Originally Posted by
Kapusta
I am skeptical of the highlighted claim.
Something returning to its original shape has it not an indication of it being damped (internal or otherwise). In fact, if you deflect a steel beam and let it go with no external damping, (not a common situation, as what it is bolted to may be damped) it will keep moving back and forth (vibrating) because steel itself has low hysteric damping (some, but little). And eventually return to its original shape.
The fact that steel has such low hysteric loss is the reason it makes a good spring for uses like a trampoline and pogo stick. Why would it suddenly have higher hysteric losses when you change the shape to a bike frame?
All a steel spring is is a long piece of steel that gets deflected when you compress the spring. The coil shape just makes it practical to work with. How is a steel bike frame fundamentally different?
First of all, a bicycle frame is not a spring, it is a complex system made up of many different pieces, each with its own properties. More importantly, none of the models that you learn in your undergrad physics or engineering classes are true, they are all approximations. There is no such thing as an ideal spring, springs have mass, they do not have linear restoring forces. If you enclose a real spring in a vacuum and launch it into space it won’t continue to vibrate forever. It may oscillate for a long time but not forever. A real beam which is deflected will not continue to oscillate, it’s not an ideal beam. In fact, a beam is much further from ideal than a simple spring. The more complicated a system becomes the less it behaves as ideal. Every piece of a bicycle frame interacts with every other piece. None of the pieces are ideal, they have properties which contribute to the behavior. That’s not to say that ideal models aren’t useful as a first approximation in a simple scenario but they are inadequate for describing real physical phenomena as you depart further from the ideal.