The practical side of considering loops as waves: Teaching and Self Improvement

[Merlin]

Graeme

Torsten is right about the reciprocal of frequency (period in seconds). What becomes ridiculous is to try negate basics. The wavelength is in meters and corresponds to the formula indicated by Torsten: good luck for finding a value corresponding to a cast. Anyway wavelength has little meaning in terms of casting.

Again, perseverare diabolicum.

Merlin

[Graeme H]

Both diagrams will be the same though.

This is one reason why I need clarification because the impulse should be in different directions.

Cheers, Paul

One impulse is basically horizontal and the other impulse is basically horizontal. I'll leave it to you to work out which is which.

IMG_5245.JPG (75.7 KiB) Viewed 2064 times

There's your diagram.

Graeme

[Graeme H]

Graeme

Torsten is right about the reciprocal of frequency (period in seconds). What becomes ridiculous is to try negate basics. The wavelength is in meters and corresponds to the formula indicated by Torsten: good luck for finding a value corresponding to a cast. Anyway wavelength has little meaning in terms of casting.

Again, perseverare diabolicum.

Merlin

Knowing that gravity makes the fly line fall allows us to calculate the wavelength in metres after we establish the period. A period of 2 seconds during which we lifted the line for (say) 1 second total front an back means the wavelength is maximum of 9.8 metres minus variables like drag. That's going to vary with length and speed of the cast.

But please remember that physics was never meant to be discussed in this thread. It's about teaching, remember? Of course, this is all too hard to calculate (as Torsten admitted earlier) so just forget I ever tried to help people understand something. It's probably better that you guys think the loop is witchcraft or some sort of physics that's unique to fly lines.

Latin should help expel the demons.

Graeme

[Paul Arden]

Thanks Graeme.

Why do you have the wave propagating at 90 degrees to the “resultant tension”?

Cheers, Paul

[Graeme H]

That is the estimated instantaneous tension at the rod tip during the impulse (the casting stroke). While it's propagating, the tension in the line will change dramatically and variably throughout the line. Where on the line and when in the cast should I try to draw that tension vector for you?

The loop is the largest amplitude (and longest period) wave in the line during the cast. It's principal tension is vertical but we can modify the tension in the line to change it's character, which is exactly why I started this thread.

[Paul Arden]

In the tethered example a transverse wave propagates along the length of the taught line. As you said yourself. No tension no wave.

However you have the wave propagating at 90 degrees to your resultant tension. I was expecting it to be 180. That would be what I would normally consider to be the direction of propagation of a transverse wave.

Cheers, Paul

[Graeme H]

When would you like me to draw tension in the line? At what point in the line? How much tension should I add or remove from the rod tip? What's the line speed and mass?

[Graeme H]

I've shot a video of an experiment for Dirk in which we are measuring tension directly during the passage of a loop along the line. I'd suggest waiting for his results before answering my questions above.

[Paul Arden]

It seems to me that we are trying to fit a square peg in a round hole.

As I drew earlier I believe this is a rough layout of tension in the loop.

Keen to hear more about your experiment.

Cheers, Paul

[Paul Arden]

Propagation of a transverse wave, as you said, requires tension. However the reason the loop falls is not because it is a wave propagating transversely, but because of gravity. It’s gravity that’s the key ingredient here, not tension. That doesn’t make it a transverse wave. That just means we are casting on Earth.

If instead of an unrolling loop we just had a length of line extended and allowed to free fall, it would also fall the Earth. No transverse wave required!

Cheers, Paul