The doppler effect is the apparent change in caused by relative motion between the source of the wave and the observer.

The correct answer is frequency

The Doppler effect is characterized by the change in the sound frequency emitted by a source, perceived by an observer when there is relative movement. A typical example of the Doppler effect is the case of an ambulance with the siren on, during the approach or removal of an observer.

answer; cattle ranching on the savanna,and forestry in the amazon;

i believe the answer is:   psychological  experiment

in this experiment, wilhelm wundt became the first person that implement scientific method in analyzing the pyschological phenomenon.

due to this result, wilhelm wundt also able to make psychology to be acknowledged as a separate scientific field from biology.