Conservation of momentum and energy

[studiot]

 

 

Motion at constant velocity involves no net force.

 

 

I beg to differ, this statement is ambiguous at best and can be misleading.

I have personal experience of disasters that occur when engineers fail to appreciate the need for proper thrust blocks in pipelines.

 

Please can we just collectively establish what capiert is trying to present and move forward?

Edited July 6, 2016 by studiot

[Capiert]

I beg to differ, this statement is ambiguous at best and can be misleading.

I have personal experience of disasters that occur when engineers fail to appreciate the need for proper thrust blocks in pipelines.

 

Please can we just collectively establish what capiert is trying to present and move forward?

Yes, it looks like we are coming a bit forward.

Please expain (a few sentences) what happens to the pipelines (with & without) thrust blockers.

It sounds like big problems, against naive science.

 

E.g.

If momentum

mom=m*v

the engineering toolbox uses speed "squared",

instead of only speed for the (momentum's) force calculation.

(That tends to an energy calculation, without the half in KE, for me.)

Perhaps insurance, against worst case?

 

http://www.engineeringtoolbox.com/forces-pipe-bends-d_968.html

 

I'd also expect a straight, long pipe would get pushed, or dragged,

by the viscous friction (force), in the direction of the flow speed.

Versus no flow.

Edited July 6, 2016 by Capiert

[studiot]

Yes, it looks like we are coming a bit forward.

Please expain (a few sentences) what happens to the pipelines (with & without) thrust blockers.

It sounds like big problems, against naive science.

 

E.g.

If momentum

mom=m*v

the engineering toolbox uses speed "squared",

instead of only speed for the (momentum's) force calculation.

(That tends to an energy calculation, without the half in KE, for me.)

Perhaps insurance, against worst case?

 

http://www.engineeringtoolbox.com/forces-pipe-bends-d_968.html

 

It would be generous and helpful if we could all dispense with comments like the underlined henceforth.

 

In brief answer to the rest of your post:

 

When a fluid, travelling at constant fluid velocity, passes round a bend or elbow in a pipe, the pipe exerts force on the fluid to turn it around the bend.

In turn the fluid exerts a reaction force on the pipeline.

 

This force can be considerable, enough to blow the joints or burst the line (as I have seen).

Or the line may simply be displaced.

It is this force that causes a hosepipe to snake about.

This force is there even without friction.

If we add friction into the theory the fluid will exert a bursting force on every flange and coupling joint, even in a straight pipline.

 

Does this help

Edited July 6, 2016 by studiot

[swansont]

In brief answer to the rest of your post:

 

When a fluid, travelling at constant fluid velocity, passes round a bend or elbow in a pipe, the pipe exerts force on the fluid to turn it around the bend.

In turn the fluid exerts a reaction force on the pipeline.

I am compelled to point out that turning a bend is not a case of constant velocity: there is a change in direction, and as velocity is a vector, this involves an acceleration. Thus a force must be exerted to make the fluid (or object) change direction. The momentum of the fluid (or object) changes.

[Capiert]

Does this help

Yes. Fascinating.

What about the calculations? v vs v^2.

There is a cliff, a gap, of understanding.

I see (fluid's) momentum in 1 direction, e.g. x

being converted (e.g. destroyed (=decelleration) in 1 direction & newly recreated (=acceleration, of the fluid particles))*

into e.g. the y direction.

(* I know physicists, don't like to hear that (destroyed/created)

but that's how I think about it easiest.)

 

But I suspect, more complicated behaviour is happening,

e.g. like (electron) back splashing recoil, in (old radio) vaccum tubes,

as analogy.

 

Maybe you could continue (explaining) a bit more?

I am compelled to point out that turning a bend is not a case of constant velocity: there is a change in direction, and as velocity is a vector, this involves an acceleration. Thus a force must be exerted to make the fluid (or object) change direction. The momentum of the fluid (or object) changes.

Sounds good. Edited July 6, 2016 by Capiert

[studiot]

I thought swansont might say that, but in fluids there are two methods of analysis, relative to the flow and relative to a fixed reference.

 

The velocity is constant, relative to the flowlines.

 

But this is a boring non productive argument.

 

 

capiert this might help if you can follow it.

 

http://www.efm.leeds.ac.uk/CIVE/FluidsLevel1/Unit03/T5.html

[Capiert]

I thought swansont might say that, but in fluids there are two methods of analysis, relative to the flow and relative to a fixed reference.

I also had a feeling Swansont would top us,

with acceleration.

I was disappointed before,

but it helped me fit my recreation concept,

so I was relatively content, after.

Milikan's oil drop experiment popped in my head:

constant speed under gravity (acceleration),

(because of viscous friction force compensation,

but the drops travel at steady speed.)

Naturally, why?

(do we come to a steady speed, equilibrium,

even parachuters do that when sky diving.)

 

 

The velocity is constant, relative to the flowlines.

I'll still need a formal education there.

(That's too close=near to reality (vocabulary, monotiny), for me.

It's as bad as "tasty" for food. It tells me too little, on it's own. Tendencial. (Tendancy, positive feedback.)

 

But this is a boring non productive argument.

That's probably why, once I know & recognize it.

Til then.

 

 

Capiert this might help if you can follow it.

 

http://www.efm.leeds.ac.uk/CIVE/FluidsLevel1/Unit03/T5.html

The tricky part for me is the mass flow calc,

across (=thru) an area.

(It's a little too abstract, =virtual, for me, yet.)

I'm still not happy with it,

considering

I've tried to do similar

with electricity,

for the amount of electron mass (travelling thru an area)

per ampere.

I think it was something like 9 ng/s.

 

I need some time to work on it.

But glad you continued.

 

The other thing that occured to me,

is a steady speed,

water is still moving;

but there is a force (pressure) pushing it

(thru the hose or pipe)

so it stays moving.

 

(It all boils back down to

force produces constant speed,

instead of acceleration, paradox, mystery.

E.g. Swansont's: "Motion at constant velocity involves no net force.")

 

 

& curved wire, looped turns,

must also have,

electron direction change,

perhaps causing the electromagnetic (radiation, magnetism)

that it does.

E.g. The curl

around the wire,

based on momentum.

 

Those are the things

I have to think about, further.

 

But the most interesting example

you mentioned today,

was the dancing garden hose.

I suspect there is a lot more to it.

That caught my attention.

Edited July 6, 2016 by Capiert

[swansont]

I also had a feeling Swansont would top us,

with acceleration.

I was disappointed before,

but it helped me fit my recreation concept,

so I was relatively content, after.

Milikan's oil drop experiment popped in my head:

constant speed under gravity (acceleration),

(because of viscous friction force compensation,

but the drops travel at steady speed.)

Naturally, why?

(do we come to a steady speed, equilibrium,

even parachuters do that when sky diving.)

There's a drag force which is in the opposite direction of the motion. As it's velocity dependent, you will reach a condition of zero net force at some speed. No net force means no acceleration, so the velocity will be constant.