biglee

fly is travling directly towards a train doing 70mph,

now when the fly hits the train it MUST by the laws of science first stop before it can go the other way(oposite direction)

but the fly obviously doesnt stop the train, so how does this happen???

is it a science cock up?

S1

If it's a BR train then the laws of physics cease to apply, thats why they can't run when it's the wrong type of snow etc...

PhilM

It does stop, instantaneously as it hits the front of the train, its velocity will go from whatever forward speed it had, down to zero, and then accelerate up to the velocity of the train (in the other direction).

dave cos4x4

iTrader: (5)

biglee

but the train is a constant, so how can it stop at all, unless a bounce period happens

hit-bounce-stop-hit-travel..........ect

Mr Sam

it stops then kinda explodes in a smeere in several directions

RSeb

it stops for like a millionth of a pico second before changing direction you nutter!!

MB7201

Yep, it will be zero for an infinately small amount of time relative to the ground

biglee

so the train stops??? how can that happen.....passengers would all die

RSeb

no the fly not the train!!!

tregmatt

iTrader: (3)

well i am not going to lose any sleep over it

THE RADMAN

iTrader: (2)

Project ST

Train will slow down by an amount inversely proportional to the ratio of the weight of train to fly - only a tiny (almost immeasurable) amount. But it will slow down - and then speed back up pretty much instantly.

Bigger the fly, the more the train slows down.

Mr Sam

so what happens if the train hits say a swarm of bee's

biglee

yes i understand the resistance theory, what im asking is of a complete direction change, directly opposite the way the fly was going, it must stop to change direction it is imposible to go the oposite way on the same path without first stopping, so now we must say the train must stop...or we all fall into a big black hole and the universe eats itself...

Project ST

Project ST

Everything is relative - if the fly is "stopped", that only means it's not moving in relation to the ground - it's still moving around the sun in the solar system.

Easy way to think about it:

If the fly's doing 10mph and the train's going 70mph in the opposite direction, that's EXACTLY the same as if the fly is doing 0mph and the train's going 80mph - the fly still gets hit by the train exactly as hard, but there's no "stop" - it just accelerates almost instantly up to 80mph.

[edit - stupid fucking apostrophes ]

biglee

ok so this is mt theory....what you think

There's a short period of time when the front end off the fly has changed direction and is travelling with the train, and the back end of the fly is still moving towards the train. That's during the s of splat. The train windsceen is slightly elastic and takes up the reciprocal movement.

cossiematt

Ever thought about when you see people shooting bullets from a gun straight up in the air?

That bullet accelerates upwards, stops, then accelerates back down at the same rate it went up.

So if it hits you on the way back down its no different than if the barrel of the gun was pressed against your head. i.e. it would hurt



Whats the last thing to go through a flys mind when it hits the windscreen?????????




Its arse

Graceland

Has anyone asked the fly what it thinks on the subject?

Just before its arse impacts it's head is a nice time to ask

biglee

ive got it....

ok so what happens is the fly will stop and go the other way micro seconds BEFORE the train hits it...it does this within the cushion of air that the train pushes in front of it.... then...SPLAT, but its allready going the correct way and doesnt have to stop a train....

got to be the only logical answer...

Dan B

Newtons 2nd Law: "The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma."

The fly will have a mass of, say, 10 grams, and is travelling at, say, 2 metres/second. The train will have a mass in the region of, say, 100 tons, and is travelling at, 30 metres/second (precisely 67.014388489208633093525179856115 mph).

Convert 100 tons into kilograms --> 100,000kg.
Convert 10 grams into kilograms --> 0.01kg

Therefore, the fly has an instantaneous Force of 0.02 Newtons, and the train has one of 3,000,000 Newtons.

Result: the fly splats on the windscreen, the new speed of the train is calculated by comparing before/after momentums.

Momentum before collision = (100,000 * 30) - (0.01 * 2) = 2,999,999.98 Newtons

Momentum after collision = (100,000.01)V Newtons (where V is the common velocity)

Momentum before collision = Momentum after collision
--> 100,000.01V = 2,999,999.98
--> V = 29.9999968000003199999680000032 metres/second
--> V = 67.014381341007909064676719431609 mph

So, to compare, the speed of the train decreases by 0.0000071482007240328784126618mph in the impact......not sure that's a change in speed I'd notice quite easily, really!







And yes, I was bored!

BlueSmoke

Eh? Why the hell would the train have to stop? It obviously has way more momentum than the fly and does not stop. The fly stops for a nano second on impact before changing direction whilst stuck to the front of the train.

This thread is ridiculous!

Mr Sam

my throat and sides hurt im also developing a headache

biglee

thats how much the train slows after the fly has hit it....
and very well done.....

but it still does not explain a pico second stop before going the other way....

Redeye Jedi

Why do u need to know this?

biglee

First off, from Newtonian physics, there is nothing that says the train must be stationary at any time during the collision. Instead, physics says that the train must only decelerate as a result of the collision, such that the forces on the fly and the train are equal, as per Newton's 3rd Law, "for every action (force), there is an equal and opposite reaction (force)." Since the forces on the fly and the train are balanced, and since force equals mass times acceleration (Newton's 2nd Law), the negative acceleration (deceleration) of the train is tiny because of its tremendous mass. Actually, the splattering demonstrates that this is a completely inelastic collision, and for any collision, the conservation of energy is the overriding rule - K.E.fly + K.E.train = K.E.fly+train + Esplat (heat energy lost to smooshing the fly) - though the resulting deceleration is still miniscule unless the fly's velocity is sufficiently great to give it significant kinetic energy (K.E. = one half mass times velocity squared).

biglee

because i want to know.....

i guess im just curious

Redeye Jedi

Fair enough!

pee vee

As stated above, the train will not stop (unless the fly is superman )

it will have a tiny decrease in speed, again as stated above.


remember energy cannot be destroyed only change form,
so If your theory of the train and fly stopping momenterily
as they collide
where has the energy gone!? that would cheat the laws of physics.
(if i remember rightly from all them years ago at school )

NUTTIN RILLA

I used to think of that alot until my brain nearly exploded Its the same as a piston in your car, at some point that piston has to stop at the top of the block before it goes back down again hard to think about isnt it

my head hurts again

dojj

iTrader: (3)

as dan says, the mass of the train so massivly outwieghs the mass of the fly the effects are imeesurable really

as for the where the energy goes, it's released as heat, thats why fly splatter is so hard to remove from the screen (also the cooling effect of the air moving out of the way of the train acts to disapate the heat caused by the colission

Ginge !

eiherway the fly is fooked

S1

Thats all well and good but whats the last thing that goes through a fly's mind when it hits the windscreen?



















Its back leg's


I'll get me coat

L33 BYT

Impressive stuff

foreigneRS

this has to be the most stupid thread ever posted

biglee

cheers....BIG EARS

Phil

iTrader: (1)

The laws of Physics are only guidelines and only apply in a contained environment.

If you had a hig enough speed camera, you would see that when the fly hits the train, the head of the fly (assuming that hit first) will be travelling in the opposite direction to the tail of the fly for a split second. Now thats got to hurt

RWD_cossie_wil

iTrader: (9)

however, if the fly had a velocity of 300,000,000 metres per second, its momentum would be exactly equal to the momentum of the train - and theoretically it would stop the train instantly as the two opposing forces forces would balance exactly

Porkie

iTrader: (1)

Totally wrong in my opinion