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Train Physics Problem

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  Train Physics Problem Fabian Russell <root@localhost.localdomain> - 2015-11-03 02:05 +0000
    Re: Train Physics Problem Fabian Russell <root@localhost.localdomain> - 2015-11-03 02:31 +0000
      Re: Train Physics Problem Fabian Russell <root@localhost.localdomain> - 2015-11-03 02:38 +0000
      Re: Train Physics Problem gillyshin <spectrum8@sincity.info> - 2015-11-03 04:38 +0000
        Re: Train Physics Problem gilber34 <fafa@invalid.com> - 2015-11-02 22:58 -0600
          Re: Train Physics Problem Fabian Russell <root@localhost.localdomain> - 2015-11-03 05:22 +0000
    Re: Train Physics Problem Odd Bodkin <bodkinodd@gmail.com> - 2015-11-03 08:38 -0600
      Re: Train Physics Problem Fabian Russell <root@localhost.localdomain> - 2015-11-03 18:19 +0000
        Re: Train Physics Problem Odd Bodkin <bodkinodd@gmail.com> - 2015-11-03 15:00 -0600
          Re: Train Physics Problem Fabian Russell <root@localhost.localdomain> - 2015-11-03 21:22 +0000
            Re: Train Physics Problem Odd Bodkin <bodkinodd@gmail.com> - 2015-11-03 16:55 -0600
              Re: Train Physics Problem Fabian Russell <root@localhost.localdomain> - 2015-11-03 23:19 +0000
          Re: Train Physics Problem Fabian Russell <root@localhost.localdomain> - 2015-11-03 21:31 +0000
            Re: Train Physics Problem Odd Bodkin <bodkinodd@gmail.com> - 2015-11-03 17:17 -0600
      Re: Train Physics Problem benj <none@gmail.com> - 2015-11-03 13:41 -0500
        Re: Train Physics Problem Fabian Russell <root@localhost.localdomain> - 2015-11-03 18:53 +0000
          Re: Train Physics Problem benj <none@gmail.com> - 2015-11-04 18:08 -0500
            Re: Train Physics Problem Fabian Russell <root@localhost.localdomain> - 2015-11-04 23:33 +0000
        Re: Train Physics Problem Odd Bodkin <bodkinodd@gmail.com> - 2015-11-03 15:10 -0600
          Re: Train Physics Problem Fabian Russell <root@localhost.localdomain> - 2015-11-03 21:48 +0000
            Re: Train Physics Problem benj <nobody@gmail.com> - 2015-11-04 02:45 -0500
    Re: Train Physics Problem "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-03 09:19 -0800
      Re: Train Physics Problem "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-04 15:15 -0800

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#530066 — Train Physics Problem

Attention physics enthusiasts:

In all of the information that I have encountered about train
physics -- and there is not a lot of material available -- the
energy required to move a train is calculated by considering
factors such a inertia (train mass), mechanical resistance (friction),
and air resistance (drag).

However, one significant factor is always ignored, and that is
the rotational energy of the wheel sets.

Why?  What is the reason for omitting the rotational energy?

In the US, a train wheel is very nearly 1 meter in diameter and
has a mass of 1000 kg.  The rotational energy for one wheel is
then 1/2 * I * w^2.  At 60 mph (27 m/s) speed, the energy is 179862 Joules.

At 4 wheel sets per car (8 wheels) with an average train containing
100 cars, the total rotational energy of the wheels is a whopping
143889600 Joules = 144 megajoules.

Yet this energy is ignored.

For a reference, see page 2 of this link:

http://s000.tinyupload.com/?file_id=07666111176590991515

This is a Microsoft Word (doc) file.

A LibreOffice (odt) version is here:

http://s000.tinyupload.com/?file_id=00684379287173743496

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#530067

On Tue, 03 Nov 2015 02:05:46 +0000, Fabian Russell wrote:

>
> the total rotational energy of the wheels is a whopping
> 143889600 Joules = 144 megajoules.
> 

I made an error converting linear to angular velocity.

