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  • Kg m/s N s and N

    What is the difference between Kg m/s and Newtons when talking about the average force? This is for a problem regarding momentum and impulse, etc.

  • #2
    Re: Kg m/s N s and N

    Newtons are a measure of force. An average force would also be measured in newtons. In contrast, momentum and impulse are measured in kgm/s.

    When a force is applied to an object for a period of time, the force delivers an impulse to the object. An impulse is a change in momentum:
    Force x Time = Impulse = Change in momentum
    (if you know integral calculus, the impulse is the integral of the force over time)
    Now, if you divide the impulse by the time during which the force was applied, you obtain the average force during that time:
    Avg force = Impulse Time
    Remember, the units of momentum and impulse are kgm/s. So, dividing an impulse by time gives you kgm/s2. But kgm/s2 is exactly how a newton is defined:
    1 newton = 1 kgm/s2
    And newtons are a measure of force. So, when you divide the impulse by time, you are calculating the (average) force.

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    • #3
      Re: Kg m/s N s and N

      Im just wondering I have data in N/s is this the same as kg.m/s or how do i change it to kg.m/s

      Thanks in advance

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      • #4
        Re: Kg m/s N s and N

        looks to me like you still need to find a distance something moved over that time to get power.

        Comment


        • #5
          Re: Kg m/s N s and N

          "Im just wondering I have data in N/s is this the same as kg.m/s or how do i change it to kg.m/s

          Thanks in advance "


          Answer: Doing problems like this requires unit analysis.

          Newton=mass(kg)*acceleration due to gravity(m/s^2)=kg*m/sec^2

          Time=sec

          The only way to relate time and force the way you request is to multiply the two
          N*Time=(kg*m/sec^2)*sec=kg*m/sec or N*s
          *the sec^2 in the denominator is canceled out to a single sec by the unit of time in the numerator of the multiplier

          the unit analysis for N/s is as follows:
          N=(kg*m/sec^2)*(1/sec)=kg*m/s^3

          Depending on the context of the problem you may or may not be able to use these units.
          For example, if you know that a force of 20 N was applied to hold a box in static equilibrium for one minute, then it is known that 1200 N*s or 1200 kg*m/sec is applied to the box. this is the only type of problem I can think of relating the two.

          hope this helps

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          • #6
            Re: Kg m/s N s and N

            It seems unlikely that you would have a measurement in N/s. That would be (as stated above) a unit of kg.m/s3, which seems strange.

            Is it possible that your unit is actually N.s? (That is, Newtons * seconds). That would in fact be equal to kg.m/s, which is what you wanted.

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            • #7
              Re: Kg m/s N s and N

              Originally posted by Unregistered View Post
              It seems unlikely that you would have a measurement in N/s. That would be (as stated above) a unit of kg.m/s3, which seems strange.

              Is it possible that your unit is actually N.s? (That is, Newtons * seconds). That would in fact be equal to kg.m/s, which is what you wanted.
              F*t, or the integral for a varying force, is impulse, equal to the change in momentum of the body acted upon. It is very common in rocket problems, but applicable to other things.

              However, the derivative of force with respect to time is also important, dF/dt = m*da/dt. The derivative of acceleration, da/dt, is known as jerk, and is closely related to "ride quality" in everything from cars to elevators (Amusement park rides may consider high jerk good).

              As both have uses, I think we need a better description of the data and its meaning or use from the poster who asked the question.

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              • #8
                Re: Kg m/s N s and N

                It is possible to have N/s units.

                Consider calculating the power required for a motor moving fluid. The fluid has a weight of so many N, is moving up a distance of so many m, and this is happening each s. So, the power required would be in (N/s)*m = W. But what is the name of this intermediate unit in kg m / s3? It seems to have no name.

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                • #9
                  Re: Kg m/s N s and N

                  THANK YOU SO Much


                  Originally posted by Roy Nakatsuka View Post
                  Newtons are a measure of force. An average force would also be measured in newtons. In contrast, momentum and impulse are measured in kgm/s.

                  When a force is applied to an object for a period of time, the force delivers an impulse to the object. An impulse is a change in momentum:
                  Force x Time = Impulse = Change in momentum
                  (if you know integral calculus, the impulse is the integral of the force over time)
                  Now, if you divide the impulse by the time during which the force was applied, you obtain the average force during that time:
                  Avg force = Impulse Time
                  Remember, the units of momentum and impulse are kgm/s. So, dividing an impulse by time gives you kgm/s2. But kgm/s2 is exactly how a newton is defined:
                  1 newton = 1 kgm/s2
                  And newtons are a measure of force. So, when you divide the impulse by time, you are calculating the (average) force.

                  Comment


                  • #10
                    Re: Kg m/s N s and N

                    helo guys am realy gr8ful you guys have just saved me

                    Comment


                    • #11
                      Converting gravity to Newtons

                      How do you convert the force of gravity (9.8m/s2) into Newtons?

                      Comment


                      • #12
                        Re: Converting gravity to Newtons

                        Originally posted by Unregistered View Post
                        How do you convert the force of gravity (9.8m/s2) into Newtons?
                        9.8 m/s is actually the acceleration of freefall. The force is that acceleration times the mass (F = m*a). 1 kg acted on by standard gravity will fall unless a counterbalancing force of 9.8 N is exerted on it.

                        The "official" value for standard gravity is 9.80665 m/s (or N/kg). However local gravity varies about 0.5% from equator to pole at sea level and also varies with altitude. It is common to just assume standard gravity to estimate the forces and rely on the safety margin of a structure. However, if the force is needed to high accuracy, you must determine local gravity. There are formulas that consider latitude and height above sea level.

                        Comment


                        • #13
                          Re: Kg m/s N s and N

                          I have this problem:

                          While two forces act on it, a particle is to move at the constant velocity = (2.85 m/s) - (-3.88 m/s). One of the forces is 1 = (2.45 N) + (-5.35 N). What is the other force?
                          how do I convert m/s to N?

                          Comment


                          • #14
                            Re: Kg m/s N s and N

                            Question: F = m * a
                            a = denoted as m/sec2
                            how does this relate to N/kg?

                            Comment


                            • #15
                              Re: Kg m/s N s and N

                              Originally posted by Unregistered View Post
                              Question: F = m * a
                              a = denoted as m/sec2
                              how does this relate to N/kg?
                              The newton is a derived unit and has dimensions of a kgm/s, defined by F = ma.

                              In the expression N/kg, if you replace newton with kgm/s, the kg cancel out, leaving acceleration, m/s.

                              Comment

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