Sound

1. produce by

1.1. vibrations of particles in medium

1.1.1. unable to hear in vacum

2. longitudinal waves

2.1. through

2.1.1. compression

2.1.2. rarefaction

2.2. requires a medium

2.2.1. speed of sound

2.2.1.1. solid>liquid>gas

3. has..

3.1. loudness

3.1.1. depends on the amplitude

3.2. pitch

3.2.1. depends on the frequeny

4. consists of

4.1. Ultrasound

4.1.1. INS to insert (Windows)

4.1.2. TAB to insert (Mac OS)

4.1.3. ENTER to add siblings

4.1.4. DEL to delete

4.1.5. All key shortcuts

4.2. audible frequencies of 20Hz to 20khz

4.2.1. echoes can also be heard