The correct total should be 12340205 J = 12.3 megajoules,
which is still a whopping figure.

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#530068

On Tue, 03 Nov 2015 02:31:43 +0000, Fabian Russell wrote:

> 
> The correct total should be 12340205 J = 12.3 megajoules,
> which is still a whopping figure.
>

I incorrectly used 3.414159 as the value for pi.  It should
be 3.14159.  Apparently, I was thinking of the square root of 2.

Now, the correct figure is 14772639 J = 14.8 megajoules.

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#530077

On Tue, 03 Nov 2015 02:31:43 +0000, Fabian Russell wrote:

> 
> I made an error converting linear to angular velocity.
> 

No you didn't.  You were right the first time.  It's 144 Megajoules.

GI

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#530079

On 11/2/2015 10:38 PM, gillyshin wrote:
> On Tue, 03 Nov 2015 02:31:43 +0000, Fabian Russell wrote:
>
>>
>> I made an error converting linear to angular velocity.
>>
>
> No you didn't.  You were right the first time.  It's 144 Megajoules.
>
> GI
>

makes you think, what would a redesigned steam train look like now ?

using carbon fiber, remove most of the heavy stuff.....

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#530082

On Mon, 02 Nov 2015 22:58:04 -0600, gilber34 wrote:

> 
> makes you think, what would a redesigned steam train look like now ?
> 
> using carbon fiber, remove most of the heavy stuff.....
>

It would never work.  Locomotives have to be HEAVY.

In order to generate tractive effort, which is a different name for
the friction force, the locomotive wheels have to exert a tremendous
normal force (i.e. weight) on the rail.  Otherwise, the wheels will
slip and the train won't move.

Recall that the force of static friction = coefficient * normal force

F_static = u * N

For steel wheels on steel rail, the coefficient, u, is 0.3 - 0.4.

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#530117

On 11/2/2015 8:05 PM, Fabian Russell wrote:
> Attention physics enthusiasts:
>
> In all of the information that I have encountered about train
> physics -- and there is not a lot of material available -- the
> energy required to move a train is calculated by considering
> factors such a inertia (train mass), mechanical resistance (friction),
> and air resistance (drag).
>
> However, one significant factor is always ignored, and that is
> the rotational energy of the wheel sets.
>
> Why?  What is the reason for omitting the rotational energy?
>
> In the US, a train wheel is very nearly 1 meter in diameter and
> has a mass of 1000 kg.  The rotational energy for one wheel is
> then 1/2 * I * w^2.  At 60 mph (27 m/s) speed, the energy is 179862 Joules.
>
> At 4 wheel sets per car (8 wheels) with an average train containing
> 100 cars, the total rotational energy of the wheels is a whopping
> 143889600 Joules = 144 megajoules.
>
> Yet this energy is ignored.

I don't know that it's ignored, but let's put those large numbers in 
perspective.

Let's compare the rotational kinetic energy of the wheels to the 
translational kinetic energy of the wheels.
w = v/r, and for a disk wheel, I = (1/2)m*r^2.
So the rotational KE = (1/2)(1/2)m*r^2 * (v/r)^2 = (1/4)mv^2. The 
rotational KE of the wheels is thus half the translational KE of the wheels.

Now we can compare the translational kinetic energy of the wheels to the 
translational kinetic energy of the train as a whole.

As you say, 800 wheels on a 100-car train has a mass of about 800 metric 
tons. But the mass of a fully loaded train is about 10,000 metric tons. 
So the translational kinetic energy of the wheels is about 8% of the 
train's translational kinetic energy, and the rotational kinetic energy 
of the wheels is then about 4% of the train's total kinetic energy.

Not insignificant, but not huge either.

