# Strange Relationships of the Circle

dom_quixote
PHOTOGRAPHIC REDUCTION OR ENLARGEMENT The proportions of a circle never change. But... Question:
If a circle is always a circle, then how is it possible that the S/L and {[S/L]/R} ratios of a circle can vary as a function of the radius size?

• weirdoguy and PeroK

Staff Emeritus
Gold Member
Because they aren't unitless quantities. S has units of length squared and L has units of length, so when you double the length, they don't change the same way.

• • mfb and dom_quixote
Gold Member
There are errors in your table for the perimeter. It should read 2/5π and 3/5π 2/3π for the first two. And S/L for R=1/2 is 1/4, not 1.

Last edited:
• dom_quixote and berkeman
Homework Helper
2022 Award
There are errors in your table for the perimeter. It should read 2/5π and 3/5π for the first two. And S/L for R=1/2 is 1/4, not 1.
##\frac 2 3 \pi## ?

• dom_quixote and jack action
If a circle is always a circle, then how is it possible that the S/L and {[S/L]/R} ratios of a circle can vary as a function of the radius size?
Try it with a square if you have problems understanding it for a circle. It's more a geometry question rather than physics.

Related topic:
https://en.wikipedia.org/wiki/Square–cube_law

• dom_quixote and Nugatory
The Fez
There are many basic arithmetic errors in your charts. The [S/L]/R column should always be 1/2, for instance.

• dom_quixote, Nugatory and gmax137
dom_quixote
In fact, I made a mistake .
The corrected table is below: Note in the TABLE I a singularity, when R=2/1:
S = L ?
Certainly not!
S expresses area;
L expresses length.

P.S.:
If there is another error in the table, I apologize for my numerical dyslexia !

Last edited:
• PeroK
Gold Member
How about applying some simple algebra before you make the tables?
Since ##S=\pi R^2## and ##L=2 \pi R## then ##\frac{S}{L} = \frac{\pi R^2}{2 \pi R} = \frac{R}{2}## and ##\frac{(\frac{S}{L})}{R} = \frac{1}{2}##.
That is all there is to this, now you can correct your tables.

• • hutchphd, Nugatory, dom_quixote and 1 other person
S = L ?
Certainly not!
S expresses area;
L expresses length.
They can have have the same numerical value (which is what your table shows), but different units (which your table doesn't show).

If there is another error in the table, I apologize for my numerical dyslexia !
See post #6 and #8.

• dom_quixote
Mentor
Note in the TABLE I a singularity, when R=2/1:
S = L ?
Certainly not!
S expresses area;
L expresses length.
Why don't you use letters that more closely align with what they represent?
R is fine for radius, but why are you using S for area and L for length? Better would be A for area and P or C for either perimeter or circumference.
How about applying some simple algebra before you make the tables?
Or even some simple arithmetic.
You have errors in the first two rows of table 1.
##2\pi \frac 1 5 \ne \frac{5\pi} 2##
##2\pi \frac 1 3 \ne \frac{3\pi} 2##

Last edited:
• dom_quixote
Mentor
• 