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The difference between speed and velocity

  1. Oct 6, 2004 #1
    Hi all,
    I think the title says it all :P..
    What is the difference between velocity and speed? I understand that velocity is a fair bit more complicated than speed. However, I often use the word "velocity" but meaning speed.

    At school, the teachers say "just assume that speed and velocity are the same" (to those few that actually know what speed is!! lol :rofl: ).

    So; what's the difference? :shy:

    Thanks in advance.. :)
  2. jcsd
  3. Oct 6, 2004 #2


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    Velocity has a DIRECTION as well as a MAGNITUDE (that is, velocity is a VECTOR quantity if you've learnt that term yet)
    The magnitude of velocity is called SPEED (just a POSITIVE number/scalar, not a vector)
  4. Oct 6, 2004 #3
    There is a little difference between two concepts: velocity and speed. First of all, let's regard that you are at axis-x, to 3 meters from origin of cartesians system, so you walk to origin. Later, you walk again more 4 meters at axis-y. So, your displacement is 5 meters, according Pitagoras' theorem, but, the distance that you've covered is 7 meters. In others terms, the displacement is a vector, then, depend only two points( at this case is final point minus initial point). The distance is what you really walked. Therefore the velocity is the time variation of displacement and the speed is the time variation of distance.
    Last edited: Oct 6, 2004
  5. Oct 6, 2004 #4


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    Every work day, I leave my home to drive to my work which is 20km West. When I am on the highway I set my cruise control to 100km/hr. That is my speed it is the same both on my way to work and on my way home. My velocity however is different in the morning then in the evening. In the morning my velocity is 100 km/h EAST, in the evening it is 100 km/h WEST. Thus it requires 2 numbers to specify velocity, it is possible to have a negative velocity. Speed on the other hand is a single positive number.

    Edit to avoid confusion, I work at night!
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