How a fly can stop a train

[spazman]

Best way a fly can stop a train is to choke the driver to death. I dunno about quantom physics (who does?) so i'll leave that well alone.

[bertie]

Smelly kilaf

[Galant]

Whilst an interesting conundrum, the fact is the train obviously does not stop - if it did - there would be a lot of people inside who'd all have their rear ends on their minds.

Seems to me a lot of people forget about mass - as though the fly and the train exerted equal forces.

How about a train which hits something stationary on the track. That object is already stopped, when the train hits it, it doesn't stop. It momentarily encounters the force exerted by friction (holding the object to it's position), the train's greater force then sends the object flying.

I don't know what I'm talking about.

[Ping]

Hmm, Seems to me that the fly as a whole would never actually stop moving but would merely change direction ( and shape) as the front part of its anatomy would have reversed direction while the rear is still moving forward. To class any cellular particle of the fly as having stopped whilst changing direction you would have to measure that in the sort of time frame that would render movement by the train immeasurable in the time frame allowed and as such you reach the limitations of our inability to measure the time taken to reverse the direction of travel of the fly

[myth]

DAM YOU ALL! I now have a massive migrain

There is no fly! At the moment of impact there will be no fly! Just body parts! And to complicate thing alitle more in this thread what if the frount of the train is a bullet noise? It (the body parts) are now still moving in the same direction but still going forward as it spreads out!

[willieleafe]

Hey guys.. first off I didn't do any physics or anything at college / uni, so forgive me if this is a stupid question. However, I was wondering, if the fly is on the train, would it move with the train, just by trying to hover? Or would it stay still (reletive to the earth).

[Aez]

[TAKTAK]

Hey guys.. first off I didn't do any physics or anything at college / uni, so forgive me if this is a stupid question. However, I was wondering, if the fly is on the train, would it move with the train, just by trying to hover? Or would it stay still (reletive to the earth).

this is an old thread matey...

but i think because the air inside the train is moving with the train... the fly is manouvering in the air, therefore moves with the train

[Whiternoise]

I'm more amused by the number of people i've never heard of posting in this thread

[chicken]

Ah I thought there was something odd about it, didn't cross my mind to check the date!

Just to throw another angle in... Ping mentioned the fact that part of the fly would be stopped whilst other parts were still moving and going down to a cellular level...

If the fly was classed as just a bunch of atoms, then could the fly's atoms hitting the train's atoms stop them briefly, until the rest of the mass of the train catch up and propel the fly forwards? This would not involve the train stopping, but rather a very small portion of it's atoms stopping for a very very brief period of time.

Or to go along the lines of "What the bleep do we know?" would the fly's atoms ever even come into contact with the train's atoms?

[schmunk]

It's not the first time I've started reading a thread then seen the name 'Deckard' and realised that I'm watching Indiana Jones and the Thread of Old...

[chriswood_7]

Surely the fly could stop the train depending on how much energy it had compared to the train. You could probably work out what the relative mass of both are, and then work out what speed the fly would have to travel at if it was to stop the train.

But then of course it would probably be something like 100000mph (the flies wings would come off and he would burn his nose at that speed)

[Mblaster]

Surely the fly could stop the train depending on how much energy it had compared to the train. You could probably work out what the relative mass of both are, and then work out what speed the fly would have to travel at if it was to stop the train.

But then of course it would probably be something like 100000mph (the flies wings would come off and he would burn his nose at that speed)

It wouldn't stop the train no matter how fast it went, it's like shooting the train with a gun, it'll just go through the train as the train itself isn't strong enough to sustain the force needed to stop it on such a small area.

[Whiternoise]

Just work out the momentum of the train and the momentum of the fly (roughly) and you can work out what the energy imparted to the fly is - of course you'd need to know the intial and final velocities of the fly though.

One would assume it would be smeared across the windscreen or it would simply be caught in the slipstream and wouldn't collide in the first place.

If it collided, then the train would simply decrease in momentum by the same amount that the fly had when it crashed into it. The train has stopped for an arbitrary unit of time, but it's not that simple, it's the same sort of thing as measuring the width of an infinitely small line. Another view is that if you imagine the front of the train to be a sort of lattice..

then it'll look something like this (excuse the ASCII art)

|
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| o <- the fly hits the train
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/
|o <- the metal buckles by a tiny amount, and elastically deforms
\
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|s <- dead fly
|s
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