At one time, fighter pilots thought they could never fly faster than the speed of sound. Now, many planes--and the people in them--hurdle through the sky at Mach 1! Readers will find sound a fascinating subject as they discover the many ways this form of energy is used today, including ultrasound machines that allow doctors to check on unborn babies and the various pitches of musical instruments used in music. Including information about how human and animal ears hear, the main science content will enhance physical science knowledge learned in the classroom. Fact boxes and colorful photographs help readers relate to the concepts of sound travel, echo, and sound pollution, among others. From beginning to end, the basics of sound come through loud and clear!