Spring frogs

My thanks to Rob Gardner for the technical details of the components. I'm keeping a print of his offering for use next time I find such a frog.
I feel that the reason for spring frogs wasn't adequately covered, so I'll offer my understanding. The sound you hear as a steel wheel passes over a rigid (conventional) frog is the wheel tread transfering from one running surface onto the other running surface - whether the movement is facing or trailing. Rather sharp sounds.
On a spring frog, there is much less vertical/ pounding movement then on a rigid frog. Thus less sound and less wear.
Last evening I watched a train of bare tables run over a rigid frog. I was about 30 feet above rail level. Because of the skeletal nature of the cars, I could see the frog that each wheel was about to hit. Welders spend their working years hardfacing these rigid frogs.
Future discussions may cover spring points.
On a distantly related note, there is a streetcar frog. Streetcar wheels are too narrow to tolerate a railroad frog, so the car wheels run or their flanges when crossing frogs; up, over and back down again in about three feet. Boston, Toronto, Memphis, New Orleans, San Francisco, Seattle, most trolley museums.