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Discussion in 'OT (OFF Topic) Forums' started by Dieselman, Aug 15, 2008.
Help my flask is broken and I dropped my pen over the edge of the platform !
Could be I'll have to get a photo!
Certainly nowhere near that magnitude of difference.
Rolling resistance is just a different form of static resistance.
Thats as maybe. But that table doesn't have figures for the interaction of rubber against tarmac. And the whole point of those two materials is that they DO provide good grip under most conditions. If that were not the case then we would all be skidding around uncontrollably. I am unconvinced that COF is the same beast as RR. Similar, but different.
RR depends on so many things, not least being materials in contact, bearing quality, wind resistance (speed), gradient and weight to name just 4 or 5.
If the drage force on the train is proportional to speed squared, then the power requirement is proportional to speed cubed, hence
So, 100mph would be my answer.
Train spotters.....yawn, yawn.
And your answer is.?? Go on..
Pray tell...............I am waiting to go to bed............
Ok..I was letting as many as wanted to have a go.
The answer is 100mph as correctly computed by NumberCruncher.
With any mode of transport through air you need twice the power to go 25% faster, four times the power to go 50% faster and eight times the power to go twice as fast.
So to travel at 100mph in a car requires eight times the power as traveling at 50mph as by then rolling resistance and drivetrain friction are a fixed element.
The acceleration difference is significant though if a power-car fails.
I got a headache been on a train from Liverpool St to Ipswich. I need to get to bed and have a good sleep.
How come it took one and a half hour between Ipswich to Liverpool St but 1 hour and 10 mins between Liverpool St and Ipswich, god knows the answer. The train slow down at Marks Tey in case someone might jump on the track in front of the train.
The train was definitely travelling at 100 mph past Chelmsford where I can see A12 parallel to the rail line overtaking a Mondeo travelling at 80 mph or more?
I remember when it arrived at Liverpool St, I had a quick glance on the leading engine said max speed 100 mph not 125. The 125 are the one traveling between Aberdeen/Edinburgh and King X. The 125 between Euston and Nottingham doesn't even travel at 80mph. There are no more 125 in this route now, something else and very new and fresh.
Someone started a website.................http://ihatenationalexpress.blogspot.com/
Rubber Asphalt (Dry) 0.5-0.8
Rubber Asphalt (Wet) 0.25-0.0.75
Rubber Concrete (Dry) 0.6-0.85
Rubber Concrete (Wet) 0.45-0.75
Steel (Mild) Cast Iron 0.23 0.183 0.133
Steel Cast Iron 0.4 0.21
Steel (Mild) Steel (Mild) 0.74 0.57 0.09-0.19
Steel(Hard) Steel (Hard) 0.78 0.42 0.05 -0.11 0.029-.12
The initial comment was about steel being 1000 times less resistant to motion.
The biggest difference between the two is the enormous mass disparity. The inertia/momentum of a train is enormous in comparison to a car, and similarly a large ship in comparison to a train ( a train will travel much further than a car because of this; it also takes many miles to stop a cruise ship or an oil tanker travelling at twenty knots.)
Sorry I put the link in now.
>> how do they ensure both engines are working at the same output?
It doesn't matter - as these are diesel electrics, there's no direct drive from the engine to the wheels, and so, if one power car fails, the other one can still drive the train, whether it's pushing, or pulling.
In a typical way, calling these trains 125s is typical British understatement. Without a speed limiter, they would hit about 150mph, and in-service, based on some measurements I took from the train's equivalent to the ABS system while working on a project, they are limited to about 132.
I must confess to having done the quick calc I posted above once before - while crawling back home from London with one failed power car! The acceleration is much much slower!
Next time someone is on an intercity, take a GPS with you and measure the speed. I took one from St Pancras to Paris Nord and it was amazing to see how quickly you zip out of the UK in realtime