The princplz of dezign suggetz a structural relaxtion is balance
I think.
When you press a key on the piano<span> it causes a small hammer inside the </span>piano<span> to hit a string or strings. Each key is connected to its own hammer or hammers which hit a specific string or number of strings. When the hammer hits a string, it vibrates and </span>makes<span> a sound that is tuned to a specific note.
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Color, lines, shadows, structure, texture.