Question

What occurs when the pitch increases and the sound source is in motion? explain your answer.

Answer 1

If you're listening to a sound that has a steady pitch, and suddenly the
pitch goes up, then you know that two things could have happened:

EITHER ...

-- The person or other source making the sound could have
raised the pitch of the sound being produced.

OR ...

-- The person or other source making the sound could have
started moving toward you.

OR ...

-- both.

Even if the pitch of the sound leaving the source doesn't change,
you would still hear it increase if the source starts moving toward
you.  That's the so-called "Doppler effect".