Okay prepare yourselves for the statement of smartness:
"in the real world, things the size of atoms or greater cannot change velocity instantaneously. This means that on whatever level you think of it, the fly/water/water molecules are stopped (ie - 0 velocity, not 0 acceleration) for a short amount of time.
When the fly is stopped, it still isn't attached to the train, it's touching the train and collapsing but it has a different velocity because it isn't attached." - my friend Russell
So I am wrong, and Ark was right. And the windshield does bend. But the train doesn't stop.
Originally posted by Coconut😏 No, I'm just kidding. I only knew because I asked my dad anyway.😉
Okay prepare yourselves for the statement of smartness:
"in the real world, things the size of atoms or greater cannot change velocity instantaneously. This means that on whatever level you think of it, the fly/water/water molecules are stopped (ie - 0 velocity, not 0 acceleration) for a short amount of time.
When the fly is stopped, it still isn' ...[text shortened]...
So I am wrong, and Ark was right. And the windshield does bend. But the train doesn't stop.
I read many posts here but was too lazy to read them all. Did anyone mention the point of view thingy yet?
From the flies point of view the fly is standing still all the time. Only the train is moving and even we (the observers) are moving.
So I guess when the fly hits the window, two objects (fly and train) become one (fly-on-train). So since the object fly doesnt exist anymore, it cannot have stopped the train.
Okay, since that was a rather boring solution here are some calculations:
- v is the speed of "fly-on-train" after the hit
- object 1 is the train, object 2 is the fly, so:
m1 = mass of train = (around) 20 tons= 20,000 kg
m2 = mass of fly = 10 grams = 0.01 kg
u1 = speed of train = 200 km/h = 55.56 meters/second
u2 = speed of fly = -20 km/h = -5.56 meters/second (negative
because opposite direction)
v = (m1*u1 + m2*u2) / m1 + m2
v = 55.55552499 m/s
In other words, the fly reduced the trains speed by 0.000030555 m/s. Amazing! 🙄
PS: There are some air fields and winds and all that stuff around the train which I didn't care about. If anyone knows how to calculate that, feel free to do so 😛
Originally posted by crazybluecarrot...
I read many posts here but was too lazy to read them all. Did anyone mention the point of view thingy yet?
From the flies point of view the fly is standing still all the time. Only the train is moving and even we (the observers) are moving.
So I guess when the fly hits the window, two objects (fly and train) become one (fly-on-train). So since the obje ...[text shortened]... e train which I didn't care about. If anyone knows how to calculate that, feel free to do so 😛
Originally posted by crazyblueTEN grams for a fly, man, that is one biga$$ fly!
I read many posts here but was too lazy to read them all. Did anyone mention the point of view thingy yet?
From the flies point of view the fly is standing still all the time. Only the train is moving and even we (the observers) are moving.
So I guess when the fly hits the window, two objects (fly and train) become one (fly-on-train). So since the obje ...[text shortened]... e train which I didn't care about. If anyone knows how to calculate that, feel free to do so 😛
you realize that is about one third of an ounce? 1 Oz=~28 grams.
I'm thinking the fly weighs about one TENTH of a gram so your
calcs would be off by an order of magnitude, also the velocity part
isn't right because you have to use kinetic energy not just velocity
so it would be MV^2 of train minus MV^2 of fly. You didn't square here.
Also I think the kinetic energy of the train will be a lot more than
20 tons, even if the engine only weighs that much because of the
coupling of the rest of the train, but that is a coupling tha happens
at the speed of sound in metal, whatever that is, I imagine it must
be a lot faster than the speed of sound in air but there would be
a fraction of a second of the engine's kinetic energy being the only
energy to consider. So in that sense I guess the rest of the train
is out of the picture.
Originally posted by CoconutSo you are saying that the fly isn't at any velocity at any given time?
I don't believe you.
Consider a position graph in the parabolic, and a graph in the absolute value. To get the velocity at any point, we must find the slope of the tangent to that graph at that given point. Parabolic? Easy, the velocity (slope) will slowly become less positive, zero for an instant, then more negative. As if a ball were thrown into the ai ...[text shortened]... till just see a point. Like this: ^
I will consult other, smarter people on this one as well.
Originally posted by sonhouseAbout the weight of train and fly: I just wanted to show that the speed difference of the train before and after the hit is so small that it doesnt matter. So if you take a smaller weight for the fly and a bigger weight for the train, the speed difference would be even less.
TEN grams for a fly, man, that is one biga$$ fly!
you realize that is about one third of an ounce? 1 Oz=~28 grams.
I'm thinking the fly weighs about one TENTH of a gram so your
calcs would be off by an order of magnitude, also the velocity part
isn't right because you have to use kinetic energy not just velocity
so it would be MV^2 of train minus MV^ ...[text shortened]... quare here.
Also I think the kinetic energy of the train will be a lot more than
20 tons [...]
About squaring v: Why would you do that? It isnt mentioned anywhere that the train or the fly are accelerating. To me it seems to be a common unelastic hit (I hope thats the correct english name for it) which requires the formula p = m*v (impulse = mass * speed).
For unelastic that hit with 2 objects, the formula is as i posted above.
Maybe im completely wrong. Try to convince me 🙂
Originally posted by BowmannIf the fly managed to some how get into the cockpit, and proceeded to bite the driver. And if the driver suffered a severe Anaphylactic reaction to the bite. It would force him to let go of the dead mans controls, thus stopping the train. Therefore hypothetically it is possible for a fly to stop a train but realistically it is unlikely to happen.
A little lateral thinking can go a long way...
Originally posted by crazyblueThe correct English term for it is inelastic collision. 🙂
About the weight of train and fly: I just wanted to show that the speed difference of the train before and after the hit is so small that it doesnt matter. So if you take a smaller weight for the fly and a bigger weight for the train, the speed difference would be even less.
About squaring v: Why would you do that? It isnt mentioned anywhere that the tr ...[text shortened]... 2 objects, the formula is as i posted above.
Maybe im completely wrong. Try to convince me 🙂