A floppy disk looks like this:
Here is the back:
Here you can see where the floppy drive grips the floppy disk surface (which is inside this case -- we'll open it up in a minute). It needs a tight grip to spin the recording surface with as little wobble as possible, so that the data can be written in more precise positions. Still, it's not nearly as precise a motion as with a hard disk, and this is one of the several reasons that floppy disks store less data than hard disks -- you need to be able to read the data back from the same position you wrote it at, so if the disk can wobble more, you need to write a larger blotch so that it's there when you look for it.