What is the minimal frequency that can be listened to by a human?

The speed of the sound in normal atmospheric conditions?

The sound travels faster through

Sections of a sound wave:

According to Doppler's effect, when the sound approaches to the listener the pitch is:

What is a repeating disturbance that transfers or moves energy from place to place?  

When 2 waves meet and the amplitude increases it is known as what?

Which wave behavior do noise cancelling headphones use?

When a wave bends around a barrier or passes through an opening, it is called