ZEITREISEN - IAAC

- How fast does the consistency of matter change, e.g. “how many grams of ice melt in a second”?
- How fast supplies in a store get exhausted? Do salaries rise fast or slowly? How fast is rising
unemployment? Etc.
How could you find these values? In all cases you must consider the concrete system, the concrete
conditions and to get the result you need to make some indirect measurements.
Mean speed and immediate speed
If the respective time interval during the change of the system is relatively large with respect to the
process duration we get a MEAN VALUE of the speed. If the process is linear then the mean value is
a good information about the system development. The value does not depend on the magnitude of
the time interval.
A
2
2´
1´
1
1 1´ 2´ 2 time
But if the process diagram looks like this one:
A
5
4
3
2/6
1 2 3 4 5 6 time
we get cordially different values of speed from the different time intervals... The way how we can get a
meaningful information about the system development in this not linear case is to decrease the length
of the time interval. If the time interval is very-very small (infinitely small – going to zero: ∆t → 0 ) we
get an IMMEDIATE VALUE of the speed.
Because in most real cases we don´t know in advance the character of the process it is useful to make
some tests measurements with different length of time intervals or directly measure the immediate
value of speed.
By SPEED we can measure the change of a system but only in the case if we are able to DEFINE
AND MEASURE the system´s characteristics! If we can choose MEANINGFUL CHARACTERISTICS
that give us “good information” about the system. (For example, consider sand. Is it meaningful to
consider about the position and motion of each particular grain separately?)
Unit of time
This quantity is necessary to get values of speed of processes that we can compare each other.
Which unit we use is depending on the length of duration of a process, e.g. our choice of clock must
be always related to the characteristics of a real system. For example, consider only if the following
questions are meaningful:
ZEITREISEN - 16. INTERNATIONALE PROJEKTWOCHE DES IAAC IN TANZENBERG SEITE 43