to make the above claim in a physics paper for my intro to physics class, but first I want to confirm if it is absolutely correct. My reasoning goes that Force, acceleration, and velocity, can be negative, but mass and kinetic energy cannot be. Is my conjecture sound?
     
  2. jcsd
  3. Dec 21, 2011 #2
    no. as one example, check on the negative potential of a gravitational field...potential energy being a scalar.

    Another example would be electrical potential,,,,positive and negative.

    How about time?
     
  4. Dec 21, 2011 #3
    I think mass is defined to be positive. It follows that kinetic energy is positive since it involves mass (m ≥ 0) and the squared modulus of velocity, which is necessarily positive (or zero).

    I would be hesitant about answering your question with a yes though. The distinction you are looking for (I think) is that vector quantities have what we interpret as direction, while scalar quantities don't. In your examples force, acceleration and velocity are all vector quantities, while mass and kinetic energy are scalar quantities.

    And as Naty1 says, potential energy can be negative.
     
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