Is a modern piano different than Mozart had?

The modern piano is a more sophisticated instrument. Whether it is better is subjective, but I suppose most people would say it is better. The fortepiano (which generally refers to predecessors of the modern piano from about 1700 to 1840) of Mozart's time was different in a few fundamental ways:

It had much lighter action. This allowed faster, more agile and gentler playing with easier execution of passages requiring great dexterity.

A previous answer has mentioned the smaller keys. On top of this, it was fairly common for the white notes to be coloured black and the black notes to be white, but obviously that did not affect the sound.

Fortepianos would have wooden frames until the iron frame piano was pioneered around Schumann's time (about 20-30 years or so after Mozart). This meant that they were weaker, and strings could not be strung as tightly. As a result the sound was quieter and more mellow; some people complained about the 'harsh' sound of the iron piano in its early days.

Related to the iron frame is the fact that Mozart's piano had a smaller range of about 5 octaves rather than the modern 7 and a half. Bass strings exert more pressure on the frame.

The strings were smaller and more fragile. (Again, the frame).

The hammer head was normally leather rather than felt.

The pedal mechanism was simpler and probably less effective. It was sometimes controlled by levers or the knee rather than with the foot.

Thus the decay is faster and there is less dynamic contrast on the fortepiano. There was a less uniform sound across the range, and in general the sound was softer. We must miss a lot of deliberate use of these characteristics by Mozart and the like by playing their music on the modern piano.

In my opinion: the modern piano is a more versatile, sophisticated and better sounding instrument, but we miss out on a lot of the composers' original intentions when playing their music on a different instrument. Responsible pianists should try to note where composers were deliberately writing idiomatically for the fortepiano, for example using its shorter sustain or different timbres across its register and this will enrich their interpretations of the repertoire on modern day instruments. I wonder also if tempos or some ornamentations may have slowed down in some pieces to accomodate the more cumbersome action of the modern piano.

One example in particular of something very difficult on a modern piano is a chamber music piece by Haydn (can't remember the name, sorry) in which the pianist is expected to do a two note (an octave apart) glissando in one hand moving up and then down with great agility. This is horrifically difficult and loud (and painful!) on the heavier action of a modern piano.

In chamber music, using a modern piano where orignally a fortepiano was written for can also lead to some other performance practice issues such as balance. I'm sure books exist on the subject.

EDIT:

So in summary: I'm sure composers of Mozart's age would have loved to have an instrument like the modern piano to write for, but they didn't. Thus their music is not written for a modern piano but fortepiano.

A modern piano is much bigger. The notes are wider on the piano. I don't know if you are a piano player, but if you are, you have probably ran into some chords that require you to reach a 9th. Back when Mozart played a 9th was a much smaller distance and almost anyone could reach it without difficulty. This being said, the modern day piano has actually made classical pieces much harder to play because the distance between notes are farther apart. As for how the player interpretation of the works changed, I'm not sure for certain, but because of the better pianos today better sound can be produced and more emotion can be put into the songs, I hope that is a good enough answer.

As to being better developed, yes much. Think about a the computer when it first came out and a computer now. Now slow down that processes and stretch it over hundreds of years and there you have the development of the piano.

It's not about changing the sound in Mozart's head. And if if it were it's not an issue we need to or should worry about. Think about it; how do we know what was in Mozart's head? by the letters he wrote, the scores he left us, and the context of the time he lived in. That's really not much to go on. Whenever we try to read "what was in Mozart's head" more likely we are putting our thoughts in His head, not deciphering Mozart's thoughts. This whole notion that we should play music on period instruments assumes that a vital part of the intent of the composer is based on the the exact tone color at their disposal when they composed the piece, that if they knew about modern instruments they would have chosen not to use them. Even though Mozart and most composers of the time wrote for specific instruments and knew their capabilities, they typically took advantage of the maximum capabilities of their instruments and performers, especially as the limits of performers and instruments expanded. When Mozart found a flutist who could play a high C we start to see them, Why would it be any different with tone colour and other techniques? It's also important to realize that musical score is very much like the script to a play. A score tells a performer what you're supposed to play, but at least half of what is actually performed cannot be notated. That's where interpretation comes in. A performer must fill in the gaps of a score that are un-notatable. And if that means using a harpsichord, or modern piano, that is the performers discretion.

Everything is better - but the instruments are essentially the same. The big difference has been metals like in piano strings. These were pretty awful years ago, and that probably made a difference in the sound. But the harp and action were about the same as now.

A piano-forte is defined by the "jack" in the action which throws the hammer into the strings. I would imagine our modern actions might work a little faster and smoother. The action of the "jack" is really pretty complex, and I'm sure it's evolved a little since Mozart's time.

You might be forgiven for taking Mozart a little slower... maybe that's how he had to play it himself on that old piano.

The pianos that are used today have more keys than the ones that were used during Mozarts time. Also, we have added hammers that can change the sound of a note when played. Overall, the modern day piano and the piano during the time of Mozart are the same. We just added extra features.

Yes, the piano that existed in Mozart's day - what would now be referred to as a "fortepiano" - is smaller, simpler, and quieter than a modern grand piano.

Listen for yourself.

http://www.youtube.com/watch?v=6UQM1YGDe5w

http://www.youtube.com/watch?v=zf0XXsx3A_E

http://www.youtube.com/watch?v=RWKbOGMqDVw

I know they are nowhere near the same thing, but put it this way... is a modern-day violin built by Emmanuel Gradoux-Matt (rebuilt, repaired or refurbished) better than one built by Antonio Stradivari?

What Is A Fortepiano