What is sound?

1. What is sound?

2. If a tree falls in the woods and no one is around, does it make a sound?

3. When something makes a sound, it vibrates and emits compression or pressure waves that are received in the ear. Our brain then interprets these as sounds.

4. Different types of sounds, such as a scream or music, are characterized by different waveforms. In the case of the human voice, sound waves emitted from the vocal chords are changed by movements of the mouth. Vibrations happen between the molecules in the air. If there is no atmosphere, such as in space, sound does not exist as there are no air molecules to create pressure waves. • In space, no one can hear you scream - Alien

5. But what about the deaf? It is known that deaf people are sensitive to vibrations, or they can feel the music. There are famous examples of deaf musicians, such as the percussionist Evelyn Glennie, or the composer Beethoven. Deaf people feel some of these vibrations and can learn to distinguish between waves of different frequencies and amplitudes.

6. What does sound look like? When you drop a stone into water, waves begin at the point where the stone enters the water and move outwards in all direction. A simple sound wave looks like the ripples in water. They start from a single point and radiate outwards in all directions, three dimensionally.

7. While sound sounds are heard equally in all directions from the point of origin, such as a thunderclap, in reality, most sounds are directional. This means that sounds waves are emitted in a particular direction. Similarly, most devices to capture sound, such as micro phones, are designed to catch sound from a general direction. These are called directional microphones (more about these later in the course). If you think back to Edison’s phonograph, the horn captured as much sound as possible from the wide, open end and funneled it towards the narrow end where it was picked up. This is exactly how our ear functions!