>
> For a reference, see page 2 of this link:
>
> http://s000.tinyupload.com/?file_id=07666111176590991515
>
> This is a Microsoft Word (doc) file.
>
> A LibreOffice (odt) version is here:
>
> http://s000.tinyupload.com/?file_id=00684379287173743496
>


-- 
Odd Bodkin --- maker of fine toys, tools, tables

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#530160

On Tue, 03 Nov 2015 08:38:49 -0600, Odd Bodkin wrote:

> 
> Not insignificant, but not huge either.
> 

Yes, that is correct.

This factor becomes even less significant in the everyday operating
conditions of track gradients where the gravitational forces on
a heavy train dwarf everything else.  A slight 2% grade can bring many
trains to a complete halt.

Trains also must dissipate all that huge energy as heat whenever they
slow to a stop.  Most locomotives can use "regenerative" braking where
the traction motors are run in reverse, using the magnetic field to
produce current.  The current is then directed to resistive elements to
produce waste heat.  Although it could be desirable, I doubt that it
would be possible to use batteries to store that energy, much like
in some automobiles.  AFAIK, no battery could absorb so much power
so quickly.

I wonder why no one else jumped on this question?  It is, after all,
pure physics.  Most would rather rabidly bark at global warming issues
which are not at all appropriate to this group.

But trains are the most efficient way to move stuff on land.  They
can beat trucks on all counts (except for expeditious point-to-point
delivery).  Any society that does not embrace trains is a losing society,
yet currently railroad trackage is being abandoned at a rapid rate.
Before too long, the US will possess only a few "backbone" rail corridors
with all other transport being inefficient and extravagant trucks and planes.

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#530200

On 11/3/2015 12:19 PM, Fabian Russell wrote:
> On Tue, 03 Nov 2015 08:38:49 -0600, Odd Bodkin wrote:
>
>>
>> Not insignificant, but not huge either.
>>
>
> Yes, that is correct.
>
> This factor becomes even less significant in the everyday operating
> conditions of track gradients where the gravitational forces on
> a heavy train dwarf everything else.  A slight 2% grade can bring many
> trains to a complete halt.
>
> Trains also must dissipate all that huge energy as heat whenever they
> slow to a stop.  Most locomotives can use "regenerative" braking where
> the traction motors are run in reverse, using the magnetic field to
> produce current.  The current is then directed to resistive elements to
> produce waste heat.  Although it could be desirable, I doubt that it
> would be possible to use batteries to store that energy, much like
> in some automobiles.  AFAIK, no battery could absorb so much power
> so quickly.
>
> I wonder why no one else jumped on this question?  It is, after all,
> pure physics.  Most would rather rabidly bark at global warming issues
> which are not at all appropriate to this group.

I suspect that no one jumped on it because it's an elementary 
calculation from freshman physics. It's not like it's unexplored 
territory, unknown to engineers and physicists alike.

I think one pervasive problem on this newsgroup is that lots of people 
think that their posts are interesting and should draw lots of 
attention. It's the attention that's really craved, not that the problem 
is really all that interesting.

>
> But trains are the most efficient way to move stuff on land.  They
> can beat trucks on all counts (except for expeditious point-to-point
> delivery).  Any society that does not embrace trains is a losing society,
> yet currently railroad trackage is being abandoned at a rapid rate.
> Before too long, the US will possess only a few "backbone" rail corridors
> with all other transport being inefficient and extravagant trucks and planes.
>

Mile-for-mile you are correct.
But trains are less efficient than a container ship, which beats it for 
efficiency mile-for-mile by a factor of 20 or so.
So trains are fine for same-continent commerce, ships are vastly better 
for intercontinental trade.

Large-scale shipping requires both warehousing and large depots, which 
are expensive. They also cause a mismatch between stored supply and 
actual demand. Modern commerce is much more geared to just-in-time 
supply, which then favors point-to-point delivery when same-continent. 
This is why trucking is favored over rail. On the other hand, the sharp 
rise in international trade over the last few decades has bumped up 
intercontinental shipping, for which rail is useless.


