This Topic in Depth focuses on the physics of sound waves and its applications in other science realms. The first four educational Web sites concentrate on sound wave properties and musical instruments. Dan Russell, a professor of Applied Physics at Ketting University, created the first site (1) to provide students animated images of sounds and vibrations produced by instruments such as loudspeakers and guitars. This site will surely be of assistance to those struggling with the intangible realities of wave phenomena. Developed by the Wright Center for Science Education, The Physics of Music and Musical Instruments (2) is an online manual designed for high school students and teachers. The instructive Web site discusses the basics of Waves and Sounds and how various instruments work. The next site (3), by Michigan Tech University, talks about various instruments' physical properties. Students can view amplitude, frequency, and time graphs of the clarinet. Users can also learn how to construct their own Native American-like PVC Flute and Wind Chimes. Catherine Schmidt-Jones, in cooperation with the Connexions Project at Rice University, addresses the connection between musical instruments and the physics of sound in the fourth site (4). Designed for an audience from middle school students to adults, users will find educational diagrams and explanations about physics terms such as pitch, frequency, and standing waves. At the end of the site, visitors will find a short quiz to test their knowledge. The next two sites deal with the relationship between biology and the physics of sound. The National Center for Voice and Speech developed mini-courses and tutorials (5) to assist people with difficult concepts in voice production. Intended for those who have taken a college level physics course, users can learn about many topics including frequencies, vocal fold oscillations, and pitch control. The next site (6) is a straightforward document created by Queens University discussing sound, resonance, and hearing. With the incorporation of diagrams and text, visitors can easily learn the basics of how the ear allows people to hear sound waves. The last two Web sites introduce water acoustics. The Acoustic Monitoring Project at NOAA (7) is observing the ocean through underwater acoustics. At this site, visitors can learn about NOAA's studies in Bioacoustics, Ocean Seismicity, and Environmental Noise. The site also offers many animations dealing with Axial eruption, Atlantic Seismicity, and much more. The last site (8), created by Peter Scheifele at the Classroom of the Sea, addresses the basics of waves propagating through water. Students will find numerous acoustic definitions, thought provoking quizzes, and hands-on activities; helping them understand the relatively complicated concepts.