All rhythms have patterns, but not all patterns have rhythm. If you remember that rhythm is the repetition intended for movement while pattern is flat and decorative, you will be able to tell the difference between the two. In art balance makes you feel like all the parts are arranged correctly. A central axis is a dividing line that works similar to a measuring scale for the elements to see if they are equalized on both sides or from top to bottom of an art work. They differ in how elements are arranged around the axis.
Formal balance occurs when equal or very similar elements are placed on opposite sides of the axis.
You can see if objects exactly match on each side for bilateral symmetry, or approximate symmetry if there are some small differences. Radial balance may have four or more matching units and seem to radiate or come out from the middle. This occurs in nature in flowers or the segments of an orange. The principle of design concerned with the size relationship of one part to another is proportion. Objects by themselves are difficult to size unless compared to something else.