By the end of the previous section, you probably learn to expect to see keys moving when pressing on the left pedal, aka soft pedal or Una Corda pedal, on a grand piano.
So what about the upright model? Are we supposed to see the keys moving as well?
The pedal down-keys shifting to the right only happens with the soft pedal on grand piano. Apart from this condition, you should not see any piano key moving (right or not right). If you do, please call a piano repairer for this piano has some serious issues needs to be fixed.
Then what function does the left pedal in the upright model offer?
The left pedal on the upright model is still a soft pedal, but not a Una Corda pedal, for it does not cause the hammers to strike 2 strings instead of 3 strings.
Before the explanation, there is one new terminology needed to be learned in this article: the hammer rail.
A hammer rail is a rail that has a thick soft piece of cloth glued to it and serves as a rest for the hammers.
When the left pedal is pressed down in an upright piano, the hammer rail is pushed toward the string, causing the hammers to be about halfway to the strings and the distances between the hammers and the strings are now SHORTER. Because the hammers has less distance to accelerate towards the strings, less energy is transmitted unto the strings when the keys are pressed, producing a quieter (softer) tone.
So if you are pressing down a left pedal on an upright model, do not expect the keys to move like those from the grand model.