I fully appreciate that, it wasn't me who,was asking the question.
I guess you were deliberately ignoring the inertia of several hundred tons of train in your second example ;-)
--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)
What's to understand about a rate of change of a rate of change? If the first derivative of a function is itself a function of the same variable, then the second derivative *must* exist.
Take your example of acceleration. A body at rest is accelerated uniformly. At t=0, dV/dt=0. At t>0, dV/dt >0. At some vanishingly small time. dV/dt must have changed, hence the acceleration must itself have a derivative.
In Electrical Engineering, we sidestep the issue by using Laplace transform methods.
--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)
Not at all. DC motors develop maximum torque at zero RPM, and acceleration goes as the motor torque at any speed. You just forgot one derivative. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Dunno about that. I've 'plugged' a decent-sized DC motor a couple of times, and I think the torque was even higher under those conditions. ;-)
(maybe one more deep)
velocity is the rate of change of position (first derivative of position wrt time)
acceleration is the rate of change of velocity (2nd derivative of position wrt time)
jerk is the rate of change of acceleration (3rd derivative of position wrt time)
It depends on the controller, or, back in the day, whether the motor was series-wound or shunt-wound. Series-wound motors have a whole lot more torque at low RPM.
It's interesting that the maximum continuous torque an electric motor can produce is proportional to its volume. Due to iron saturation and I**R dissipation, the maximum Lorentz force per unit area on the rotor is approximately constant, but the torque and the perimeter both go as the radius, and the area goes as perimeter times the length. Counting up the powers, that gives a torque proportional to length times radius squared, i.e. to volume. To get more power out of a given size motor, you have to run it fast.
I expect that trains probably use induction motors with variable frequency drive, which makes them behave more like DC motors without the brush problem.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
It depends on the DPDT switch? ;-)
You can get WAY more current than the LRA if you suddenly reverse a DC motor that is running forward, because the back-EMF then adds to the input voltage instead of subtracting. Enough current & torque to literally destroy the motor.
Wow, just like a rental car!
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
I've used it, for bifilar windings. Ratio transformers often went for
11-wire bundles. That would need more colours than I've ever come across from a single supplier.-- Bill Sloman, Nijmegen
That's because you're asking for different colours instead of different colors.
I forgot the smiley. Sorry. :-)
That is why we put brakes on every wheel on every car. So, it then becomes: Jerks. Lots of 'em.
That is what an ohm meter is for. You perform the wire ID BEFORE any terminations are performed.
I thought trains used series-wound DC traction motors and use a resistive pile for regulation.
Entirely possible--I don't know a lot about trains, but I'd be surprised if the reliability advantages of VFDs driving induction motors weren't pretty compelling there too.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Without the stunning off-road capability of the rental car ('mietwagen' in German, which sounds a lot like meat wagon .. der mietwagen ist kaput!)
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
the
rny
It's still labour-intensive. Using round-to-flat cable, would trade off assembly time for winding area, usually a bad deal.
-- Bill Sloman, Nijmegen
MBAs only do one thing. Screw their employers and co workers before they jump to their next company. They can't see anything more than 90 days in the future.
-- You can't have a sense of humor, if you have no sense.
the
resistive pile
The newest models are VFD plus induction motor. The previous generation is AC generators and SCR phase controlled rectifiers feeding primarily series compound wound motors. They desired a bit more torque at high operating speeds (>70 mph / 110 kph). Bullet trains are mostly VFD and induction motors. Or maybe i am full of baloney.
?-)
variable,
Not all functions have derivatives. Thus the first derivative can exist and the second derivative does not. YCLIU
?-)
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