On the nature of motion....

I'm really not sure where to post this, perhaps physics? Maybe someone can guide me.

I am aware of Zeno et al.

Imagine a small fly, flying along a railway track directly towards an oncoming train with flat vertical forward facing surfaces.
The fly hits the train at right angles to the flat surface...... The motion of the fly reverses direction. BUT without coming to a stop, for if it were to come to a stop then that would imply that the train came to a stop also, albeit for an instant. Clearly this is wrong, the train does not stop although it's velocity will have been reduced by an infinitesimal amount.

This would seem to imply that a point can reverse direction of travel without becoming stationary.

Or is this an issue of being stationary relative to some outside reference frame?

Any useful comments appreciated....

Chris

The engineering explanation ¹ is that "the train" isn't a monolithic prefectly rigid object (nor, for that matter, is the fly).
A portion of the train will stop - that bit directly in contact (although when I first heard this conundrum ~40 years ago it was "ball bearing" rather than fly) and deform until the elasticity of the impact sends the fly/ bearing on its way. The material directly subject to the impact will absorb that impact, leaving a dent (even if of negligible/ undetectable depth).

1 There's a mathematical one too, something about instantaneous halt, which, apparently, doesn't count as an actual halt... ;)

Quote:

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Originally Posted by PhDemon

what's the last thing to go through a flys mind as it hits a windscreen? Its anus...

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Go boil your head.