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| A 'simple' Physics postulation... |
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| SiliconWizard:
Well, I guess it all comes down to the thought that velocity is mathematically zero when the object reaches its maximum altitude. Then the OP assumes "velocity = 0" means "stop". Of course, as others have pointed out, first thing would be to define what "stopping" means. Even if it's a term we use in everyday's language without giving it much thought, I'll just dare a simple definition that looks good enough: an object stops iif its velocity reaches 0 *and* the velocity function at this point is non-derivable. In the OP's example of parabolic motion, velocity indeed reaches 0 at the apex, but is still derivable. So, the object never "stops". Just my 2 cents. |
| TimFox:
It stops, then reverses, with the velocity variable being continuous in time. |
| Zero999:
It sounds similar to a child on a swing, who stops, before swinging back the other way, or the voltage and current in the resonant tank of an LC oscillator. |
| TimFox:
Exactly. All of these time-dependent variables (as functions of time) have extrema (maxima and minima) where the time derivative goes to zero. (When I learned math, we said that the derivative "vanishes", which usage bothered me as a smart-ass student.) |
| dietert1:
This reminds me of a professor at the university, when i was student of physics. I remember the name, but i won't tell. One day in a lecture he started to explain: Since velocity is a vector, it can never become negative. The vector will just change its direction. Isn't that crazy? The question in this thread was posed such as to focus on the vertical component of velocity. And that becomes zero before getting negative. Voting about physics questions, that's modern times! Regards, Dieter |
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