Simplify the following text for a Grade 5 native English-speaking person.
Original: Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases , liquids , and solids including vibration , sound , ultrasound and infrasound . A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical or audio engineer .
Simplified: Acoustics is the study of sound .