The differences between grand and upright pianos

I'm reading the book "The Way of Bach" about one of my favorite composers, JS Bach, and the author's 3-year study of his works in his desire to play Bach on the piano. At the outset the author goes to buy a piano and complains that an upright just isn't good enough because the keyboard action requires springs. I wondered what he was talking about as I had never heard this and sure enough, because the hammers are perpendicular to the strings, instead of in line with them like in a grand piano where gravity assists in the action of the hammers, springs are required and are part of a mechanism called a "bridle strap".

Here Stu Harrison of Merriam Music explains the differences in keyboard action between a grand piano and an upright:

Not only is there a difference in how the keyboard action operates but there is a large difference in what the pedals do on a grand piano vs. an upright.

On a grand piano the right-hand pedal is the sustain (or damper) pedal. It moves the dampers that normally will engage with the piano strings when a key is released allowing them to keep ringing and therefore sustain.

Like on a grand, the right-hand pedal on an upright piano is also the sustain pedal and it acts in exactly the same way.

The middle pedal on a grand piano is the sostenuto pedal. This pedal is not commonly used but does allow for different types of effects and sound. It essentially acts as a "selective sustain" pedal. Any keys that are pressed when the pedal is depressed will sustain while all others will not.

The middle pedal on a modern upright, sometimes called a practice pedal, moves a piece of felt between the hammers and the strings, resulting in a much lower volume. Needless to say it also changes the tone of the piano^[1]. This pedal can also be shifted over and locked into place. Some more expensive uprights can replace this with an upright version of the grand piano's sostenuto pedal.

The left pedal on a grand piano is the una corda pedal. This pedal, when depressed, will shift the entire piano action over a bit (you can see the keys physically move when it's depressed) and this results in the hammers hitting only one string for each key instead of the 2 or 3 (depending on what range of the keyboard you're playing) that normally are hit. This not only results in a softer sound, but changes the tone of the piano.

Lastly, the left (soft) pedal on an upright moves the hammers closer to the strings resulting in lower volume. Unlike the una corda pedal on a grand, or the practice pedal on the upright, the tone doesn't really change, it just lowers the volume. It can also make it easier to play soft passages because of the changes in how the key is pressed down as a result of the hammers moving.

Here Stu explains the differences:

https://www.youtube.com/watch?v=TdBl-G1-2ek

It's funny that as someone who is very interested in the piano I had no idea about the pedal differences between the two types of piano. I've always known about how the pedals on a grand work but had no idea that two of the three acted completely differently on an upright. You learn something new every day!