Funicular railway odd phenomenon

[truckman060473]

At the cliff railway in Aberystwyth, the rail carriage begins its climb up the steep hill. at some point in the journey before half way, you can clearly see that the track gets even steeper. What is most odd is that the cable hauling the carriage, which runs over rollers on the track centre just seems to lie slack on the rollers, when the laws of physics would say that with a carriage of this weight on a gradient this steep would cause the cable to pull taut into a straight line , hence come up a foot or so off the rollers. It can't possibly be true that the cable weight vs the carriage weight keeps it down. I think the vehicle is 6 tons or more

 

[WatcherZero]

If its a heavy steel cable it can appear slack even when under load because theirs a lot of resistance to becoming taut from its thickness if you know what I mean.

 

[jopsuk]

Aye- think overhead power transmission cables. They're under huge tension

 

[truckman060473]

yes, on pylons they hang in the middle due to the weight. this is just the weight of the cable though - it doesn't have a vehicle of 6 or more tons hanging from one end. This is one of those situations where if you built a model of this funicular railway and used materials that had the same ratio of weight between the cable and the towed car, I bet it would make the cable pull taut off the rollers. I can only assume then, that in real life, the change in the angle of ascent although clear to the naked eye, is quite small and will not make the cable pull any nearer to taut than it already is.

 

[jopsuk]

No, on pylons they're tensioned- the cable stills hangs in a catenary curve.

The other one to think about the support cable in Overhead electrification. This too is highly tensioned. the contact cable is then hung from it using the dropper wires to reduce the amount it sags.

The force required to pull a heavy steel cable "straight" would, I'm pretty sure, be beyond the breaking force of the cable. This isn't something that scales linearly.

However, you are correct that the chnage of the angle of ascent is much smaller than you think- even the gradient angle itself is much less than you might estimate.

 

[Mystic Force]

To be taught ie lie in the plane of direction of pulling would require infinite tension.

 

[truckman060473]

so you mean that if two people are pulling at each end of a 6 ft length of string so the string is tight, it is not actually horizontal but bowed (by gravity) by a tiny tiny amount that the eye can't see?

 

[jopsuk]

Yup. Everything "unsupported" gets deflected by gravity