-- 
Odd Bodkin --- maker of fine toys, tools, tables

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#530213

On Tue, 03 Nov 2015 15:00:01 -0600, Odd Bodkin wrote:

> 
> I think one pervasive problem on this newsgroup is that lots of people 
> think that their posts are interesting and should draw lots of 
> attention. It's the attention that's really craved, not that the problem 
> is really all that interesting.
> 

Who cares about the reason, Oddball.  We all have our reasons, perverted
or otherwise.  To a genuine physicist, all problems, irrespective of the
source, should be an interesting challenge.  Else you are just a phony.

But *you* certainly seem intent on showing off your supposed powers of
psychological inference.

(Need I remind you that psychology is a pussy profession.)

> 
> Mile-for-mile you are correct.
> But trains are less efficient than a container ship,
>

I specified "land," which excludes ships.

But another question, energy for energy, would be more efficient
to offload a container ship in LA, transfer to rail, and then
transport to NYC.  Or would it be better to sail the same ship
from LA to NYC through the Strait of Magellan.  (This ship is
much bigger than Panamax.)

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#530248

On 11/3/2015 3:22 PM, Fabian Russell wrote:
> On Tue, 03 Nov 2015 15:00:01 -0600, Odd Bodkin wrote:
>
>>
>> I think one pervasive problem on this newsgroup is that lots of people
>> think that their posts are interesting and should draw lots of
>> attention. It's the attention that's really craved, not that the problem
>> is really all that interesting.
>>
>
> Who cares about the reason, Oddball.  We all have our reasons, perverted
> or otherwise.  To a genuine physicist, all problems, irrespective of the
> source, should be an interesting challenge.  Else you are just a phony.

Oh, but that's just not true, Fabian. Old, solved, and pedestrian 
applications just aren't the kind of thing that get physicists 
interested, unless they're specifically teaching beginning students.

>
> But *you* certainly seem intent on showing off your supposed powers of
> psychological inference.
>
> (Need I remind you that psychology is a pussy profession.)
>
>>
>> Mile-for-mile you are correct.
>> But trains are less efficient than a container ship,
>>
>
> I specified "land," which excludes ships.
>
> But another question, energy for energy, would be more efficient
> to offload a container ship in LA, transfer to rail, and then
> transport to NYC.  Or would it be better to sail the same ship
> from LA to NYC through the Strait of Magellan.  (This ship is
> much bigger than Panamax.)

If it's coming from Asia, I would sail around Cape of Good Hope instead.
In a few years, the widening of the Panama Canal or the Nicaraguan canal 
will also address the same issue.

Keep in mind that offloading a container ship means transfer to multiple 
trains.


-- 
Odd Bodkin --- maker of fine toys, tools, tables

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#530261

On Tue, 03 Nov 2015 16:55:26 -0600, Odd Bodkin wrote:

> 
> Old, solved, and pedestrian 
> applications just aren't the kind of thing that get physicists 
> interested
> 

Such applications fall into the realm of classical approximation.
In that realm, they are not actually "solved."

But you are correct.  Most physicists are stuffy and narrow minded
throwbacks that cannot see old things in new ways.

I am not one of those.


> .
> In a few years, the widening of the Panama Canal or the Nicaraguan canal 
> will also address the same issue.
> 

The new canal project will only address some of the problem.  A lot of ships
will still be too large.

But there is hope.  The Northwest Passage is slowly opening to allow
transport all year.  No canals will be needed anymore.  We can all enjoy
the bonanza before the insufferable heat destroys civilization.

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#530217

On Tue, 03 Nov 2015 15:00:01 -0600, Odd Bodkin wrote:

> 
> It's the attention that's really craved, not that the problem 
> is really all that interesting.
> 

What could be the problem, Oddball?

It seems that you taking a lot of extended coffee breaks and three-hour
lunches.  Doesn't that detract somewhat from the construction of fine
toys?  Your next batch of 3500 is likely falling way behind schedule.

