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There are some good ideas here about using rails to gain efficiency (lower
the amount of wasted energy). Railroad efficiency is high because of the
use of steel wheel on steel rail. The rolling resistance is extremely low.
Also, accelerations are very low because the coefficient of sliding
friction of steel on steel is so low. It would make no sense to try to
attempt a jack rabbit start with a train because the locomotive's wheels
would just spin uselessly. Trains tend to run at a single steady speed -
very unlike automobiles.
A big savings can be had by replacing automobile lanes with rails. Cars
could communicate with switches by radio or wi-fi, so one could
theoretically have the same flexibility of travel as on paved roads.
Proximity sensors on the cars could elimiate a lot of the speed changes
that occur when one car slows down abrubtly to match the speed of the car
it's following - leading to the dreaded "traffic wave" and the resulting
stop and go traffic. Rails would also stop drunks from wandering out of
their lanes - reducing the annual carnage on paved roads.
Rails tend to flex most when the locomotive passes - modern rail and
roadbed flexes little due to the train itself - I'm not sure that piezo
schemes would be worth it - or even disirable because of the bump that
would occur with a high speed passage of a piezo with any significant
compression.
This leads to the commonly discussed idea of Mag-Lev. They are not really
more efficient that steel wheel on steel rail - it's like the difference
between an efficiency of 0.999 and 0.9999999. Granted, the Mag-Lev has
less friction - but the difference is miniscule. The only good feature is
that you don't have a locomotive belching out black smoke - the power
savings are minimal and not worth the investment in the system.
Sorry for wandering off topic - but it seems that it's better to save
energy than to come up with this hare-brained way of generating energy
using piezo effects.
Bob at PC
-----Original Message-----_______________________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of John Clement
Sent: Monday, February 28, 2011 12:31 PM
To: 'Forum for Physics Educators'
Subject: Re: [Phys-l] [ncnaapt] another crackpot idea from the
California legislative assembly
I agree that the first law is not the whole story, but some of the
schemes
mentioned here do have some first law components that make them not so
attractive.
Capturing the air flow from passing cars will likely produce a back
wave
which would increase air resistance for the cars. In which case the
air
turbines are robbing energy from the autos. The piezo electric idea
means
you now have springs under the roadbed which will likely make it more
elastic. This would again would probably decrease auto efficiency.
The
audio energy source would have negligible interaction, but also
negligible
power output. You have to find schemes which will not rob usable
energy
from one source to power another source. The result of doing that is a
decrease in usable energy due to the second law.
Indeed the devil is in the details. There are much larger sources of
energy
which are more easily tapped such as wave motion. Thermal and light
energy
from the Sun has been tapped in many ways. This is a case of wasting
money
to look at a very small source of energy which is extremely expensive
to
tap. Actually you probably would get more energy from engine shake
than
from roadbed deformation. How about developing more efficient road
surfaces? Does soft blacktop waste more energy than bare concrete?
Both
should be better than gravel, and certainly better than sand.
A simple way of looking at this is to compare railroad efficiency with
auto
efficiency. Both deform the roadbed, but the railroads are much more
efficient in operation. So the amount of energy absorbed by roadbed
deformation is not a large percentage of the energy expended by the
engines.
If you were to try piezo generation first do it with railroad tracks.
They
have definite points where it is easy to insert the piezo generators.
You
can actually see the tracks deform, but how much do non elevated
roadbeds
deform? The swaying of bridges probably has more energy than the
roadbed
downwards deformation, "Galloping Gertie" excepted. Of course Gertie
was
wind driven.
Incidentally the roadbed idea is generating the energy at the wrong
time.
It is needed when people are at work or home, not when they are
commuting.
The legislature has slipped a decimal point because they can't figure
the
amount of energy and the expense of this scheme. Who came up with it,
and
who is paying them for it?
John M. Clement
Houston, TX
form of
The question that needs to be asked, and I don't know the answer with
respect to Piezoelectric energy generation, is whether the energy is
captured energy that would escape into the environment if it were not
captured by the piezoelectric generator, or if it is a more direct
energy generation, like a generator.wind
For example, you could set up wind turbines that would capture the
produced by passing cars, or large microphones to capture the soundany in
generated by the passing cars. Neither of these methods would cost
gasoline consumption because they are capturing wasted energy. Notires
violation of the the First Law. I can think of many others, such as
capturing the heat that rises from the road, or heat generated by the
tires on the road. Some, like capturing the heat generated by the
on the road, might actually improve the gas milage of the cars.whole
A naive application of the first law is not always going to tell the
story. Hell, that's why hybrid cars are more efficient! Look to the
Second Law!
_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l