The relation between the circumference and the radius of a circle is one of the most important concepts explained during the first years in the academic path of a math student. This relation is not a trivial concept and over centuries has fascinated mathematicians and scientists from ancient Egypt to the modern supercomputers whose power has been tested by calculating digits of pi.
Archimedes created an algorithm for calculating pi in his book "Measurement of the circle" but it was Leonard Euler who in 1737 introduced the use of the Greek letter pi to refer to the number we know as pi. Introducing the relation to Elementary and Secondary students for the first time can be a complex task. As a matter of fact, it took mankind centuries to comprehend the nature of pi but nowadays the programs of study spend only a short time explaining it.
Geogebra is a new technology, that stands out among the others and can be extremely useful in explaining the relation between the circumference and the radius of a circle.
The construction of the animation explained in this article provides a valuable didactic resource to facilitate the students' comprehension of the relation.