Maybe your enterprise is suffering from a slack in sales?

If that's the case, serious attention to some form of product promotion
should be in order.

Maybe you are simply delegating the work of manufacture to underlings
and apprentices of the trade?

Nah.  The pride of a fine craftsman would never permit that.

But it's good to know that you are spending your valuable leisure time
contributing to sci.physics rather than squandering it on YouTube
and Cheetos.

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#530260

On 11/3/2015 3:31 PM, Fabian Russell wrote:
> On Tue, 03 Nov 2015 15:00:01 -0600, Odd Bodkin wrote:
>
>>
>> It's the attention that's really craved, not that the problem
>> is really all that interesting.
>>
>
> What could be the problem, Oddball?
>
> It seems that you taking a lot of extended coffee breaks and three-hour
> lunches.  Doesn't that detract somewhat from the construction of fine
> toys?  Your next batch of 3500 is likely falling way behind schedule.

:)
I get to call my hours. I work for myself.
Right now I'm working on a dining room hutch and a rocking chair.

>
> Maybe your enterprise is suffering from a slack in sales?
>
> If that's the case, serious attention to some form of product promotion
> should be in order.
>
> Maybe you are simply delegating the work of manufacture to underlings
> and apprentices of the trade?
>
> Nah.  The pride of a fine craftsman would never permit that.
>
> But it's good to know that you are spending your valuable leisure time
> contributing to sci.physics rather than squandering it on YouTube
> and Cheetos.
>


-- 
Odd Bodkin --- maker of fine toys, tools, tables

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#530163

On 11/03/2015 09:38 AM, Odd Bodkin wrote:
> On 11/2/2015 8:05 PM, Fabian Russell wrote:
>> Attention physics enthusiasts:
>>
>> In all of the information that I have encountered about train
>> physics -- and there is not a lot of material available -- the
>> energy required to move a train is calculated by considering
>> factors such a inertia (train mass), mechanical resistance (friction),
>> and air resistance (drag).
>>
>> However, one significant factor is always ignored, and that is
>> the rotational energy of the wheel sets.
>>
>> Why?  What is the reason for omitting the rotational energy?
>>
>> In the US, a train wheel is very nearly 1 meter in diameter and
>> has a mass of 1000 kg.  The rotational energy for one wheel is
>> then 1/2 * I * w^2.  At 60 mph (27 m/s) speed, the energy is 179862
>> Joules.
>>
>> At 4 wheel sets per car (8 wheels) with an average train containing
>> 100 cars, the total rotational energy of the wheels is a whopping
>> 143889600 Joules = 144 megajoules.
>>
>> Yet this energy is ignored.
>
> I don't know that it's ignored, but let's put those large numbers in
> perspective.
>
> Let's compare the rotational kinetic energy of the wheels to the
> translational kinetic energy of the wheels.
> w = v/r, and for a disk wheel, I = (1/2)m*r^2.
> So the rotational KE = (1/2)(1/2)m*r^2 * (v/r)^2 = (1/4)mv^2. The
> rotational KE of the wheels is thus half the translational KE of the
> wheels.
>
> Now we can compare the translational kinetic energy of the wheels to the
> translational kinetic energy of the train as a whole.
>
> As you say, 800 wheels on a 100-car train has a mass of about 800 metric
> tons. But the mass of a fully loaded train is about 10,000 metric tons.
> So the translational kinetic energy of the wheels is about 8% of the
> train's translational kinetic energy, and the rotational kinetic energy
> of the wheels is then about 4% of the train's total kinetic energy.
>
> Not insignificant, but not huge either.

Except that train wheels are closer to hoops than disks which could 
increase the value by a factor of almost two. Plus, trains also travel 
unloaded at which time the wheel inertia could become very significant.

OF course all you need to do is install titanium wheels and you much 
reduce the problem. (Talking like a Lib "idea man" now) I'll let 
"railroad men" work out how to pay for them.

