Kinetic rope again..

Well, not much of an argument being as you said pretty much what I said but with lots more words ;-)

Heh, I can imagine a vehicle minus its axles shooting out of a hole!

Sounds like a good excuse for a demo!

What's to stop you splicing in two safety tag lines with eyes?

AJH

Lack of experience and a worry that I might create a weak point!

I suppose if I was that concerned about the tow points giving way there's nothing to stop me using a bridle either in the conventional way, or to loop the main attachment point to a secondary one. Then I could have a mexican-style bola whirling across the site ;-)

On or around Mon, 31 Mar 2008 22:49:16 +0100, andrew heggie enlightened us thusly:

which is Kinetic energy. Argh, now I've got to remember my physics properly...

The essence of the thing is the energy available and the amount of stretch in the rope makes no difference to that if the speeds are the same. The only thing that the stretchy rope does is make the transitions more gradual. By doing that, you can apply more energy (i.e. operate faster) but you should always be aware that by doing so you have a system with more energy in it, and more potential for harm if something breaks.

Also, the fact that the force builds slowly with the stretchy rope doesn't alter the load placed on the attachment points.

It does change the tow vehicle's resistance to the movement due to its own inertia, which is not such an issue with a proper kinetic rope as it builds up the pull slower, this also allows the stuck vehicle to potentially start moving before you reach a maximum pulling force, whereas when you yank it with a normal rope you basically go from no pull to max in a very short time.

I think you confuse energy with force, what you need to start moving the dead vehicle is force enough to overcome the resistance of its weight in the mud. If that force isn't available from the tractive effort of the towing vehicle then you have to find a way of applying more force. What the kerr does is to allow the towing vehicle to convert its kinetic energy into potential energy in the rope. As I said this energy is the area under the graph of force times rope elongation, this determines how much pull and for how long the rope will deliver that pull (plus of course the continuing tractive effort from the towing vehicle).

Sorry that went past me, I'm assuming a stationary, stuck, vehicle and a moving towing vehicle.

No if that were all you wanted you'd just be using the rope as a shock absorber. Consider a spring fishing scale when you slowly attach a 2kg fish to it it reads 2kg, add that fish to the spring at zero and drop it and the scale initially overshoots somewhat, its the energy in the overshoot that the kerr is making use of to add to the tractive effort of the tow vehicle.

Yes it does because the rope is able to deliver an impulse to the towed vehicle in addition to the tractive effort of the towing vehicle.

When you do the same thing with a less elastic rope the energy still has to be dissipated, often in the plastic deformation or breaking of a component.

AJH

try googling "snatch straps aus"......