You won't believe this...

90mph is only 145kmh... lolz

 

Yup, the relative speed between 2 objects moving in the same direction is their difference, and the relative speed between 2 objects moving in opposite directions is their sum. I learned that in high school physics. It's counterintuitive at first, but it makes sense if you think about it a little. (of course, this only applies at sub-light speeds)

So, yeah, like you said - as long as the relative speed (velocity is more accurate) is positive and nonzero, the faster object will eventually overtake the slower one.

 

That's not entirely accurate - if you are moving at all, even slowly, there is some element of time compression in effect. So the actual speed differential will be fractionally different from the calculated one, although the difference is so small that in any ordinary circumstances it's impossible to measure.

One interesting exception to this is the GPS system - the satellites are moving fairly fast (two orbits per sidereal day), and the way the GPS system works means that you can recover the satellite internal clock from the ground with a very high degree of accuracy. The combination of these two means that the relativistic effects are actually detectable, and hence the satellites are built with what seems like a small frequency error when tested on the ground, but once they are flying they are spot on.

 

when this baby hits 90mph... you're gonna see some serious shit.

 

Of course, I know that. I was referring to Newtonian physics, which in this situation ought to be a close enough approximation.

Also, 4,000 posts! Woooo!!!!