-- 

       ___           ___           ___            ___
      /\  \         /\  \         /\__\          /\  \
     /::\  \       /::\  \       /::|  |         \:\  \
    /:/\:\  \     /:/\:\  \     /:|:|  |     ___ /::\__\
   /::\~\:\__\   /::\~\:\  \   /:/|:|  |__  /\  /:/\/__/
  /:/\:\ \:|__| /:/\:\ \:\__\ /:/ |:| /\__\ \:\/:/  /
  \:\~\:\/:/  / \:\~\:\ \/__/ \/__|:|/:/  /  \::/  /
   \:\ \::/  /   \:\ \:\__\       |:/:/  /    \/__/
    \:\/:/  /     \:\ \/__/       |::/  /
     \::/__/       \:\__\         /:/  /
      ~~            \/__/         \/__/

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#530169

On Tue, 03 Nov 2015 13:41:47 -0500, benj wrote:

> 
> OF course all you need to do is install titanium wheels and you much 
> reduce the problem.
>

The efficiency of the train depends entirely on the very low ROLLING
FRICTION of steel wheels on steel rail.  Rolling friction is caused
by the actual physical deformation of the wheel and rail material.

Is titanium just as hard, or harder, than the steel alloy currently
used?  If not, then titanium wheels would only produce more rolling
friction.

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#530427

On 11/03/2015 01:53 PM, Fabian Russell wrote:
> On Tue, 03 Nov 2015 13:41:47 -0500, benj wrote:
>
>>
>> OF course all you need to do is install titanium wheels and you much
>> reduce the problem.
>>
>
> The efficiency of the train depends entirely on the very low ROLLING
> FRICTION of steel wheels on steel rail.  Rolling friction is caused
> by the actual physical deformation of the wheel and rail material.
>
> Is titanium just as hard, or harder, than the steel alloy currently
> used?  If not, then titanium wheels would only produce more rolling
> friction.

Actually if you read some of the literature on the internet from people 
who sell train rails and wheels, you see that it's not that simple. 
(nothing in life is ever as simple as the people on the INTERNET say)

What they talk about a lot is the relationship between the hardness and 
wear. They want the wheels to wear and not the rails (I presume because 
it's easier and cheaper to replace wheels rather than rails). So there 
is this highly complex economic relationship between ALL the factors 
including wheel inertia, wheel rolling losses, metal wear and probably 
much more.

You know, all the things that Boinker never thinks about when he's using 
his "logic" to "prove" some minor point and being completely wrong about 
it.

When simple mindless physics is tried to be applied to some technology 
that has been the subject of economic trial an error for decades if not 
centuries, the answer you get is almost certain to be wrong.

-- 

       ___           ___           ___            ___
      /\  \         /\  \         /\__\          /\  \
     /::\  \       /::\  \       /::|  |         \:\  \
    /:/\:\  \     /:/\:\  \     /:|:|  |     ___ /::\__\
   /::\~\:\__\   /::\~\:\  \   /:/|:|  |__  /\  /:/\/__/
  /:/\:\ \:|__| /:/\:\ \:\__\ /:/ |:| /\__\ \:\/:/  /
  \:\~\:\/:/  / \:\~\:\ \/__/ \/__|:|/:/  /  \::/  /
   \:\ \::/  /   \:\ \:\__\       |:/:/  /    \/__/
    \:\/:/  /     \:\ \/__/       |::/  /
     \::/__/       \:\__\         /:/  /
      ~~            \/__/         \/__/

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#530439

On Wed, 04 Nov 2015 18:08:16 -0500, benj wrote:

> So there 
> is this highly complex economic relationship between ALL the factors 
> including wheel inertia, wheel rolling losses, metal wear and probably 
> much more.
> 

Sure there are some complications.  But I cannot ever imagine that the
prime factor would be anything other than hardness and rolling friction.

I have two hand trucks, similar to the lower left of the examples
on this page:

http://adamsindustrialsupply.com/HandTrucks.html

One hand truck has pneumatic tires (inflatable), and the other has
hard solid rubber polymeric tires.

