Eighty-eight little catapults
What Happens Inside a Piano?
Pressing a piano key does not push a hammer onto a string. It throws the hammer, and lets go before it lands.
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Step 1 of 5
The hammer is thrown, not pushed.
If your finger stayed connected to the hammer it would rest on the string and stop it dead. A clever linkage throws the hammer the last part of the way and lets go.
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Step 2 of 5
How hard you press is the volume.
A faster key means a faster hammer and a louder note. That single fact is why the instrument replaced the harpsichord, which was the same loudness however you played it.
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Step 3 of 5
Low strings are long, thick and wound.
Length ran out, so they added weight instead Low notes need slow-vibrating strings. The bottom note vibrates only about 27 times a second, and even a grand piano is not long enough for that. So the lowest strings are wrapped in copper wire, to make them heavier without making them longer.
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Step 4 of 5
A damper stops each note.
A felt pad rests on every string. Pressing a key lifts its damper so the string can ring; letting go drops it back, which is why the sound stops when your finger does.
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Step 5 of 5
The right pedal lifts every damper at once.
With all the dampers off, struck notes keep ringing and every other string shivers along in sympathy. That is why the pedal sounds lush rather than merely longer.
A piano's frame carries the pull of over two hundred strings — around twenty tonnes altogether. It is cast iron for exactly that reason.
The short version
A piano throws a felt hammer at a string and releases it in mid-air, with a damper that lands again when you let the key go.
Try it yourself
Press a piano key down slowly enough and no sound comes at all. The hammer was never thrown hard enough to reach.