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Physical meaning of a Metre-Second? [or (Kg · s) or (N · s) ]

  1. May 17, 2013 #1
    We all understand what metres PER second (m/s) physically means... but,
    What I was wondering was what does a 'metre-second' actually mean? Or does it have a physical meaning at all!

    As an example:

    If we take the units for Dynamic viscosity we have:

    Kilogram per metre second ( Kg / m.s )

    On a side note, in relation to my above example:
    The SI physical unit of dynamic viscosity is the pascal-second (Pa·s), which is identical to
    Kg. m-1.s-1 = Kg / (m s)

    Another example, of a similar type, would be the standard unit of momentum, which is:
    Kilogram-metre per second (kg · m/s or kg · m · s-1 ) which in SI units is equal to Newton-second (N · s)

    In this example we have both a Kilogram-metre and, in SI, a Newton-second!
    I can easily conceptualise the idea of, say, 1 Metre every 1 Second (m/s) but Im finding it hard to conceptualise this concept!

    How exactly could one have, in the physical world, a metre-second (m · s), kilogram-metre (Kg · m) or Newton-second (N · s)?
  2. jcsd
  3. May 17, 2013 #2


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    If you could snort a white powdery substance from the surface of a mirrored conveyer belt moving at a fixed speed using a stationary rolled up piece of currency with a diameter measured in meters and had a certain number of seconds to do so, the "meter second" could be used as a relevant measure.
  4. May 17, 2013 #3


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    :rofl: :rofl:

    Never used metre-second but for something like the N*s, it would be the force acting over a period of time such that the Impulse = Force*time

    For something like kg-m, this could be something like a mass acting a distance. For example, if you have a shaft with an unbalance in it (center of rotation does not coincide to where the mass acts), you quantify the unbalance as a mass-eccentricity.

    Mass eccentricity me = mass*distance, usually given in gram-cm or some unit like that.
  5. May 17, 2013 #4
    would the force acting over a period of time not be Newtons per second ( N/s )?
    Last edited: May 17, 2013
  6. May 17, 2013 #5


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    That would give you the rate of change of force. A typical Force-time graph looks like this:


    The area under the graph gives the impulse which is the same as the change in momentum.
  7. May 18, 2013 #6
    Very good!
    I thought of a tunnel's price (tunnel lenght multiplied time of realization) but you beat me...
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