On Velocity Addition (2)
Let's work on a simple math problem.
Two children are walking toward each other, when will they meet?
Assume they will meet after time t.
During this time, the first child will have walked a distance of d1=v1*t,
and the second child will have walked a distance of d2=v2*t.
Since d1+d2=d, so we have v1*t + v2*t =d, thus (v1+v2) * t= d,
and finally we get t=d/(v1+v2).
In this example, we used the following definitions and assumptions (maybe unknowingly):
Distance, Time, and Speed (Speed=Distance/Time)
- Evenly distributed space (so we can have d=d1+d2)
- Evenly flowing time (so in the example, we don’t care it is today or tomorrow, at noon or in the evening)
- Any distance or time interval has the same measurement in all reference frames. (so the two children’s time are the same, and their distances walked can be added up).