Steve,
Lets make this more complicated. Where do tensors fit in?
If there is a pressure surge in a pipeline how does one translate that into a force that makes the pipeline shake, rattle and roll. Any good engineering texts and books on the subject?
The momentum of the fluid if change as the velocity is changed.
Geoff
Steve McKenzie <Mechproj@xtra.co.nz> wrote:
One last try with reference to your last sentence. Consider a mass whirling at the end of a string, horiz plane. The kinetic energy is 1/2mV^2, as you say. Because momentum is a vector quantity is is dealt with by resolving into a reference frame. In cartesians x axis , at say 6 oclock the momentum is mV and at 9 oclock it is 0. So the momentum in the x direction has changed as the mass has moved through 90 degrees but the energy has stayed the same. As I said mixing vector quantities with scalars is not a good thing to do. If you wish to redefine momentum as the product of speed and mass, then fine; the ballistics guys do it all the time.
But it aint physics.
Cheers
Steve
-----Original Message-----
From: <a href="/group/PipingDesign/post?postID=l4Q6AxD_sNUGyAYdhquFEHNNts1ekgxqQ8GzbdggdRftukYIUnlRfB7GuNLow-tHh3Tb84QRmuXUECpGHdP9RYNHsAvG">PipingDesign@yahoogroups.com</a> [mailto:<a href="/group/PipingDesign/post?postID=l4Q6AxD_sNUGyAYdhquFEHNNts1ekgxqQ8GzbdggdRftukYIUnlRfB7GuNLow-tHh3Tb84QRmuXUECpGHdP9RYNHsAvG">PipingDesign@yahoogroups.com</a>]
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Subject: Re: [PipingDesign] List Reborn
On Oct 19, 2005, at 10:14 PM, <Mechproj@xtra.co.nz> wrote:
> your comments treat speed the same as velocity. Velocity has a
> magnitude and a direction. If you change the direction, you change the
> velocity, but not necessarily the speed.
Presumably you're referring to speed as the magnitude of the velocity
vector. The relationship and the underlying physics still holds. The
change in momentum doesn't equal the change in energy, as we agreed,
because momentum can't equal energy. But the change in speed (or mass)
which causes a change in momentum also causes the kinetic energy to
change. That's because kinetic energy equals half the momentum times
the speed. If you change the momentum the kinetic energy inescapably
changes.
Christopher Wright P.E. |"They couldn't hit an elephant at
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[Non-text portions of this message have been removed] Received on Thu Oct 20 04:16:00 2005
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