# Answer to this 'velocity' question?
**URL:** https://boards.straightdope.com/t/answer-to-this-velocity-question/550614
**Category:** Factual Questions
**Created:** [August 18, 2010, 1:33pm UTC](https://boards.straightdope.com/t/answer-to-this-velocity-question/550614 "2010-08-18T13:33:05Z")
**Posts on this page:** 2
**Page:** 2
### Author:  [@MikeS](https://boards.straightdope.com/u/MikeS)
#### Post date: [August 18, 2010, 11:12pm UTC](https://boards.straightdope.com/t/answer-to-this-velocity-question/550614/21 "2010-08-18T23:12:32Z")
> [@jackdavinci](#):
>
> Whatever problem you’re trying to solve you’re probably conceiving of incorrectly - either there truly is a force, in which case it acts over a period of time, or there’s just an impact in which case you want to use momentum. I suppose you could derive instantaneous force as some kind of limit, but I can’t imagine it approaching anything other than zero.
Physicists often use the [Dirac delta function](http://en.wikipedia.org/wiki/Dirac_delta_function) to model this kind of “sharp pulse”; in this context, it would be the limit in which an infinite force acts over zero time. Of course, saying it that way makes it pretty ill-defined, but assuming you’ve got your [formal mathematical definition](http://en.wikipedia.org/wiki/Distribution_(mathematics)) squared away you can use it in many context like you would any other function.
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### Author:  [@Nametag](https://boards.straightdope.com/u/Nametag)
#### Post date: [August 19, 2010, 2:35am UTC](https://boards.straightdope.com/t/answer-to-this-velocity-question/550614/22 "2010-08-19T02:35:44Z")
As expressed above, the problem is not solvable. If you apply a constant force over an unknown distance or time, you can’t know the final velocity. And it’s even more impossible if you try to express the motive force as a WHUMP.
There it is.
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