What Really Causes Washboard Road?

Physics
What is a washboard road? And what causes one? No doubt you’ve ridden gravel roads that made feel like you were driving across a washboard. You felt like you were being shaken to pieces. Then you noticed the road's parallel ridges and grooves. Each groove was two or three inches from the next one. You slowed your speed to reduce the vibration and thought, “What causes washboard road surfaces, anyway?” Many previous to you have asked this same question. Washboard roads are miserable to travel. Car control suffers from lack of road contact. Accidents result. One Common Explanation for Washboard Road Some suggest1 it is a vehicle’s suspension system that causes seeming random forces to change into a harmonic, feedback pattern that results in compactions (or valleys) and upward displacements…
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