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

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Discussion Overview

The discussion revolves around the physical meaning of the unit 'metre-second' (m·s) and its relation to other units such as dynamic viscosity (kg/m·s), momentum (kg·m/s or N·s), and the implications of these units in physical contexts. Participants explore conceptual understandings and applications of these units in various scenarios.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants express difficulty in conceptualizing the physical meaning of 'metre-second' (m·s) compared to more intuitive units like metres per second (m/s).
  • Dynamic viscosity is discussed with reference to its units (kg/m·s) and its equivalence to pascal-seconds (Pa·s), prompting questions about the physical interpretation of these units.
  • One participant suggests that 'N·s' could represent force acting over time, relating it to impulse (Impulse = Force × time), though this interpretation is not universally accepted.
  • Another participant proposes that 'kg·m' could represent mass acting over a distance, using the example of mass eccentricity in a rotating shaft.
  • There is a challenge regarding the interpretation of force over time, with a participant questioning whether it should be expressed as Newtons per second (N/s) instead of N·s.
  • A humorous example involving a conveyor belt and a rolled-up piece of currency is presented to illustrate a potential application of the 'metre-second' unit.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the physical meaning of 'metre-second' or the interpretation of related units. Multiple competing views and interpretations remain present throughout the discussion.

Contextual Notes

Some discussions hinge on the definitions and contexts of the units, with unresolved assumptions about their applications and implications in physical scenarios.

CF.Gauss
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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 I am 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)?
 
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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.
 
jbriggs444 said:
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.

:smile: :smile:


CF.Gauss said:
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 I am 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)?

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.
 
rock.freak667 said:
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

would the force acting over a period of time not be Newtons per second ( N/s )?
 
Last edited:
CF.Gauss said:
would the force acting over a period of time not be Newtons per second ( N/s )?

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

09_03Figure.jpg



The area under the graph gives the impulse which is the same as the change in momentum.
 
jbriggs444 said:
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.
Very good!
I thought of a tunnel's price (tunnel length multiplied time of realization) but you beat me...
 

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