Re: [Phys-L] train stopping distance

["LaMontagne, Bob" <RLAMONT@providence.edu>]

Not to belabor this, but a few numbers to consider:

Typically, it takes about 15 lbs of force per ton to keep a train moving at 60 mph - an overall coefficient of combined resistance of only 0.0075.  A single gallon of fuel can move a ton of freight at that speed about 500 miles. Six gallons could take it across the country. A trailer truck would take 35 gallons per ton to cover the same distance. A typical automobile would take about 50 gallons. Moving tonnage by rail is remarkably efficient.

Given the development and deployment cost of any foreseeable maglev, the cost of maintenance, power to overcome air resistance, and power to keep magnets activated, it is hard to see maglev as cost effective. Of course, one could say the same if railroads did not exist, and the infrastructure had to be created from scratch. But they do exist, and they are efficient.

Bob
________________________________________
From: Phys-l <phys-l-bounces@www.phys-l.org> on behalf of Bernard Cleyet <bernard@cleyet.org>
Sent: Friday, June 24, 2016 4:09 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] train stopping distance

> On 2016, Jun 24, , at 12:38, John Denker <jsd@av8n.com> wrote:
>
>
> The coefficient of friction for steel-on-steel is on the order of 0.5,
> so when you see an acceleration of 0.02 Gee you know they're not trying
> very hard.


If I were the “engineer” of a passenger train, I’d make a quick decision as to the conflicting result(s) of a one g stop and the collision.


bc points out that passengers ina train aren’t using seat belts.


p.s.  Also what about “floating" luggage?



On 2016, Jun 24, , at 12:38, John Denker <jsd@av8n.com> wrote:


Typical fasteners (for holding rails to the sleepers) look to me
like they're designed to constrain movement in every direction
/except/ longitudinal.  There must be ways of transferring
longitudinal momentum to/from the earth, but the details don't
seem particularly obvious.
__________

Despite not having read the references, I’ll …

Intuitively the coefficient of f. steel on wood (in Europe the sleepers are sometimes concrete.) is greater than the steel-steel 0.5.  So the prob. is sleeper movement on (in) the ballast.  There the friction is > 1, I think.  I judge this from the German buildings on sand for gun emplacements.  (gud for vibration isolation also)

— Not a bad science faire project, no? — .
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