Explore and understand the principles of longitudinal waves through interactive simulations and No sounds can be heard in outer space because sound waves require a medium, such as air, to travel through. a wave that appears to stand in one place, even though it is really two waves interfering as they pass Gizmo Warm-up Ocean swells are an example of waves. A point of maximum amplitude on a standing wave. Customizable versions of all lesson materials Exploration Sheet Answer Key. Subscribers Onl