Digital Signal Processing Reference
In-Depth Information
Figure 3.5. The dot moves ½ of
a revolution with each strobe
ash. It appears to alternate on
each side of the circle with each
ash. Can you be sure which
direction the wheel is rotating?
Wheel rotating counterclockwise four times per second, or 4 Hz
Wheel rotating counterclockwise six times per second, or 6 Hz
Figure 3.6. The dot moves counterclockwise
3
/
4
of a revolution with each strobe
ash. But it appears to be moving
backwards (clockwise).
Figure 3.7. The dot moves almost
a complete revolution counter-
clockwise,
7
/
8
revolution with each
strobe
ash. Now it de
nitely
appears to be moving backwards
(clockwise).
Wheel rotating counterclockwise seven times per second, or 7 Hz
Wheel rotating counterclockwise eight times per second, or 8 Hz
Figure 3.8. It looks like the dot has stopped moving! What is happening is that the dot completes exactly one revolution
every strobe interval. You can
'
t tell whether the wheel is moving at all, spinning forwards or backwards. In fact, could
the wheel be rotating twice per strobe interval?
we see is only the “a little bit extra” on every flash. For that matter,
it could go around 10 times plus the same “a little bit extra” and
we couldn't tell the difference.
