Re Calculating Newtons in Joules and Jouless by TaylorRandle

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									                           Re: Calculating Newtons in Joules and Joules/s

Re: Calculating Newtons in Joules and Joules/s

Source: http://sci.tech−archive.net/Archive/sci.physics/2006−07/msg00705.html



      • From: "Dennis B" <Utopian@xxxxxxxx>
      • Date: 6 Jul 2006 22:50:12 −0700



Dennis B wrote:

       Randy Poe wrote:

               Dennis B wrote:

                       PD wrote:

                               Dennis B wrote:

                                      Randy Poe wrote:

                                              Dennis B
                                              wrote:

                                                      You
                                                      are
                                                      blind
                                                      if
                                                      you
                                                      cannot
                                                      see
                                                      that
                                                      force
                                                      is
                                                      energy.


                                              Saying it
                                              over and
                                              over won't
                                              make it so.


                                                      Force
                                                      can
                                                      be


Re: Calculating Newtons in Joules and Joules/s                                  1
                         Re: Calculating Newtons in Joules and Joules/s
                                                   measured
                                                   in
                                                   J/m.


                                           Yes, and
                                           energy
                                           can't.


                                                   The
                                                   distinctions
                                                   between
                                                   momentum,
                                                   energy,
                                                   work,
                                                   and
                                                   force
                                                   are
                                                   that
                                                   they
                                                   are
                                                   different
                                                   measurements
                                                   of
                                                   one
                                                   thing:
                                                   Energy.


                                           Incorrect.


                                                   For
                                                   everything
                                                   is
                                                   energy.
                                                   You
                                                   cannot
                                                   argue
                                                   with
                                                   that.


                                           Yes I can.

                                           − Randy


                                   I don't have the time or
                                   energy at the present

Re: Calculating Newtons in Joules and Joules/s                            2
                         Re: Calculating Newtons in Joules and Joules/s
                                   moment to respond to all
                                   of the messages in detail.
                                   Not that I don't intend to. In
                                   the interim,
                                   perhaps following evidence
                                   will prove to you that
                                   momentum, force,
                                   work, and energy are all
                                   unified:

                                   Momentum = mv
                                   Force = (delta)mv
                                   (Kinetic) Energy = 1/2mv^2
                                   work = 1/2mv^2

                                   In other words, momenum,
                                   force, kinetic energy, and
                                   work are all
                                   measurements of mv...

                                   Perhaps now you will begin
                                   to understand my
                                   perspective?


                            A couple of comments:

                            These formulas you have here are NOT
                            universal definitions, despite
                            what you may have read. They work
                            sometimes, under some circumstances,
                            for some kinds of things.

                            Just because m and v appear in all of them
                            does NOT mean that they are
                            the same thing. For example, if momentum
                            and energy were the same
                            thing, then if the momentum for an object A
                            happened to be the same as
                            the momentum for object B, then you would
                            expect the energies to be the
                            same, too. But they're not. Let's take an
                            example:
                            Object A: m = 2 kg, v = 4 m/s
                            Object B: m = 4 kg, v = 2 m/s
                            Here momentum of A = (2 kg)(4 m/s) = 8
                            kg*m/s
                            And momentum of B = (4 kg)(2 m/s) = 8
                            kg*m/s. They have the same
                            momentum. So if momentum and energy are
                            the same thing, then if these

Re: Calculating Newtons in Joules and Joules/s                            3
                           Re: Calculating Newtons in Joules and Joules/s
                              two momenta for A and B are equal, then so
                              should be the energies.
                              Here energy of A = 1/2(2 kg)(4 m/s)^2 = 16
                              J
                              But energy of B = 1/2(4 kg)(2 m/s)^2 = 8 J.
                              Not the same.
                              So the momenta of A and B are equal, but
                              the energies of A and B are
                              NOT equal.



                                        −Dennis


                      I have a question for you: If the 2kg and 4kg masses have the
                      same
                      momentum, what would happen if they each collided with a
                      3 kg mass
                      (each having identical properties) and transferred their
                      momentum?


              In collisions, typically one mass doesn't "transfer it's momentum"
              to another. Most of the time both masses end up with some
              momentum and KE after the collision.

              The amount of momentum and KE transferred will be
              different for the 2 kg and 4 kg masses if you assume
              perfectly elastic or perfectly inelastic collisions.


                      Since the 2kg mass and the 4kg mass have the same
                      momentum, wouldn't
                      both of the 3 kg masses have the same momentum as well?


              Momentum and energy are separately conserved. Due to
              those requirements, your hypothetical momentum transfers
              can't both happen.

              If the 3 kg mass were to get all of the momentum of the
              2 kg mass, it would be moving at 2/3 of the velocity and
              would therefore have (3/2)*(4/9) = 2/3 of the KE that the
              2 kg mass originally had. That is possible in the right
              inelastic collision, with the remaining 1/3 being lost to
              heat.


       What does the (4/9) represent?


Re: Calculating Newtons in Joules and Joules/s                                        4
                             Re: Calculating Newtons in Joules and Joules/s


                If the 3 kg mass were to get all of the momentum of the
                4 kg mass, it would be moving at 4/3 of the velocity and
                would have (3/4)*(16/9) = 4/3 of the KE that the 4 kg mass
                originally had. That is impossible.


        What does the (16/9) represent?



                It is not possible for a 4 kg mass to transfer all of its momentum
                to a 3 kg mass in a collision.

                − Randy


        Make it two 4 kilogram masses instead of two 3 kg masses. And make the
        collision totally inelastic, so that all of the momentum is
        transferred. Then what would the results of a transfer of momentum be?
        I don't see why the velocities would be any different. Although the 2kg
        and 4kg masses differ, the 2kg mass travels at a greater velocity to
        make up for the difference so that the momentum of the two is the same.
        Therefore, I would expect that the 2kg mass should have just as much of
        an impact as the 4 kg mass.

        −Dennis


Perhaps I should ask what the results of a perfectly elastic collision
would be as opposed to an inelastic collision. The reason being that
while studying momentum I was astonished to find that in an inelastic
collision, the colliding masses supposedly stick together, presumably
such that both then travel together. Yet, I ask...is it not possible
for the mass at rest to absorb all of the energy of the colliding mass
and accelerate to the same velocity of the colliding mass which, having
given up all of it's kinetic energy, then effectively absorbs the zero
velocity "momentum" of the mass at rest such that it stays put while
the other mass carries on where the other left off. That would be a
true transfer of momentum. An inelastic collision wherein both masses
continue onward together after the collision does NOT represent a
complete transfer of momentum in my opinion, since the colliding mass
retains some of it's momentum.

−Dennis

.




Re: Calculating Newtons in Joules and Joules/s                                       5

								
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