Ponderings

[silentC]

I've been pondering a couple of things:

1. I have some fly traps hanging from my trees. The traps consist of a plastic bag containing a small amount of bait topped with a funnelled lid, which the flies can crawl into but are too dumb to escape from. Ultimately they die of starvation or whatever.

I've had these things in the trees for about 6 or 8 weeks now. Eventually the bait becomes ineffective, so you periodically dispose of the dead flies and re-bait them. However, every time I check them, they are full of live flies.

Knowing how flies reproduce, how do I know whether the flies in the traps now have come from outside, or whether they have been born inside the traps from eggs laid in the rotting corpses of their ancestors? Could there be many new generations of flies being born and dying in these traps with relatively limited output from the outside world? There aren't many flies around, so are they working, or is it just a bad season for flies?

2. When I am riding my bike into a strong head wind, it is quite hard to keep up the pace and I can hear the wind in my ears. When I turn around and ride the other way, at a slow speed, I can feel the wind on my back and hear it in my ears but as I speed up, it becomes very still (depends on the speed of the wind, but usually around say 30kph). If I ride along at that speed, it requires little effort. However if I push on towards 35 or 40, I can once again hear the wind. Does this bring about increased resistance? That is, does it actually become harder to keep up pace with a slower tail wind behind you, than it would if it was perfectly still?

[Grunt]

1. Close the trap and see if you get an increase in flies. Do you see maggots and fly larva?
2. No, you'll get less resistance with any amount of tail wind. I can cruise at 45-50 kph with a tail wind. That is about as fast as I can cruise at due to the gearing on my bike. There is also rolling resistance which will increase with speed regardless of wind direction.

[Bleedin Thumb]

The answer to question one is simple do you or have you ever seen maggots?

The answer two question two is probably that when the sound of the wind drops off (when you are riding down wind) you are approaching the same speed as the wind - like sailing down wind under spinnaker, - relative wind speed is zero. If you go past that speed relative wind speed increases.

[silentC]

I was thinking of the theory of relativity. If you are travelling at the same speed as the wind, then the air is relatively motionless compared to you. If you speed up, you are now pushing through the air, which is moving slower than you, so surely there is an increase in friction? Maybe it's subject to the law of diminishing marginal returns.

Regarding the flies, I haven't inspected the traps that closely, was just wondering as I walked past them this morning...

[Grunt]

There is an increase in friction when you start to ride faster than the wind. There is also an increase in friction as you go faster when there is no wind or a head wind.

BTW, I hate head winds. give me hills any day.

[silentC]

Obviously there are other factors that come into play, including gravity. If all other things were equal, going from 27 to 30 in a 27kph tail wind would require the same amount of effort as going from 0 to 3 on a calm day but that's obviously not the case. I don't have any scientific observations to contribute, it's just one of the dumb things that goes through my head when I'm riding.

At Sydney, there is a tunnel under the airport runway. I used to be able to get up to 80kph in there without a lot of effort and sustain it for about 200m but I could never do that on the flat outside, with or without a tail wind.

[Grunt]

It's rolling resistance as well as the increased friction of the pedals, chain etc.

Now all you needs is that hover bike.

[Felder]

At Sydney, there is a tunnel under the airport runway. I used to be able to get up to 80kph in there without a lot of effort and sustain it for about 200m but I could never do that on the flat outside, with or without a tail wind.

I rode through there once, and also observed how easy it was to get a decent speed up. I figured that all the traffic was creating a movement of air in the direction I was going, hence a tail wind.

[Grunt]

It does do that. I lived in San Francisco for 6 months or so. They've got B.A.R.T. (Bay Area Rapid Transit) and when you were standing on the platform, a hug rush of wind would always preceded the train.

[Felder]

They've got B.A.R.T.

a hug rush of wind would always preceded the train.

Sorry.

[Bob Willson]

I've been pondering a couple of things:
Knowing how flies reproduce, how do I know whether the flies in the traps now have come from outside, or whether they have been born inside the traps from eggs laid in the rotting corpses of their ancestors? Could there be many new generations of flies being born and dying in these traps with relatively limited output from the outside world?

Put a small amount of really cheap red wine in the bottom of the fly trap. The flies will drink it, become inebriated and drown in the wine.

[Rossluck]

Obviously there are other factors that come into play, including gravity. If all other things were equal, going from 27 to 30 in a 27kph tail wind would require the same amount of effort as going from 0 to 3 on a calm day but that's obviously not the case. I don't have any scientific observations to contribute, it's just one of the dumb things that goes through my head when I'm riding.

At Sydney, there is a tunnel under the airport runway. I used to be able to get up to 80kph in there without a lot of effort and sustain it for about 200m but I could never do that on the flat outside, with or without a tail wind.

[Bleedin Thumb]

Rossluck seems to have siad it all, so I am left speechless.

[Grunt]

It's a pity that Rossluck isn't this successful more often.

[Rossluck]

It's a pity that Rossluck isn't this successful more often.

Sorry fellas. SWMBO downloaded this virus buster thing that has turned our PC into a nightmare. It basically checks every page you open to let you know "it's safe" and it keeps freezing. It's sending me mad (well, madder). It's slowed the computer down to something almost unusable.

I didn't even know that it had send the reply to this thread, and that it had deleted what I had written. But since you have expressed a desperate desire to hear what I have to say (thanks Grunt) , I'll repeat it.

What Silent was saying reminded me of canoeing when you come across "dead water", in which you paddle like crazy and don't seem to get anywhere. I'm thinking that the answer to the question is turbulance: i.e, going through the "air curtain" between the tail wind and the relative bike speed, but that's just a guess.

I'll try again