Putting the same very heavy load on both hand trucks, and pushing both
on the same concrete surface, reveals a fantastic difference.  On pneumatic
tires, the load requires tremendous force to push.  With the hard rubber,
pushing the load is nearly effortless.  Unless one has performed this exercise,
it is difficult to even imagine the extreme difference.

So if I were a railroad engineer, I'd say screw all other considerations
and give me hardness.

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#530206

On 11/3/2015 12:41 PM, benj wrote:
> On 11/03/2015 09:38 AM, Odd Bodkin wrote:
>> On 11/2/2015 8:05 PM, Fabian Russell wrote:
>>> Attention physics enthusiasts:
>>>
>>> In all of the information that I have encountered about train
>>> physics -- and there is not a lot of material available -- the
>>> energy required to move a train is calculated by considering
>>> factors such a inertia (train mass), mechanical resistance (friction),
>>> and air resistance (drag).
>>>
>>> However, one significant factor is always ignored, and that is
>>> the rotational energy of the wheel sets.
>>>
>>> Why?  What is the reason for omitting the rotational energy?
>>>
>>> In the US, a train wheel is very nearly 1 meter in diameter and
>>> has a mass of 1000 kg.  The rotational energy for one wheel is
>>> then 1/2 * I * w^2.  At 60 mph (27 m/s) speed, the energy is 179862
>>> Joules.
>>>
>>> At 4 wheel sets per car (8 wheels) with an average train containing
>>> 100 cars, the total rotational energy of the wheels is a whopping
>>> 143889600 Joules = 144 megajoules.
>>>
>>> Yet this energy is ignored.
>>
>> I don't know that it's ignored, but let's put those large numbers in
>> perspective.
>>
>> Let's compare the rotational kinetic energy of the wheels to the
>> translational kinetic energy of the wheels.
>> w = v/r, and for a disk wheel, I = (1/2)m*r^2.
>> So the rotational KE = (1/2)(1/2)m*r^2 * (v/r)^2 = (1/4)mv^2. The
>> rotational KE of the wheels is thus half the translational KE of the
>> wheels.
>>
>> Now we can compare the translational kinetic energy of the wheels to the
>> translational kinetic energy of the train as a whole.
>>
>> As you say, 800 wheels on a 100-car train has a mass of about 800 metric
>> tons. But the mass of a fully loaded train is about 10,000 metric tons.
>> So the translational kinetic energy of the wheels is about 8% of the
>> train's translational kinetic energy, and the rotational kinetic energy
>> of the wheels is then about 4% of the train's total kinetic energy.
>>
>> Not insignificant, but not huge either.
>
> Except that train wheels are closer to hoops than disks which could
> increase the value by a factor of almost two.

Could, if they were in fact closer to hoops than disks. But in reality 
they're not: 
http://patentimages.storage.googleapis.com/US20030079328A1/US20030079328A1-20030501-D00004.png

> Plus, trains also travel
> unloaded at which time the wheel inertia could become very significant.

But then again, so is friction in the axles and so on.

>
> OF course all you need to do is install titanium wheels and you much
> reduce the problem. (Talking like a Lib "idea man" now) I'll let
> "railroad men" work out how to pay for them.
>


-- 
Odd Bodkin --- maker of fine toys, tools, tables

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#530225

On Tue, 03 Nov 2015 15:10:27 -0600, Odd Bodkin wrote:

> 
> Could, if they were in fact closer to hoops than disks. But in reality 
> they're not: 
> http://patentimages.storage.googleapis.com/US20030079328A1/US20030079328A1-20030501-D00004.png
> 

Most wheels are similar to a hoop, but a train wheel is designed, as I
mentioned, to give the bare minimum of rolling friction, i.e. physical
deformation.

So another question:

Is the interior "disk" of a train wheel essential to prevent excessive
deformation?

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