There are at least 5 qualities of a note that make it unique:
- pitch (which note is it on a piano keyboard)
- rhythm (how long is the note)
- tempo (how fast or slow is the note)
- timbre (what is the unique voice/color/quality of the sound of the note)
- volume (how loud or soft is the note).
I love knowing even the smallest reason WHY in music. Here’s a video about note qualities that talks about some of the science behind these note qualities (someday I’ll understand everything he’s talking about!):