Sound can exhibit fascinating phenomena that can be observed in our everyday lives. Let's explore three intriguing sound phenomena: echoes, resonance, and the Doppler effect.

Echoes occur when sound waves bounce off surfaces and return to our ears. Imagine standing near a tall mountainside and shouting 'hello.' The sound waves travel to the mountain and bounce back, reaching your ears as a delayed repetition of the original sound. This phenomenon can also be observed in empty rooms with reflective surfaces.

Resonance is the phenomenon in which an object vibrates at its natural frequency when exposed to a sound wave with the same frequency. For example, when a singer hits a high note, a crystal glass might resonate and shatter due to the matching frequency of the sound wave. Another notable example of resonance is the Tacoma Narrows Bridge collapse, where the bridge's natural frequency was excited by strong winds, causing it to vibrate and collapse.

The Doppler effect refers to the perceived change in frequency of a sound wave when the source of the sound or the observer is in motion relative to each other. A common example is the change in pitch of an ambulance siren as it approaches and then passes by. As the ambulance moves towards the observer, the sound waves are compressed, resulting in a higher frequency and a higher pitch. As the ambulance moves away, the sound waves are stretched, resulting in a lower frequency and a lower pitch.

These interesting sound phenomena not only provide us with a deeper understanding of the nature of sound but also have applications in various fields, including music, engineering, and scientific research.