ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Longitudinal wave in a spring. The wave motion is parallel to the direction of travel, with regions alternating between compression (lower centre) and expansion (upper centre) as the wave passes. This is in contrast to transverse waves where the wave motion is perpendicular (at right angles) to the direction of travel. Sound and pressure waves are examples of longitudinal waves.
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