I think what you're suggesting is.... well it's wrong.
The fly doesn't transfer enough momentum to halt the train.
You are drawing on the fallacy that if you choose a moment in time, i.e. the fly hitting the train/train hitting the fly the train seems to be still; as you have stopped time.
This thread is an assault on reason!
Originally posted by Freddie2004This is the problem, Freddie.
At the instant it changes direction, the fly must be stationary and because, at that instant it is also stuck on to the front of the train, the train must also be stationary. Thus a fly can stop a train.
Assuming the fly is a solid object, like a pingpong ball, its whole will
have to reverse velocity in order to change directions, just like when
you throw a ball against a wall (the liquid example simply
demonstrates that the fly, being organic, will do this in very rapid
stages, first the front, then the middle, then the back -- even a rubber
ball will do this, as it bends when it hits the wall).
However, the notion that the train is stationary is fallacious. The
train is never stationary; it may lose an infinitessimal amount of
velocity as the fly strikes it, but nothing more than that.
What you are describing is one of Xeno's paradoxes. He observed
that motion is made up of an infinite number of stationary positions,
like frames in a movie reel. But, of course, just because the picture
of a discrete moment in the travel of an object appears stationary,
it certainly isn't. Otherwise motion, itself, is a paradox.
Nemesio
Originally posted by NemesioBefore you completed writing that, you had to write half of it...
This is the problem, Freddie.
Assuming the fly is a solid object, like a pingpong ball, its whole will
have to reverse velocity in order to change directions, just like when
you throw a ball against a wall (the liquid example simply
demonstrates that the fly, being organic, will do this in very rapid
stages, first the front, then the middle, then th ...[text shortened]... ct appears stationary,
it certainly isn't. Otherwise motion, itself, is a paradox.
Nemesio
Originally posted by Freddie2004Why would the fly even be stationary when it hits the train though? If you look at a slow motion view of a big crashing into a windshield, (if I remember this correctly) you'll see that the bug explodes as it hits the windshield which means the bug guts/goo would be the only stationary part of the bug, right?
This is a paradox that has been puzzling me for a while now. A fly is flying in the opposite direction to a moving train. The fly hits the train head-on. As the fly strikes the front of the train, it's direction direction of movement changes through 180 degrees., because it hits the windscreen and continues as an amorphous blob of fly-goo on the front ...[text shortened]... the logical inconsistancy with this. Or does it explain something about British Rail 😉
Fred
There's a very short period of time during which the fly is stationary, because the acceleration takes place over a period of time. However, this doesn't mean that the *train* must be stationary at that time. The train is still moving, and the point where the fly is stationary happens *before* the fly and train and moving at the same velocity in the same direction.
Also, there's the issue that zero is a discrete point on an infinite continuum between the fly's two velocity points (one negative, one positive). I'm not sure how you resolve that one.
I'll throw something in here.
Firstly assume this:
We as the observers defines movement. Relative motion
does only complicate things.
Lets agree that velocity is change in position per time unit.
This means that if you look at the scene frosen in a single
instant no movement ever occurs. A velocity of zero can therefore be sustanied either indefinditly or no at all.
So saying that the fly stops is just wrong. It has "stoped" only at a single point in time. That single point does not give us enough data
to say anything about its speed or direction. And no matter how small timeslice you'll always measure a change in position. Thus, speed.
The fly never stops. And the train doesnt either :-)
Originally posted by chasparosThat sentence made me come up with this answer...
Lets agree that velocity is change in position per time unit.
The idea was, that the fly stops the train. In other words, the train's speed has to be 0 km/h (mph) then.
The formula for speed is:
speed = distance/time
But what is the time here? It is obviously 0s because as soon as you take a time span larger than 0s, you will also see a movement of the train.
So we can state t = 0s. But since division by zero is not allowed, the speed is definitely not zero. It's not any other value either, but it's also not zero. Therefore, the fly didnt stop the train. qed imo 😛
Originally posted by NemesioPicked this out of context... sorry about that.
This is the problem, Freddie.
.. just like when you throw a ball against a wall..
Fly vs train is NOT the same as Ball vs Wall.
Agreeing again to disregard relativity, the wall is stationary and does not input any energy to the ball, as the train does to the fly.
The sum of forces affecting the ball, is zero. (disregarding gravity and such) So the ball is indead motionless at some point.
(I think. Possibly deformation on the wall makes this statement null an void)
But my point is that they are not the same.