This document discusses ultrasound and SONAR. It begins by defining ultrasound as high frequency sound waves that are above the range of human hearing. It then lists several medical and industrial applications of ultrasound, such as using it to detect fetal abnormalities, clean teeth, and break up kidney stones. The document defines SONAR as a technique using sound propagation to navigate, communicate, or detect objects underwater. It is commonly used by militaries to detect submarines and by fishermen to locate schools of fish. The document concludes with several multiple choice questions to test the reader's understanding.